Lettuce plant having delayed bolting and shade tolerance

Abstract

The present invention relates to a Lactuca sativa plant having delayed bolting and / or shade tolerance, wherein said plant comprises in its genome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene. The present invention provides a seed from which the Lactuca sativa plant according to the present invention can be grown.

Description

[0001]Nunhems Netherlands B.V. 240134WO011LETTUCE PLANT HAVING DELAYED BOLTING AND SHADE TOLERANCEFIELDThe present invention relates to the field of plant breeding. Provided is a Lactuca sativa planthaving delayed bolting and / or shade tolerance, wherein said plant comprises in its genome atleast one copy of a mutant allele of the Phytochrome B (PhyB) gene. The present inventionprovides a seed from which the Lactuca sativa plant can be grown. Further provided are a plantcell, tissue or plant part of the plant or of the seed comprising the mutant allele of the PhyB gene.The present invention also provides a method for identifying and / or selecting a Lactuca sativa plant or plant part comprising determining whether said plant or plant part comprises in its genome at least one copy of a mutant allele of the PhyB gene.Also, a genotyping assay for detecting the mutant allele is provided, which can be used e.g. inmarker assisted selection of the mutant allele. Further provided is a method for generating aLactuca sativa plant comprising a mutant allele which delays bolting and / or confers shade tolerance when the mutant allele is present in homozygous form. Further provided is a method of producing a lettuce crop, comprising growing a plant comprising preferably two copies of the mutant allele which delays bolting of the crop and / or confers shade tolerance to the crop, whereby the delay in bolting increases the harvest window by e.g. at least 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or more days.In another aspect the lettuce plant comprising the mutant PhyB allele in homozygous formcomprises tolerance to shade and FarRed light supplementation (low Red:FarRed ratios),whereby the plant can be grown at a higher plant density and / or in conditions where higheramounts of FarRed light are present without showing symptoms of Shade Avoidance seen in wild type plants (such as increased internode length, increased plant height). As plants can be grown at higher densities, overall yield can be increased while maintaining leaf quality. Especially in indoor farming systems, such as hydroponic culture, the mutant plants can be grown under growing conditions (e.g. light spectrum, temperature regimes, plant densities) under which wildtype plants show shade avoidance symptoms and e.g. yield and / or quality loss.BACKGROUNDBolting is an essential process in the growth and development of a lettuce plant (Lactuca sativaL.). Bolting is the switch from vegetative to reproductive stage, when the stem extends to makeflowers. Environmental stress, such as an increased temperature or high FarRed (FR) lightconditions, can induce bolting of the lettuce plant, which decreases both the quality and quantityof the harvested plant material. Resistance to early bolting accordingly is an important trait in breeding of lettuce cultivars, whereby the harvest window can be broadened.Lettuce cultivars may vary widely in the number of days necessary from sowing to bolting andflowering. Although there is natural variation in late bolting at the disposal of the breeders toachieve the genetic improvement, complexity of inheritance makes it challenging to breedefficiently. This is partially caused by the fact that the molecular mechanisms regulating the boltingand flowering characteristics in lettuce are largely unknown. Also, as reviewed by Han et al.2021(Frontiers in Plant Science, doi: 10.3389 / fpls.2021.632708), 167 QTLs have been described inNunhems Netherlands B.V. 240134WO012 lettuce for bolting, flowering time or both. By merging overlapping QTL intervals, the authors reduced the number of QTLs to 67. Bolting and flowering time QTLs are located on all of the 9chromosomes of the lettuce genome, see Figure 1 of Han et al.Thus, Han et al. (Frontiers in Plant Science, 2021, ‘A Composite Analysis of Flowering TimeRegulation in Lettuce’, Volume 12, Article 632708) provide a very extensive review of all the currently available information on the regulation of bolting and flowering time in lettuce and Arabidopsis. In this review the high complexity of the different pathways that regulate bolting and flowering is shown in e.g. Table 1 and Figure 1, with 405 lettuce genes being involved, most of which have two or more paralogs in lettuce, and 110 Arabidopsis genes had only one lettuce ortholog. The transition between vegetative and reproductive growth in lettuce is influenced by many genes and several pathways, that interact with one another. The main pathways are described in the review as being the vernalization and autonomous pathway, the ambient temperature pathway, the photoperiod pathway, the gibberellic acid pathway, the aging pathway and the sugar pathway. Overall, it is clear that many pathways and many genes are involved in the floral transitions in lettuce and that these are poorly understood. Regarding the photoperiod pathway the authors conclude that the genetic determinants underlying the photoperiod response have not been well characterized in lettuce, which is a facultative long day plant for which floraltransition is promoted by long day conditions and is delayed, but not completely inhibited, undershort day conditions.Han et al. 2021 (Theoretical and Applied Genetics 134: 3473 – 3487) study an F6 population of236 recombinant inbred lines (RILs) that were developed from a cross between a late-flowering,photoperiod sensitive Lactuca serriola accession (Armenian999) and an early flowering,photoperiod sensitive Lactuca sativa accession (landrace PI251246) to map flowering time loci(FT) and photoperiod sensitivity (PPS) loci. Nine QTLs were identified for these two traits. As theQTLs did not co-locate they conclude that FT and PPS are controlled by separate genetic determinants.Hu et al. 2023 (Theoretical and Applied Genetics 136: 68) found that a large (5.5kb)retrotransposon inserted into the cucumber PhyB gene (CsPhyB) results in early flowering incucumber. Therefore, loss-of-function of CsPhyB resulted in early flowering. The csphyB mutantprotein lacks the entire C-terminal part of the protein. PhyB proteins consist of two parts, the N- terminal part, which is the Photoreceptor Module and the C-terminal part, which is involved in dimerization of phytochrome B and downstream regulatory functions. On page 68, LH Column,the authors mention that the phenotype seen in the knockout CsPhyB gene is the same as for allreported phyB mutants in other plants, such as Arabidopsis, tomato, Brassica rapa, rice, sorghum, and wheat, namely early flowering and long hypocotyls, as seen in the loss-of-function csphyB mutant.Pearce et al. 2016 (BMC Plant Biology 16: 141) describe in Figure 4 in a simplified model howthe dicot Arabidopsis and the tetraploid wheat differ in the photoperiodic regulation of flowering.In Arabidopsis the photoperiod response is regulated by CONSTANS (CO) and in the absence ofPhyB CONSTANS protein accumulates and induces flowering. In contrast the model is much more complicated for wheat, where both PhyC and PhyB are involved. PhyC null mutants show delayed flowering but are still able to produce normal flowers and seeds, while phyB null mutantsare sterile and do not produce seeds at all.Nunhems Netherlands B.V. 240134WO013 Park et al. 2021 (Plant Genome, DOI: 10.1002 / tpg2.20086) describe the genetic diversity between the five major horticultural lettuce types: butterhead, crisphead (iceberg), leaf, Romaine (cos) and stem types. Phylogenetic analysis showed that each type formed a distinct cluster, reflecting strong genetic differentiation between the lettuce types. They found that crisphead lettuce had the lowest genetic diversity and was most distantly related to the other types. They also identify QTLs on chromosome 6 and 7 which were associated with late bolting and their findings provide evidence that strong selection pressure for delayed bolting has played a role in limiting the genetic variation in crisphead lettuce types.There is a need to develop improved lettuce cultivars that show a delayed bolting, which extendsthe harvest window and / or tolerance to shade or high FarRed light conditions (e.g. a lowRed:FarRed ratio), which allows growing lettuce under high plant densities or under higher far-red light conditions (i.e. lower Red:FarRed light ratios) without seeing the typical, non-desirablesymptoms of Shade Avoidance. It is, therefore, an object of the invention to provide a Lactucasativa plant, cells, tissues and other parts of such plant comprising in their genome an allele thatis capable of delaying bolting of said plant. It is a further object of the invention to provide aLactuca sativa plant, cells, tissues and other parts of such plant comprising in their genome anallele that is capable of producing a Lactuca sativa plant having tolerance to shade (referred toas ‘shade tolerance’ herein), whereby lettuce plants can be grown at a higher density and / or underhigher far-red light conditions (e.g. a low Red to FarRed light ratios).WO2022 / 234045 discloses lettuce mutants comprising shade tolerance. The mutants comprise either a mutation in the endogenous LsKO gene and / or in the endogenous Ls20ox1-B gene of lettuce. The mutants were selected under green filter (green plastic foil), which resulted in a R:FR ratio of 0.30 compared to normal light (R:FR ratio above 1.0). Mutants were selected for havingreduced shade avoidance symptoms: not having elongated hypocotyl and petiole, dark greenleaves and large leaf lamina. In homozygous form the three selected mutant had short internodescompared to the wild type (p25). In Horticulture 2023 (9, 1100, Eylands and Mattson) experiments were carried out by applying supplement FarRed light to lettuce seedlings at the seedling stage only and then transplanting seedlings into a hydroponic nutrient film technique (NFT) system with normal lighting (white LEDs) to grow the plants to maturity, as supplement FarRed light induces undesired effects such as bolting. The effects of FarRed treatment on the seedlings (FR induced Shade Avoidance symptoms such as increased leaf length, leaf area and plant height) were lost again at the mature stage. SUMMARYIn one aspect a Lactuca sativa plant or plant part or seed is provided comprising in its genome atleast one copy of a mutant allele of the Phytochrome B (PhyB) gene, wherein the wild type PhyBgene encodes a protein of SEQ ID NO: 1, or a protein comprising at least 95%, 96%, 97%, 98%or 99% amino acid sequence identity to (the wild type protein of) SEQ ID NO: 1, and wherein themutant allele encodes a mutant protein comprising one or more amino acids inserted, deleted and / or replaced compared to the wild type protein, whereby the mutant protein has a reduced function or loss-of-function and confers one or more of the following phenotypes when the mutant allele is in homozygous form: a) delayed bolting compared to the plant comprising the wild typePhyB allele in homozygous, b) no (or significantly less) increase in internode length and / or plantNunhems Netherlands B.V. 240134WO014 height under conditions where the plant comprising the wild type PhyB allele in homozygous formshows an increase in internode length and / or plant height, especially wherein these conditionsare shade, seedling densities of at least 200 plants / m2 and / or high Far Red light (e.g. aRed:FarRed ratio of 0.4). Phenotype b) is in one aspect also referred to as ‘shade tolerance’ or‘increased shade tolerance’ herein. Thus, phenotype b) can also be referred to as the plantcomprising “shade tolerance” or the mutant allele conferring “shade tolerance” when the mutant allele is in homozygous form.In a further aspect a Lactuca sativa plant or plant part or seed is provided comprising in its genomeat least one copy of a mutant allele of the Phytochrome B (PhyB) gene, wherein the wild typePhyB gene encodes a protein of SEQ ID NO: 1, or a protein comprising at least 95%, 96%, 97%,98% or 99% amino acid sequence identity to (the wild type protein of) SEQ ID NO: 1, and wherein the mutant allele comprises at least one or more nucleotides inserted, deleted and / or replaced inthe promoter sequence of SEQ ID NO: 7 (or a promoter sequence comprising at least 95%sequence identity to SEQ ID NO: 7), whereby the mutant allele is not expressed or is expressed to a lower extent than the wild type allele and wherein the mutant allele confers one or more of the following phenotypes when the mutant allele is in homozygous form: a) delayed bolting compared to the plant comprising the wild type PhyB allele in homozygous, b) no (or significantlyless) increase in internode length and / or plant height under conditions where the plant comprisingthe wild type PhyB allele in homozygous form shows an increase in internode length and / or plantheight, especially wherein these conditions are shade, seedling densities of at least 200 plants / m2and / or high Far Red light (e.g. a Red:FarRed ratio of 0.4). Thus, phenotype b) can also be referredto as the plant comprising “shade tolerance” or the mutant allele conferring “shade tolerance” when the mutant allele is in homozygous form.Therefore, in one embodiment a Lactuca sativa plant or plant part or seed is provided comprisingin its genome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene, whereinthe mutant allele comprises a mutation in the promoter sequence of SEQ ID NO: 7 (or a promotersequence comprising at least 95% sequence identity to SEQ ID NO: 7) resulting in decreased (orreduced) gene expression or no gene expression compared to a corresponding wild type allele, or wherein the mutant allele encodes a protein comprising a deletion, truncation, insertion and / or replacement of one or more amino acids, compared to the protein encoded by the wild type allele, resulting in a reduced-function or loss-of-function of the LsPhyB protein, wherein the mutant alleleconfers delayed bolting, e.g. delays the start of bolting of the Lactuca sativa plant by at least 7, 8,9, 10, 11, 12, 13 or 14 days (or more, e.g. by at least 15, 16, 17, 18, 19, 20, 21 or more days) when the mutant allele is present in homozygous form compared to the control plant lacking the mutant allele, and / or wherein the mutant allele causes shade tolerance, e.g. prevents (or reduces)elongation of the internodes and / or prevents (or reduces) increased plant height under highdensity stress (such as at least 200 plants per m2) and / or under light stress conditions (such asshade and / or high FarRed light, e.g. low Red:FarRed ratios) when the mutant allele is present inhomozygous form compared to the control plant lacking the mutant allele, wherein the LsPhyB protein of the wild type allele is encoded by nucleic acid molecules selected from the group consisting of: a) nucleic acid molecules, which encode a protein with the amino acid sequence given under SEQ ID NO: 1;Nunhems Netherlands B.V. 240134WO015 b) nucleic acid molecules, which encode a protein, the sequence of which has an identity of at least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQ IDNO: 1;c) nucleic acid molecules, which comprise the nucleotide sequence shown under SEQ ID NO: 5 or a complimentary sequence thereof;d) nucleic acid molecules, which have an identity of at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% with the nucleic acid sequences described under c);e) nucleic acid molecules, which hybridize with at least one strand of the nucleic acid molecules described under a), b), c), or d) under stringent conditions of at least one wash in 0.2X SSC at a temperature of at least 50°C for 20 min; and f) nucleic acid molecules, the nucleotide sequence of which deviates from the sequence of the nucleic acid molecules identified under a) or b) due to the degeneration of the genetic code. In one aspect the mutant allele is not expressed due to a mutation in the promoter sequence andno wild type LsPhyB mRNA and protein is produced by the mutant allele.In one aspect the mutant allele comprises a deletion, truncation, insertion and / or replacement of one or more amino acids, compared to the protein encoded by the wild type allele, resulting in areduced-function or a loss-of-function of the LsPhyB protein. In one aspect the mutant allelecomprises a deletion, truncation, insertion and / or replacement of one or more amino acids in the C-terminal part of the LsPhyB protein, whereby e.g. the dimer formation (dimerization) of theLsPhyB proteins is destabilized or prevented.In one aspect the mutant allele encodes a mutant protein comprising one or more amino acidsinserted, deleted (e.g. the protein is truncated through a premature STOP codon in or precedingany one of the C-terminal domains) and / or replaced in one or more of the conserved C-terminal domains of the protein selected from the Modulator Loop, the PAS1-domain, the PAS2-domain, the HKRD-domain and the HATPase Phy-like domain. In one aspect the mutant allele encodes a mutant protein comprising a truncation whereby the protein is truncated in or preceding one of the conserved C-terminal domains of the protein selected from the Modulator Loop, the PAS1-domain, the PAS2-domain, the HKRD-domain and the HATPase Phy-like domain, i.e. in or preceding the Modulator Loop-domain, whereby the remaining amino acids of the C-terminal are missing, in or preceding the PAS1-domain, wherebythe remaining amino acids of the C-terminal are missing, or in or preceding the PAS2-domain,whereby the remaining amino acids of the C-terminal are missing, or in or preceding the HKRD- domain whereby the remaining amino acids of the C-terminal are missing, or in or preceding theHATPase Phy-like domain whereby the remaining amino acids of the C-terminal are missing.Without prejudice, the Q750STOP mutant generated by the inventors is believed to result in acomplete loss-of-function of the LsPhyB protein, as is confirmed by the shade tolerancephenotype seen in the mutant when the mutant allele was in homozygous form. In cucumber asimilar loss-of-function mutant is described which had a transposable element inserted in- between the Phy-domain and the PAS1 domain, resulting in the CsPhyB amino acids 599 to 1132Nunhems Netherlands B.V. 240134WO016 of SEQ ID NO: 8 being absent in the mutant (Hu et al.2023 Theoretical and Applied Genetics 136:68). That the Q750STOP codon mutant is indeed a loss-of-function mutation was further conformed by additional STOP codon mutants, see Examples. The Q750STOP mutant is in the Modulator Loop domain and precedes the conserved PAS2- domain of the protein and results in the absence of amino acids 750 to 1125 of the wild type protein of SEQ ID NO: 1 and thereby a loss of three conserved C-terminal functional domains ofthe LsPhyB protein: the PAS2-domain, the HKRD-domain and the HATPase Phy-like domain asshown in Figure 3.Other mutants (e.g. reduced-function mutants or null-mutants or loss-of-function mutants) can beeasily generated, e.g. by gene editing techniques, and the phenotype can be compared with theQ750STOP mutant and mutants can be selected which result in e.g. the same or similarphenotype when in homozygous form as seen for the Q750STOP mutant. Other mutants are e.g. described in Example 6, for example Q91STOP, which is at the N-terminal and precedes all of the conserved domains, W369STOP, which is in the GAF domain (resulting in absence of the Phy domain, PAS1 domain and all remaining C-terminal domains, see Figure 3), W524STOP and Q549STOP, which are in the Phy domain, Q612STOP, which precedes the PAS1 domain and E707STOP which is in the PAS1 domain. All these stop codon mutants precede the Q750STOP mutant and precede the Modulator loop domain and result in absenceof the remaining C-terminal region. Without prejudice and without limiting the invention, they arethought to result in the same or very similar phenotype as the Q750STOP mutant, which is in the Modulator loop domain. For three STOP codon mutants it has been confirmed that they result in a delayed bolting phenotype when the mutant allele is in homozygous form. These mutants are a Q91STOP mutant, a W369STOP mutant and a W524STOP mutant. In all three mutants the entire C-terminal region of the protein is missing and in the Q91STOP mutant almost the entire protein is missing, as only the first 90 amino acids of the protein remain. These mutants confirm that mutants which result ina loss-of-function of the encoded LsPhyB protein result in e.g. delayed bolting. Therefore, anyloss-of-function mutant, e.g. any mutant that results in e.g. a premature STOP codon in or preceding the Modulator Loop domain, is encompassed herein.In one aspect the mutant LsPhyB allele is a null-allele, i.e. the allele is not expressed (e.g. due toa mutation in the promoter) or the protein product of the allele is not functional in the plant (e.g. due to a mutation in the allele leading to a non-functional protein). In one aspect the plant or plant cell comprises at least one copy of a null mutant allele for theLsPhyB gene, i.e. said null allele results in no expression of the wild type gene and therefore noproduction of any wild type protein, or said null allele encodes a loss-of-function protein, through e.g. an insertion, replacement and / or deletion of one or more nucleotides in the gene resulting in insertion, replacement and / or deletion of one or more amino acids. A null allele or knock-out allele is an allele resulting in absence of wild LsPhyB protein being made by that allele in the cell or tissues where the wild type LsPhyB protein is normally produced or resulting in a loss-of-function protein being made by that allele in the cell or tissue where the wild type LsPhyB protein is normally produced. Thus, when a null allele is present in a plant or plant cell in homozygous form, no functional LsPhyB protein is made by the cell or plant homozygous for the null allele.Nunhems Netherlands B.V. 240134WO017In one aspect the endogenous wild type LsPhyB allele is deleted completely, or is deletedpartially, or comprises a DNA insert in the allele (e.g. a transposon or a transposon like element being inserted, or a DNA fragment being inserted), whereby the allele is a null allele.As mentioned, the wild type LsPhyB protein comprises 7 highly conserved domains, the GAFdomain, the Phy-domain, the PAS1 domain, the Modulator Loop domain, the PAS2 domain, the HKRD domain and the HATPase-Phy-like domain, see Figure 3.PhyB proteins are dimers in plants and the C-terminal end of the protein is responsible fordimerization. Li et al. 2022 (Nature Vol 604, p127-133) studied the Arabidopsis PhyB structureusing cryo-electron microscopy. The found a complex dimeric organization, with the C-terminal HKRD-domains associated head-to-head and the N-terminal photosensory region associated head-to-tail. They also found that there is a Modulator Loop domain preceding the PAS2 domainand that both the Modulator Loop domain and the PAS2-domain strengthen the inter- andintramolecular contacts.Therefore, in one aspect the absence or modification of all or part of the PAS2 domain and / or ofall or part of the Modulator Loop domain will likely prevent dimerization and render the PhyB non-functional or at least having a reduced function in vivo (e.g. destabilizing or preventing PhyB dimerformation), leading to the delayed bolting phenotype and / or the shade tolerance phenotype asseen e.g. for the Q750STOP mutant. In one aspect the mutant allele encodes a non-functional (or reduced function, e.g. havingdestabilized or no dimer formation) protein which comprises one or more amino acids inserted,deleted and / or replaced in the Modulator Loop domain and / or in the PAS2-domain of the wild typeprotein or preceding the Modulator Loop domain or preceding the PAS2-domain of the protein. Inone aspect the mutant allele encodes a truncated protein lacking all or at least part of the Modulator loop domain and the remaining C-terminal amino acids. The wild type Modulator Loop domain is the domain starting at (and including) amino acid 745 and ending at (and including) amino acid 765 of SEQ ID NO: 1 or the equivalent amino acids of a wild type protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1. The wild type PAS2 domain is the domain starting at (and including) amino acid 752 and ending at (and including) amino acid 874 of SEQ ID NO: 1 or the equivalent amino acids of a wild type protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1. In one aspect the mutant allele encodes a protein which lacks at least one or more (or all) aminoacid of the Modulator Loop domain and / or of the PAS2 domain of SEQ ID NO: 1 (which ModulatorLoop domain starts at amino acid 745 and ends at amino acid 765 of SEQ ID NO: 1, or theequivalent amino acid of a sequence comprising at least 95%, 96%, 97%, 98% or 99% with theamino acid sequence given under SEQ ID NO: 1 and which PAS2 domain starts at amino acid752 and ends at amino acid 874 of SEQ ID NO: 1, or the equivalent amino acid of a sequencecomprising at least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQ ID NO: 1) or wherein one or more amino acids of the Modulator Loop domain and / or of the PAS2- domain are replaced by one or more different amino acid or are missing, e.g. due to a stop codon mutation in a codon preceding the codons of the Modulator Loop domain and / or preceding the PAS2-domain or in a codon of the Modulator Loop domain and / or in a codon of the PAS2-domainNunhems Netherlands B.V. 240134WO018or due to an insertion, deletion and / or replacement of one or more nucleotides into the transcribedregion or coding region of the gene, leading to a reduced function or preferably loss-of-function LsPhyB protein. For example, the mutant allele may encode a truncated protein wherein at least one or more amino acids of the C-terminal end, including e.g. one or more amino acids of the Modulator Loopdomain and / or of the PAS2-domain are missing, e.g. the encoded protein may e.g. only compriseamino acids 1 to V749, due to e.g. DNA insertion between the codon for V749 and Q750 or dueto a STOP mutation. In one aspect any codon for amino acid 1 to 744, or 1 to 765, or 1 to 751, or 1 to 750, or 1 to 874,or 1 to 895, or 1 to 960, or 1 to 1006, or 1 to 1007, or 1 to 1020 of SEQ ID NO: 1 (or the equivalentamino acid in a sequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1) may be changed into a premature STOP codon, whereby the truncated protein isrendered non-functional (or having reduced function, e.g. destabilizing or preventingdimerization), or wherein the mutant allele at least results in delayed bolting and / or shade tolerance when the mutant allele is in homozygous form. In one aspect the codon for Q91, or for W369 or for W524 or for Q750 is changed into a premature STOP codon. In one aspect the mutant allele encodes a truncated protein as described in Example 6.Thus, in one aspect the mutant LsPhyB protein comprises one or more amino acids replaced,deleted and / or inserted in the conserved Modulator Loop domain and / or in the PAS2-domain ofthe protein or preceding the Modulator loop domain or the PAS2-domain of the protein. Thisinsertion, deletion and / or replacement of one or more amino acids of the Modulator Loop domain or the PAS2-domain or preceding the Modulator loop domain or the PAS2-domain preferablyrenders the protein non-functional in vivo, or having reduced function in vivo (e.g. destabilizing orpreventing dimerization), or at least results in delayed bolting and / or shade tolerance when themutant allele is in homozygous form, as can be tested by the phenotype when the mutant alleleis in homozygous form. Thus, although it is believed that the Q750STOP mutant renders the PhyB protein completely non-functional in vivo, it is also encompassed herein that the mutant protein has a reduced function in vivo, e.g. the mutation has still some residual functionality but that the mutation e.g. atleast destabilizes or prevents dimer formation of the protein. Such a reduced function protein,whereby e.g. no stable LsPhyB protein dimers are formed, may lead to the delayed bolting and / orshade tolerance phenotype. In one aspect, therefore not only ‘non-functional’ or ‘loss-of-function’mutant proteins are encompassed herein but also a reduced-function mutant proteins (and mutantalleles encoding such reduced function mutant proteins) whereby e.g. no dimers or no stabledimers of the LsPhyB protein are formed in vivo. Such reduced function mutant proteins aretherefore encompassed herein with the proviso that the mutant allele in homozygous form resultsin a delayed bolting phenotype and / or shade tolerance phenotype, as e.g. described for the Q750STOP mutant. In one aspect, at least one amino acid of the conserved Modulator domain and / or in the PAS2-domain or preceding the conserved Modulator domain or the PAS2-domain is deleted, insertedand / or replaced by another amino acid or by a STOP codon or one or more amino acids of theModulator domain or of the PAS2-domain or preceding the Modulator Domain or PAS2-domainNunhems Netherlands B.V. 240134WO019 are not transcribed and translated due to an insertion, deletion and / or replacement of one or morenucleotides into the allele, resulting in e.g. a loss-of-function (or reduced function) of the proteinand / or resulting in at least delayed bolting and / or shade tolerance when the allele is inhomozygous form (when no wild type allele is present in the diploid plant or plant cell).As mentioned, the C-terminal end of the protein comprises five conserved domains, the ModulatorLoop domain, PAS1-domain, the PAS2-domain, the HKRD-domain and the HATPase Phy-like domain.In one aspect, at least one amino acid of the conserved Modulator Loop-domain or preceding theconserved Modulator Loop-domain is deleted, inserted and / or replaced by another amino acid orby a STOP codon or one or more amino acids of the Modulator Loop-domain or preceding theModulator Loop domain are not transcribed and translated due to an insertion, deletion and / or replacement of one or more nucleotides into the allele, resulting in e.g. a loss-of-function (orreduced function) of the protein and resulting in at least delayed bolting and / or shade tolerancewhen the allele is in homozygous form (when no wild type allele is present in the diploid plant or plant cell). The wild type Modulator Loop domain is the domain starting at (and including) amino acid 745 and ending at (and including) amino acid 765 of SEQ ID NO: 1 or the equivalent amino acids of a wild type protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1. In one aspect the mutant allele encodes a protein which lacks at least one or more (or all) aminoacid of the Modulator Loop domain of SEQ ID NO: 1 (which Modulator Loop domain starts atamino acid 745 and ends at amino acid 765 of SEQ ID NO: 1, or the equivalent amino acid of asequence comprising at least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQ ID NO: 1) or wherein one or more amino acids of the Modulator Loop-domain are replaced by one or more different amino acid or are missing, e.g. due to a stop codon mutation in a codon preceding the codons of the Modulator Loop-domain or in a codon of the Modulator Loop-domain or due to an insertion, deletion and / or replacement of one or more nucleotides into thetranscribed region or coding region of the gene, leading to e.g. a reduced function or preferablyloss of function LsPhyB protein and resulting in at least delayed bolting and / or shade tolerancewhen the allele is in homozygous form (when no wild type allele is present in the diploid plant or plant cell).In one aspect, at least one amino acid of the conserved PAS1-domain or preceding the conservedPAS1-domain is deleted, inserted and / or replaced by another amino acid or by a STOP codon orone or more amino acids of the PAS1-domain or preceding the PAS1 domain are not transcribedand translated due to an insertion, deletion and / or replacement of one or more nucleotides into the allele, resulting in e.g. a loss-of-function (or reduced function) of the protein and at least delayed bolting and / or shade tolerance when the allele is in homozygous form (when no wild type allele is present in the diploid plant or plant cell). The wild type PAS1 domain is the domain starting at (and including) amino acid 622 and ending at (and including) amino acid 739 of SEQ ID NO: 1 or the equivalent amino acids of a wild type protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1.Nunhems Netherlands B.V. 240134WO0110 In one aspect the mutant allele encodes a protein which lacks at least one or more (or all) aminoacid of the PAS1 domain of SEQ ID NO: 1 (which PAS1 domain starts at amino acid 622 andends at amino acid 739 of SEQ ID NO: 1, or the equivalent amino acid of a sequence comprisingat least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQ ID NO: 1) or wherein one or more amino acids of the PAS1-domain are replaced by one or more different amino acid or are missing, e.g. due to a stop codon mutation in a codon preceding the codons ofthe PAS1-domain or in a codon of the PAS1-domain or due to an insertion, deletion and / orreplacement of one or more nucleotides into the transcribed region or coding of the gene, leadingto a reduced function or preferably loss of function LsPhyB protein, resulting in e.g. a loss-of- function (or reduced function) of the protein and at least delayed bolting and / or shade tolerance when the allele is in homozygous form (when no wild type allele is present in the diploid plant or plant cell).In one aspect, at least one amino acid of the conserved PAS2-domain or preceding the conservedPAS2-domain is deleted, inserted and / or replaced by another amino acid or by a STOP codon orone or more amino acids of the PAS2-domain or preceding the PAS2 domain are not transcribedand translated due to an insertion, deletion and / or replacement of one or more nucleotides into the allele, resulting in e.g. a loss-of-function (or reduced function) of the protein and at least delayed bolting and / or shade tolerance when the allele is in homozygous form (when no wild type allele is present in the diploid plant or plant cell). The wild type PAS2 domain is the domain starting at (and including) amino acid 752 and ending at (and including) amino acid 874 of SEQ ID NO: 1 or the equivalent amino acids of a wild type protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1. In one aspect the mutant allele encodes a protein which lacks at least one or more (or all) aminoacid of the PAS2 domain of SEQ ID NO: 1 (which PAS2 domain starts at amino acid 752 andends at amino acid 874 of SEQ ID NO: 1, or the equivalent amino acid of a sequence comprising at least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQ ID NO: 1) or wherein one or more amino acids of the PAS2-domain are replaced by one or more different amino acid or are missing, e.g. due to a stop codon mutation in a codon preceding the codons ofthe PAS2-domain or in a codon of the PAS2-domain or due to an insertion, deletion and / orreplacement of one or more nucleotides into the transcribed region or coding of the gene, leadingto a reduced function or preferably loss of function LsPhyB protein, resulting in e.g. a loss-of- function (or reduced function) of the protein and at least delayed bolting and / or shade tolerance when the allele is in homozygous form (when no wild type allele is present in the diploid plant or plant cell).In one aspect, at least one amino acid of the conserved HKRD-domain or preceding theconserved HKRD-domain is deleted, inserted and / or replaced by another amino acid or by aSTOP codon or one or more amino acids of the HKRD -domain or preceding the HKRD domainare not transcribed and translated due to an insertion, deletion and / or replacement of one or more nucleotides into the allele, resulting in e.g. a loss-of-function (or reduced function) of the protein and at least delayed bolting and / or shade tolerance when the allele is in homozygous form (when no wild type allele is present in the diploid plant or plant cell).Nunhems Netherlands B.V. 240134WO0111The wild type HKRD- domain is the domain starting at (and including) amino acid 896 and endingat (and including) amino acid 960 of SEQ ID NO: 1 or the equivalent amino acids of a wild type protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1. In one aspect the mutant allele encodes a protein which lacks at least one or more (or all) aminoacid of the HKRD-domain of SEQ ID NO: 1 (which HKRD-domain starts at amino acid 896 andends at amino acid 960 of SEQ ID NO: 1, or the equivalent amino acid of a sequence comprisingat least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQ ID NO: 1) or wherein one or more amino acids of the HKRD -domain are replaced by one or more different amino acid or are missing, e.g. due to a stop codon mutation in a codon preceding the codons ofthe HKRD -domain or in a codon of the HKRD -domain or due to an insertion, deletion and / orreplacement of one or more nucleotides into the transcribed region or coding region of the gene,leading to e.g. a reduced function or preferably loss of function LsPhyB protein and at leastdelayed bolting and / or shade tolerance when the allele is in homozygous form (when no wild type allele is present in the diploid plant or plant cell).In one aspect, at least one amino acid of the conserved HATPase Phy-like -domain or precedingthe conserved HATPase Phy-like -domain is deleted, inserted and / or replaced by another aminoacid or by a STOP codon or one or more amino acids of the HATPase Phy-like -domain orpreceding the HATPase Phy-like domain are not transcribed and translated due to an insertion, deletion and / or replacement of one or more nucleotides into the allele, resulting in e.g. a loss-of- function (or reduced function) of the protein and at least delayed bolting and / or shade tolerance when the allele is in homozygous form (when no wild type allele is present in the diploid plant or plant cell).The wild type HATPase Phy-like - domain is the domain starting at (and including) amino acid1007 and ending at (and including) amino acid 1119 of SEQ ID NO: 1 or the equivalent amino acids of a wild type protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1. In one aspect the mutant allele encodes a protein which lacks at least one or more (or all) aminoacid of the HATPase Phy-like -domain of SEQ ID NO: 1 (which HATPase Phy-like -domain startsat amino acid 1007 and ends at amino acid 1119 of SEQ ID NO: 1, or the equivalent amino acidof a sequence comprising at least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQ ID NO: 1) or wherein one or more amino acids of the HATPase Phy-like -domain are replaced by one or more different amino acid or are missing, e.g. due to a stop codon mutation in a codon preceding the codons of the HATPase Phy-like -domain or in a codon of the HATPasePhy-like -domain or due to an insertion, deletion and / or replacement of one or more nucleotidesinto the transcribed region of the gene, leading to e.g. a reduced function or preferably loss offunction LsPhyB protein and at least delayed bolting and / or shade tolerance when the allele is inhomozygous form (when no wild type allele is present in the diploid plant or plant cell).In one aspect the mutant allele encodes a PhyB protein which is truncated, missing at least 50,60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 215, 220, 230, 240, 249, 250, 251, 252, 255, 260, 261, 262, 263, 264, 265, 300, 350, 360, 370, 374, 375, 376, 377, 378, 379, 380, 381, 382, 385, 390,395, 400, 450, 500, 501, 502, 503, 504 or more amino acids of the C-terminal end of the wild typePhyB protein of SEQ ID NO: 1 (or of a wild type protein comprising at least 95%, 96%, 97%, 98%Nunhems Netherlands B.V. 240134WO0112or 99% identity to SEQ ID NO: 1), especially wherein said missing amino acids are consecutiveamino acids. Optionally the missing wild type amino acids may be replaced by one or more different amino acids, wherein the mutant allele results in delayed bolting and / or shade tolerance when the mutant allele is in homozygous form.In other words, the truncated mutant protein may comprise the N-terminal amino acids comprisingthe GAF-domain and Phy-domain and lack one or more or all of the C-terminal amino acids comprising the Modulator Loop domain, the PAS1-domain, the PAS2-domain, the HKRD-domain and the HATPase Phy-like domain.A loss-of-function of the protein (or a reduced function) is present when the mutant allele changesthe in vivo phenotype from the wild type phenotype, i.e. normal bolting and Shade avoidancesymptoms when the wild type allele is present in homozygous form, into delayed bolting and / orshade tolerance when the mutant allele is in homozygous form in a diploid plant.The equivalent amino acids in a sequence comprising at least 95%, 96%, 97%, 98% or 99% or more sequence identity to SEQ ID NO: 1 can be identified by pairwise alignment (e.g. using the program Needle) with SEQ ID NO: 1. Likewise the equivalent nucleotide in a sequence comprising at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more sequence identity toSEQ ID NO: 5 (or other sequences herein e.g. SEQ ID NO: 3 or 7) can be identified by pairwisealignment (e.g. using the program Needle) with SEQ ID NO: 5 (or with other sequences herein,accordingly, such as SEQ ID NO: 3 or 7).In one aspect Q750 of the PhyB protein of SEQ ID NO: 1 (or the equivalent amino acid in asequence comprising at least 95%, 96%, 97%, 98%, 99% or more sequence identity to SEQ IDNO: 1), is replaced by a different amino acid, is deleted or is replaced by a stop codon. In another aspect the Q91, the W369, the W524, the Q549, the Q612 or the E707 of the PhyB protein of SEQ ID NO: 1 (or the equivalent amino acid in a sequence comprising at least 95%,96%, 97%, 98%, 99% or more sequence identity to SEQ ID NO: 1), is replaced by a differentamino acid, is deleted or is replaced by a stop codon. Also provided is a Lactuca sativa plant or plant part comprising in its genome at least one copyof a mutant allele of the Phytochrome B (LsPhyB) gene, wherein the mutant allele encodes amutant protein wherein at least one amino acid in the Modulator Loop domain or at least oneamino acid preceding the Modulator Loop domain, starting at amino acid 745 of SEQ ID NO: 1and ending at amino acid 765 of SEQ ID NO: 1, is replaced by a different amino acid or by aSTOP codon or is deleted and wherein the mutant allele delays the start of bolting of the Lactucasativa plant by at least 7, 8, 9, 10, 11, 12, 13, 14 or more days and / or wherein the mutant allelecauses shade tolerance when the mutant allele is present in homozygous form, compared to thecontrol plant lacking the mutant allele, wherein the wild type allele encodes the protein of SEQ IDNO: 1 (or a protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1). The plant may either be heterozygous for the mutant allele, or homozygous for the mutant allele.Furthermore, a Lactuca sativa plant or plant part is encompassed, comprising in its genome atleast one copy of a mutant allele of the Phytochrome B (LsPhyB) gene, wherein the mutant alleleencodes a truncated protein wherein the truncation starts at an amino acid in a domain selectedfrom the PAS1-domain, the Modulator loop domain, the PAS2 domain, the HKRD domain or theNunhems Netherlands B.V. 240134WO0113 HATPAse Phy-like domain, or wherein the truncation starts at an amino acid preceding theModulator loop domain or preceding the PAS2 domain, and wherein the mutant allele delays thestart of bolting of the Lactuca sativa plant by at least 7, 8, 9, 10, 11, 12, 13, 14 or more daysand / or wherein the mutant allele causes shade tolerance when the mutant allele is present inhomozygous form, compared to the control plant lacking the mutant allele, wherein the wild typeallele encodes the protein of SEQ ID NO: 1 (or a protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1). The plant may either be heterozygous for the mutant allele, or homozygous for the mutant allele.In a different aspect a Lactuca sativa plant or plant part is encompassed, comprising in its genomeat least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene, wherein the mutantallele comprises at least one or more nucleotides inserted, deleted and / or replaced in the promoter region of the wild type LsPhyB gene thereby causing reduced expression of the LsPhyBgene or no expression of the LsPhyB gene and wherein the mutant allele delays the start ofbolting of the Lactuca sativa plant by at least 7, 8, 9, 10, 11, 12, 13, 14 or more days and / orwherein the mutant allele causes shade tolerance when the mutant allele is present in homozygous form, compared to the control plant lacking the mutant allele. The wild type allele of the LsPhyB gene encodes the protein of SEQ ID NO: 1 (or a protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1). The promoter region is the region of SEQ ID NO: 7 or a promoter region comprising at least 95%, 96%, 97%, 98% or 99% sequenceidentity to SEQ ID NO: 7. Reduced gene expression of the mutant promoter region refers to equalto or less than 50% of (wild type) mRNA transcript being made compared to the mRNA level expressed by the wild type allele (by the wild type promoter), preferably to equal to or less than40% of wild type allele mRNA levels, or equal to or less than 30% of wild type allele mRNA levels,or equal to or less than 20%, 10%, 5%, 3%, 2% or 1% of wild type allele mRNA levels. Wild type mRNA sequence encoding the wild type protein of SEQ ID NO: 1 is shown in SEQ ID NO: 3 (as cDNA). For wild type mRNA encoding a variant wild type protein which comprises at least 95% sequence identity to SEQ ID NO: 1 the wild type mRNA comprises at least 95% sequence identity to SEQ ID NO: 3. The plant may either be heterozygous for the mutant allele, or homozygous for the mutant allele.In addition, a seed from which the Lactuca sativa plant as provided herein can be grown. Furtherprovided is a plant cell, tissue or plant part of the Lactuca sativa plant or of the seed comprisingthe mutant allele of the LsPhyB gene, as described herein, in heterozygous or preferably inhomozygous form. In addition, a method for producing harvested plant material, such as lettuce heads or leaves, is provided herein, said method comprising growing a Lactuca sativa plant or seed as described,preferably comprising the mutant allele in homozygous form, and harvesting the lettuce head orleaves produced by said Lactuca sativa plant. In addition, a method for identifying and / or selecting a Lactuca sativa plant or plant part comprisesin its genome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene is providedherein, wherein the mutant allele encodes a mutant PhyB protein as described elsewhere herein or wherein the mutant allele comprises a mutant promoter causing no expression or reduced expression of the gene, said method comprising analysing the genomic DNA for the presence of the mutant allele, e.g. using a PCR method, a SNP genotyping method or sequencing.Nunhems Netherlands B.V. 240134WO0114 In addition, a method for identifying and / or selecting a Lactuca sativa plant or plant part comprisesin its genome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene is providedherein, wherein the mutant allele encodes a truncated protein or a mutant protein (comprising e.g.one or more amino acids inserted, replaced and / or deleted compared to the wild type protein) as described elsewhere herein, or wherein the mutant allele comprises a mutant promoter as described elsewhere herein, and wherein the mutant allele delays the start of bolting of theLactuca sativa plant by at least 7, 8, 9, 10, 11, 12, 13, 14 or more days and / or wherein the mutantallele causes shade tolerance when the mutant allele is present in homozygous form, comparedto the control plant lacking the mutant allele, wherein the wild type allele encodes the protein ofSEQ ID NO: 1 (or a protein comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1), said method comprising analysing the genomic DNA for the presence of themutant allele, e.g. using a PCR-based method, a SNP genotyping method or sequencing.In addition, a method for producing or generating a Lactuca sativa plant comprising a mutantallele which delays bolting of said plant and / or confers shade tolerance to said plant when presentin homozygous form is provided herein, said method comprising the step(s) of: (i) crossing a firstLactuca sativa plant and a second plant, wherein the first Lactuca sativa plant comprises in itsgenome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene, wherein themutant allele encodes a mutant protein or a mutant promoter as described elsewhere herein; andoptionally (ii) harvesting seed from the crossing of (i), and optionally (iii) selecting seed comprisingsaid mutant allele in its genome. In addition, a method for producing or generating a Lactuca sativa plant comprising a mutantallele which delays bolting and / or causes shade tolerance of said plant when present inhomozygous form is provided herein, said method comprising the step(s) of: (i) crossing a firstLactuca sativa plant and a second plant, wherein the first Lactuca sativa plant comprises in itsgenome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene, wherein the mutant allele encodes a mutant protein or a mutant promoter as described elsewhere herein, and wherein the mutant allele delays the start of bolting of the Lactuca sativa plant by at least 7, 8, 9,10, 11, 12, 13, 14 or more days and / or wherein the mutant allele causes shade tolerance whenthe mutant allele is present in homozygous form, compared to the control plant lacking the mutantallele, wherein the wild type allele encodes the protein of SEQ ID NO: 1 (or a protein comprisingat least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1), and optionally (ii)harvesting seed from the crossing of (i), and optionally (iii) selecting seed comprising said mutant allele in its genome. BRIEF DESCRIPTION OF THE FIGUREFigure 1: Picture depicting the comparison of shoot apical meristem / flowering primordia intransversely cut lettuce head (at 52 DAS grown under the same conditions) showing at the topthe parents made to generate the F2 population (parents: WENDEL-325-1-7 mutant homozygous for the Q750STOP mutant and variety ‘Maurice’ homozygous for the wild type LsPhyB gene) and four F2 lettuce heads, three started bolting and comprise the LsPhyB wild type gene and one (left hand bottom corner) is labelled as ‘slow’ bolting / delayed bolting and has not started bolting and comprises the Q750STOP LsPhyB mutant allele in homozygous form. DAS = Days After Sowing.Figure 2: Picture depicting the comparison of shoot apical meristem / flowering primordia intransversely cut lettuce head (at 52 DAS grown under the same conditions) showing at the topNunhems Netherlands B.V. 240134WO0115 the parents made to generate the F2 population (parents: WENDEL-325-1-7 mutant homozygous for the Q750STOP mutant and variety ‘Fidel’ homozygous for the wild type LsPhyB gene) and four F2 lettuce heads, three started bolting and comprise the LsPhyB wild type gene and one (left hand bottom corner) is labelled as ‘slow’ bolting / delayed bolting and has not started bolting and comprises the Q750STOP LsPhyB mutant allele in homozygous form. Figure 3: Pairwise amino acid sequence alignment made by Emboss-Needle of SEQ ID NO: 8 (wild type cucumber CsPhyB protein) and SEQ ID NO: 1 (wild type lettuce LsPhyB protein). The N-terminal part of the protein starts at amino acid 1 and ends at the end of the conserved Phy- domain. The N-terminal part comprises the conserved GAF-domain and the conserved Phy- domain. The C-terminal part of the protein starts at the end of the Phy-domain and runs until the end of the protein. The C-terminal part comprises the conserved Modulator Loop domain (shaded in grey), the conserved PAS1-domain, the conserved PAS2-domain, the conserved HKRD- domain and the conserved HATPase Phy-like domain. Figure 4: Foto comparing seedling height and internode length of the wild type (left) and homozygous Q750STOP mutant (right) at 35 DAS and grown at a density of 200 plants per m2with FarRed light supplementation (White light +FR (R:FR = 0.4), see Examples). The mutantdoes not respond by an extension of internode length and does not respond by an increase inplant height under these conditions, showing that the mutant is shade tolerant, while the wild typedoes show the expected shade avoidance response.Figure 5: Foto comparing seedling height and internode length of the wild type (left) and homozygous Q750STOP mutant (right) at 35 DAS and grown at a density of 400 plants per m2with FarRed light supplementation (White light +FR (R:FR = 0.4), see Examples). The mutantdoes not respond by an extension of internode length and does not respond by an increase inplant height under these conditions, showing that the mutant is shade tolerant, while the wild typedoes show the expected shade avoidance response.Figure 6: Foto (taken 8 days after sowing) comparing hypocotyl length of the wild type (top row)and homozygous Q750STOP mutant (bottom row) of seedlings grown under white light (withR:FR = 1.0) or under shade stress conditions (with R:FR = 0.4), see Examples. The wild typeresponds to the shade stress by hypocotyl elongation, while the mutant is unresponsive and haselongated hypocotyls under both light conditions, showing that the mutant is shade tolerant, whilethe wild type does show the expected shade avoidance response.Figure 7: AlphaFold2 image of the wild type LsPhyB protein of SEQ ID NO: 1, whereby the C- terminal region which is absent in the Q750* mutant protein is visualized by the darker grey parts of the protein. DETAILED DESCRIPTION General definitions It is to be understood that this invention is not limited to the particular methodology or protocols. It is also to be understood that the terminology used herein is for the purpose of describingparticular embodiments only and is not intended to limit the scope of the present invention whichwill be limited only by the appended claims. It must be noted that as used herein and in the appended claims, the singular forms "a," "and," and "the" include plural reference unless theNunhems Netherlands B.V. 240134WO0116 context clearly dictates otherwise. Thus, for example, reference to "a vector" is a reference to one or more vectors and includes equivalents thereof known to those skilled in the art, and so forth. The term "about" is used herein to mean approximately, roughly, around, or in the region of. When the term "about" is used in conjunction with a numerical range, it modifies that range by extending the boundaries above and below the numerical values set forth. In general, the term "about" is used herein to modify a numerical value above and below the stated value by a variance of 10 percent, preferably 5 percent, 3 percent, 2percent or 1 percent up or down (higher or lower). As used herein, the word "or" means any one member of a particular list and also includes any combination of members of that list. The words "comprise," "comprising," "include," "including," and "includes" when used in this specification and in the following claims are intended to specify the presence of one or more stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, or groups thereof. For clarity, certain terms used in the specification are defined and used as follows: The term "genome" relates to the genetic material of an organism. It consists of DNA. The genomeincludes both the genes and the non-coding sequences of the DNA. The Lactuca sativa wild typeLsPhyB gene is located on chromosome 1 in the genome Lsat_Salinas_v11 at nucleotide position51203069 to 51198893, as detected by BLAST analysis of SEQ ID NO: 5 against theLsat_Salinas_v11 genome (found on the world wide web at ncbi.nlm.nih.gov / datasets / genome / ?taxon=4236). The term "gene" means a (genomic) DNA sequence comprising a region (transcribed region), which is transcribed into a messenger RNA molecule (mRNA) in a cell, and an operably linked regulatory region (also described herein as regulatory sequence, e.g. a promoter). A gene may thus comprise several operably linked sequences, such as a promoter, a 5' leader sequence comprising e.g. sequences involved in translation initiation, a (protein) coding region (cDNA or genomic DNA) and a 3' non-translated sequence comprising e.g. transcription termination sites. Different alleles of a gene are thus different alternative forms of the gene, which may be in the form of e.g. differences in one or more nucleotides of the genomic DNA sequence (e.g. in the promoter sequence, the exon sequences, intron sequences, etc.), mRNA and / or amino acid sequence of the encoded protein. A gene may be an endogenous gene (in the species of origin) or a chimeric gene (e.g. a transgene or cis-gene). The "promoter" of a gene sequence is defined as a region of DNA that initiates transcription of a particular gene. Promoters are located near the genes they transcribe, on the same strand and upstream on the DNA. Promoters can be about 100-1000 base pairs long. In one aspect the promoter is defined as the region of about 1000 base pairs or more e.g. about 1500 or 2000, upstream of the start codon (i.e. ATG) of the protein encoded by the gene. "Transgene" or "chimeric gene" refers to a genetic locus comprising a DNA sequence, such as a recombinant gene, which has been introduced into the genome of a plant by transformation, such as Agrobacterium mediated transformation. A plant comprising a transgene stably integrated into its genome is referred to as “transgenic plant”. "Expression of a gene" refers to a process wherein a DNA region, which is operably linked to appropriate regulatory regions, particularly a promoter, is transcribed into an RNA, which isNunhems Netherlands B.V. 240134WO0117 biologically active, i.e. which is capable of being translated into a biologically active protein or peptide or which is active itself (e.g. in posttranscriptional gene silencing or RNAi). The coding sequence may be in sense-orientation and encodes a desired, biologically active protein or peptide. The terms "protein" and "polypeptide" are used interchangeably and refer to molecules consisting of a chain of amino acids, without reference to a specific mode of action, size, 3 -dimensional structure or origin. A "fragment" or "portion" of a protein may thus still be referred to as a "protein". An "isolated protein" is used to refer to a protein which is no longer in its natural environment, forexample in vitro or in a recombinant bacterial or plant host cell.The terms “peptide sequence” and “amino acid sequence” refer to the primary amino acid sequence of a protein or polypeptide. The term "locus" (plural loci) means a specific place or places or a site on a chromosome where for example a gene or genetic marker is found. As is used herein, a QTL (quantitative trait locus) is a hereditary unit (often indicated by one or more molecular genomic markers) that occupies a specific location on a chromosome and that contains the genetic instruction for a particular phenotypic characteristics or trait in a plant. In contrast to a gene, the exact boundaries of a QTL are not known, but can be found without undueburden by a person skilled in the art by using fine mapping techniques well known in the art ofgenetic mapping and subsequent DNA sequencing routines. The QTL encodes at least one gene of which the expression, alone or in combination with other genes, results in the phenotypic trait being expressed, or that encodes at least one regulatory region that controls the expression of at least one gene the expression of which, alone or in combination with other genes, results in the phenotypic trait being expressed. A QTL may be defined by indicating its genetic location in the genome of the donor of the introgression that contains the QTL using one or more molecular genomic markers. These one or more markers, in turn, indicate a specific locus. Distances between loci are usually measured by frequency of crossing-over between loci on the same chromosome. The further apart two loci are, the more likely that a crossover will occurbetween them. Conversely, if two loci are close together, a crossover is less likely to occurbetween them. As a rule, one centimorgan (cM) is equal to 1% recombination between loci (markers). When a QTL can be indicated by multiple markers the genetic distance between the end-point markers is indicative of the size of the QTL. Markers that define the QTL may be markers that are linked to the QTL or markers that are in linkage disequilibrium with the QTL. The term "allele(s)" means any of one or more alternative forms of a gene at a particular locus, all of which alleles relate to one trait or characteristic at a specific locus. In a diploid cell of an organism, alleles of a given gene are located at a specific location, or locus (loci plural) on a chromosome. One allele is present on each chromosome of the pair of homologous chromosomes. A diploid plant species may comprise a large number of different alleles at a particular locus. These may be identical alleles of the gene (homozygous) or two different alleles (heterozygous). An allelism test is a test known in the art that can be used to identify whether two genes conferring the same trait are located at the same locus.Nunhems Netherlands B.V. 240134WO0118 "Wild type allele" (WT) refers herein to a version of a gene encoding a fully functional protein (wildtype protein). Accordingly, the term "wild type LsPhyB allele" or "PhyB allele" or "wild type alleleof the Phytochrome B gene or "wild type allele of the PhyB gene" refers to the fully functionalallele of the Phytochrome B gene, which allows the normal bolting and flowering during plantdevelopment and / or the development of one or more symptoms of Shade Avoidance Syndrome.Such a wild type PhyB allele in the species Lactuca sativa for instance is the wild type genomicDNA which encodes the wild type PhyB cDNA (mRNA) sequence depicted in SEQ ID NO: 3. Theprotein sequence encoded by this wild type Lactuca sativa PhyB cDNA has 1125 amino acidsand is depicted in SEQ ID NO: 1, which corresponds to NCBI reference sequenceXP_023763453.1 derived from gene with ID: 111911925 (LOC111911925). The wild type PhyBallele further comprises functional variants of the wild type genomic DNA (SEQ ID NO: 5) whichencodes the wild type PhyB cDNA and amino acid sequences as described herein, such asfunctional PhyB proteins comprising at least 95%, 96%, 97%, 98%, 99% or more amino sequenceidentity to SEQ ID NO: 1. Whether a certain variant of the herein specifically described wild type PhyB allele represents a functional variant can be determined by using routine methods,including, but not limited to, phenotypic testing for normal bolting behaviour during plantdevelopment and / or symptoms of Shade Avoidance during treatment such as shade, growing athigh density or light induced stress by e.g. supplementation with FarRed light.“Shade Avoidance Syndrome (SAS)” or “SAS symptoms” or “Shade Avoidance symptoms” refersto one or more symptoms seen in lettuce plants comprising a wild type PhyB gene in homozygousform (also referred to as ‘wild type’ plants) when grown e.g. under light stress or density stress conditions, such as low Red:FarRed ratios (e.g. R:FR is equal to or less than 0.4, 0.3, 0.2 or 0.1 or less) simulating shade and / or high seedling densities causing shade, whereby the ShadeAvoidance symptoms are longer internodes (elongations of the internodes) and / or taller / higherplants, optionally also longer leaves. “Shade tolerance” or “shade tolerant” refers to the lettuce plant not showing (or showing to asignificant less extent than the wild type plant) the one or more or all of the Shade Avoidancesymptoms when grown under the same conditions under which the wild type plant shows theShade Avoidance symptoms, such as internode elongation and / or increased plant height.“Light stress” or “density stress” and / or “shade stress” refers to growing conditions which trigger one or more Shade Avoidance symptoms in wild type lettuce plants, such as growing seedlings at high densities (e.g.200 or more seedlings per square meter) and / or at low R:FR light ratios, e.g. R:FR is equal to or less than 0.6, 0.5, 0.4, 0.3, 0.2 or 0.1 or less.“N-terminal region” of the LsPhyB protein starts at (and including) amino acid 1 and ends at (andincluding) amino acid 593 of SEQ ID NO: 1 or the equivalent amino acid in a wild type PhyB protein sequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1. The N-terminal region contains the GAF domain (cGMP phosphodiesterase, Adenylylcyclase, Fh1A) and Phy-domain (Phytochrome specific) and is the photosensory module of theprotein. “C-terminal region” of the LsPhyB protein starts at (and including) amino acid 594 and ends at (and including) amino acid 1125 of SEQ ID NO: 1 or the equivalent amino acid in a wild type PhyB protein sequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1. The C-terminal region is involved in e.g. dimerization of PhyB proteins and downstreamNunhems Netherlands B.V. 240134WO0119 processes such as interaction with PIF (Phy-interacting) transcription regulators. The C-terminal includes a PAS1 domain, a Modulator Loop domain, a PAS2 domain, a HKRD domain and a HATPase Phy-like domain.“PAS1 domain” (PER, ARNT, SYM domain) of the LsPhyB protein starts at (and including) aminoacid 622 and ends at (and including) amino acid 739 of SEQ ID NO: 1 or the equivalent amino acid in a wild type PhyB protein sequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1.“Modulator Loop domain” of the LsPhyB protein starts at (and including) amino acid 745 and endsat (and including) amino acid 765 of SEQ ID NO: 1 or the equivalent amino acid in a wild type PhyB protein sequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1.“PAS2 domain” (PER, ARNT, SYM domain) of the LsPhyB protein starts at (and including) aminoacid 752 and ends at (and including) amino acid 874 of SEQ ID NO: 1 or the equivalent amino acid in a wild type PhyB protein sequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1.“HKRD domain” (histidine kinase related domain) of the LsPhyB protein starts at (and including)amino acid 896 and ends at (and including) amino acid 960 of SEQ ID NO: 1 or the equivalentamino acid in a wild type PhyB protein sequence comprising at least 95%, 96%, 97%, 98% or99% sequence identity to SEQ ID NO: 1.“HATPase Phy-like domain” (histidine kinase-like ATPase domain) of the LsPhyB protein startsat (and including) amino acid 1007 and ends at (and including) amino acid 1119 of SEQ ID NO: 1 or the equivalent amino acid in a wild type PhyB protein sequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1. "Mutant allele" refers herein to an allele that encodes a mutant protein comprising one or more amino acids replaced, inserted and / or deleted with respect to the wild type protein and resulting in delayed bolting and / or shade tolerance when the mutant allele is in homozygous form. Such a mutant allele accordingly can refer to an allele comprising one or more mutations in thetranscribed region or coding sequence (mRNA, cDNA or genomic sequence) compared to thewild type allele or one or more mutations in the promoter region compared to the wild type allele.Such mutation(s) (e.g. insertion, deletion and / or replacement of one or more nucleotide(s)) maylead to the encoded protein having reduced in vivo functionality (reduced function) or no in vivofunction (loss-of-function) e.g. due to the protein or having an amino acid sequence wherein one or more amino acids are deleted, inserted and / or replaced; or (in case of a mutant promoter of the allele) to the mutant allele not being expressed or being expressed to a reduced extent than the wild type allele. Such changes may lead to the mutant protein having a different 3Dconformation and / or interaction (e.g. no dimerization or unstable dimerization), being targeted toa different sub-cellular compartment, having a modified catalytic domain, having a modifiedbinding activity to nucleic acids or proteins, etc. Mutant alleles can be generated de novo bymutagenesis methods, such as chemical mutagenesis (e.g. using EMS or MNU mutagenesis or mutagenesis by generating reactive oxygen species) or radiation mutagenesis (e.g. using UVradiation or ion beam radiation) or targeted gene editing methods. Accordingly, "mutant LsPhyBallele" or "phyb allele" or "mutant allele of the Phytochrome B gene" or "mutant allele of the PhyBNunhems Netherlands B.V. 240134WO0120gene" refers to an allele of the Phytochrome B gene (PhyB gene) comprising one or moremutations leading to one or more amino acids being replaced, deleted and / or inserted compared to the wild type protein, which mutant allele delays bolting and / or causes shade tolerance of theLactuca sativa plant when the mutant allele is in homozygous form; or comprising one or morenucleotides in the promoter region being replaced, deleted and / or inserted compared to the wildtype promoter region, which mutant allele delays bolting and / or causes shade tolerance of theLactuca sativa plant when the mutant allele is in homozygous form. Preferably, the term mutantPhyB allele as used herein refers herein to a mutant PhyB allele which is not found in plants in the natural population or breeding population, but which is produced by human intervention such as mutagenesis or targeted gene modification (also referred to as targeted gene editing), such as effected through e.g. CRISPR / Cas9, CRISPR / Cpf1 or similar methods. Herein the term “mutant allele” therefore does in one aspect also encompass mutant alleles which have mutations inregulatory elements, especially in the promoter region of the LsPhyB gene, and therefore havereduced gene expression or no gene expression, leading to reduced amount of wild type PhyBprotein or no wild type PhyB protein being produced in vivo and resulting in delayed bolting and / orshade tolerance when the mutant allele is in homozygous form. An “active protein” or “functional protein” or “wild type protein” is a protein which has normal (i.e.not reduced) protein activity as measurable in vitro, e.g. by an in vitro activity assay, and / or invivo, e.g. by the phenotype conferred by the protein. A “wild type” PhyB protein is a functional protein of SEQ ID NO: 1 or a functional wild type protein comprising at least 95%, 96%, 97%,98% or 99% amino acid sequence identity to SEQ ID NO: 1 (also referred to as a ‘variant’ of SEQID NO: 1) when aligned pairwise (e.g. using the program Needle, default parameters). Likewise,the wild type PhyB allele is the allele encoding a wild type protein or variant. In a Lactuca sativaplant the wild type PhyB gene encodes a protein of SEQ ID NO: 1 or a functional proteincomprising at least 95%, 96%, 97%, 98% or 99% amino acid sequence identity to SEQ ID NO: 1.A "mutant protein" is herein a protein comprising one or more amino acids inserted, deleted and / orreplaced with respect to the wild type protein, due to mutations in the genomic DNA encoding theprotein. In one aspect the mutant protein has a reduced function or loss-of-function, e.g.measurable in vivo, e.g. by the phenotype conferred by the mutant allele, for example delayed bolting and / or shade tolerance when the mutant allele is in homozygous form compared to a control plant which lacks the mutant allele. “Mutant proteins” thus comprise “reduced-function” or “loss-of-function” proteins, as e.g. measurable in vivo, e.g. by the phenotype conferred by themutant allele in homozygous form, e.g. in a phenotypic test to determine the bolting behaviourduring plant development and / or to determine whether the plant is shade tolerant.A "Phytochrome B protein having a Q750* mutation" or a “PhyB protein having a Q750* mutation”or a “PhyB protein having a Q750STOP mutation” refers to an Lactuca sativa PhyB protein ofSEQ ID NO: 1, or variant thereof comprising at least 95%, 96%, 97%, 98% or 99% amino acidsequence identity to SEQ ID NO: 1, that is truncated due to the codon for amino acid 750 of SEQID NO: 1, or for the equivalent amino acid position in a wild type PhyB protein comprising at least95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1, being changed into a STOPcodon. One example of a PhyB protein having a Q750* mutation is the Lactuca sativa PhyBprotein of SEQ ID NO: 1 that is truncated due to a mutation of codon 750 into a STOP codon. Thetruncated Q750* protein is shown in SEQ ID NO: 2. In the wild type genomic sequence of SEQID NO: 5, the codon is at nucleotides 2888 to 2890 of SEQ ID NO: 5 (codon CAA, encoding Q) ismutated to TAA, which is a STOP codon. This mutant has delayed bolting when in homozygousNunhems Netherlands B.V. 240134WO0121form and shows shade tolerance (see Examples). Similarly, a phytochrome B protein having aSTOP mutation for a certain amino acid codon refers to an Lactuca sativa PhyB protein of SEQID NO: 1, or variant thereof comprising at least 95%, 96%, 97%, 98% or 99% amino acidsequence identity to SEQ ID NO: 1, that is truncated due to the codon for that amino acid of SEQID NO: 1, or for the equivalent amino acid position in a wild type PhyB protein comprising at least95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1, being changed into a STOPcodon.When referring to an amino acid “at the equivalent amino acid position in a wild type PhyB proteincomprising e.g. at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1”, the equivalent amino acid in a variant protein is referred to. The equivalent amino acid can easily be identified by pairwise alignment of the variant sequence with the sequence of SEQ ID NO: 1. Due to the high percentage of sequence identity, the equivalent amino acid position will be immediatelyapparent. The Q at position 750 of SEQ ID NO: 1 may for example be located at position 748,749, 751 or 752 in a variant protein comprising at least 95% identity to SEQ ID NO: 1."Wild type plant" refers herein to a Lactuca sativa plant comprising two copies of the wild type PhyB allele (encoding the wild type protein of SEQ ID NO: 1 or a variant functional wild typeprotein comprising at least 95% to SEQ ID NO: 1) showing normal bolting and symptoms of ShadeAvoidance. Such plants are for example suitable controls in phenotypic assays.“Control plant” is a plant genotype comprising two copies of the wild type PhyB allele, encodingwild type, functional PhyB protein, which can be suitably used in a phenotyping assay, e.g. tocompare the start of bolting and / or shade tolerance symptoms (see e.g. Examples) between thecontrol plant and a plant homozygous for a mutant phyB allele. Preferably the control plant is ofthe same type as the plant comprising the mutant allele in homozygous form (e.g. both are butterhead types or both are Romaine types). Preferably the control plant comprising the wildtype PhyB allele in homozygous form is genetically very similar to the plant comprising the mutantphyB allele in homozygous form, so that the differences in bolting and / or shade tolerance arecompared in the same or similar genetic backgrounds. The control plant may, thus, be e.g. a nearisogenic line or isogenic line or a so-called ‘genetic control’ line. For example, a mutant allele maybe crossed into a specific lettuce line or variety and the original line or variety, or a backcross linelacking the mutant allele may be used as control.The word "trait" in the context of this application refers to the phenotype of the plant. When a plant shows the traits, its genome comprises the mutant allele causing the trait, particularly when themutant allele is in homozygous form. The plant, thus, has the genetic determinant for the trait. Itis understood that when referring to a plant comprising the trait, reference is made to a Lactucasativa plant comprising the trait of delayed bolting and / or shade tolerance (compared to thecontrol plant having two copies of the wild type PhyB allele)."Average" refers herein to the arithmetic mean.As used herein, the term “molecular genomic marker” or short “marker” or “DNA marker” refers toan indicator that is used in methods for visualizing differences in characteristics of nucleic acidsequences, especially different alleles (also referred to as ‘allele specific markers’). Examples ofsuch indicators are restriction fragment length polymorphism (RFLP) markers, amplified fragment length polymorphism (AFLP) markers, single nucleotide polymorphisms (SNPs), insertionNunhems Netherlands B.V. 240134WO0122 mutations, microsatellite markers (SSRs), sequence-characterized amplified regions (SCARs), cleaved amplified polymorphic sequence (CAPS) markers or isozyme markers or combinations of the markers described herein which defines a specific genetic and chromosomal location.Examples of SNPs are for example the C at nucleotide position 2888 of SEQ ID NO: 5 (wild typegenomic DNA) and the T at position 2888 of SEQ ID NO: 6 (mutant genomic DNA), whereby theC / T SNP either detects the wild type (codon CAA, encoding a Q at amino acid 750) or mutantPhyB allele (codon TAA, encoding a STOP codon).A fragment of a mutant protein refers to any subset of the molecule. Variant peptides may be made by direct chemical synthesis, for example, using methods well known in the art. An analogue of a mutant protein refers to a non-natural protein substantially similar to either the entire protein or a fragment thereof. A "mutation" in a nucleic acid molecule is a change of one or more nucleotides compared to the wild type sequence, e.g. by replacement, deletion and / or insertion of one or more nucleotides. A "mutation" in an amino acid molecule making up a protein is a change of one or more amino acids compared to the wild type sequence, e.g. by replacement, deletion and / or insertion of one or more amino acids. Such a protein is then also referred to as a "mutant protein". A "point mutation" is the replacement of a single nucleotide, or the insertion or deletion of a single nucleotide. A "nonsense mutation" is a (point) mutation in a nucleic acid sequence encoding a protein, whereby a codon in a nucleic acid molecule is changed into a stop codon. This results in a pre- mature stop codon being present in the mRNA and results in translation of a truncated protein. Atruncated protein may have reduced function or loss-of-function.A "missense or non-synonymous mutation" is a (point) mutation in a nucleic acid sequence encoding a protein, whereby a codon is changed to code for a different amino acid. The resultingprotein may have reduced function or loss-of-function.A "splice-site mutation" is a mutation in a nucleic acid sequence encoding a protein, whereby RNA splicing of the pre-mRNA is changed, resulting in an mRNA having a different nucleotidesequence and a protein having a different amino acid sequence than the wild type. The resultingprotein may have reduced function or loss-of-function.A "frame shift mutation" is a mutation in a nucleic acid sequence encoding a protein by which the reading frame of the mRNA is changed, resulting in a different amino acid sequence. The resultingprotein may have reduced function or loss-of-function.A "deletion" in context of the invention shall mean that anywhere in a given nucleic acid sequence at least one nucleotide is missing compared to the nucleic sequence of the corresponding wild type sequence or anywhere in a given amino acid sequence at least one amino acid is missing compared to the amino acid sequence of the corresponding (wild type) sequence.Nunhems Netherlands B.V. 240134WO0123 A "truncation" shall be understood to mean that at least 50, 60, 70, 80, 90, 100, 200, 250, 300,350, 400, 450 or more amino acids at the C-terminus of the protein are missing compared to theamino acid sequence of the corresponding wild type protein, optionally there may be other aminoacids present following the last amino acid of the wild type sequence. For example, a frame shiftmutation can lead to different amino acids being present. It is understood that there are still 50, 60, 70, 80, 90, 100 or more amino acids of the wild type N-terminal present in a truncated protein. In one aspect the entire N-terminal region is still present in a truncated protein."Replacement" or "substitution" shall mean that at least one nucleotide in a nucleic acid sequenceor one amino acid in a protein sequence is different compared to the corresponding wild type nucleic acid sequence or the corresponding wild type amino acid sequence, respectively, due toe.g. an exchange of one or more nucleotides in the transcribed region or coding region of therespective protein. "Insertion" shall mean that the nucleic acid sequence or the amino acid sequence of a protein comprises at least one additional nucleotide or amino acid compared to the corresponding wildtype nucleic acid sequence or the corresponding wild type amino acid sequence, respectively."Pre-mature stop codon" in context with the present invention means that a stop codon is present in a coding sequence (cds) which is closer to the start codon at the 5’-end compared to the stop codon of a corresponding wild type coding sequence. A "mutation in a regulatory sequence", e.g. in mutation in a promoter region of a gene, is a change of one or more nucleotides in e.g. the promoter region compared to the wild type sequence, e.g.by replacement, deletion and / or insertion of one or more nucleotides in the promoter sequence,leading for example to a decreased (or reduced) amount or no mRNA transcript of the gene being made. A decreased (or reduced) amount of mRNA transcript is in one aspect equal to or less than 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2% or 1% of the mRNA transcript made by the wild type promoter sequence of the wild type allele. As used herein, the term "operably linked" refers to a linkage of polynucleotide elements in a functional relationship. A nucleic acid is "operably linked" when it is placed into a functionalrelationship with another nucleic acid sequence. For instance, a promoter, or rather a transcriptionregulatory sequence, is operably linked to a coding sequence if it affects the transcription of the coding sequence. Operably linked means that the nucleic acid sequences being linked are typically contiguous. “Sequence identity" can be determined by alignment of two peptide or two nucleotide sequences using global or local alignment algorithms. Sequences may then be referred to as "substantially identical" when they share at least a certain minimal percentage of sequence identity (as defined further below) after optimally alignment by, for example, the program GAP or BESTFIT or the Emboss program "Needle" (using default parameters, see below). These programs use the Needleman and Wunsch global alignment algorithm to align two sequences over their entire length, maximizing the number of matches and minimizing the number of gaps. Generally, the default parameters are used, with a gap creation penalty = 10 and gap extension penalty = 0.5 (both for nucleotide and protein alignments). For nucleotides the default scoring matrix used is DNAFULL and for proteins the default scoring matrix is Blosum62 (Henikoff & Henikoff, 1992,PNAS 89, 10915- 10919). Sequence alignments and scores for percentage sequence identityNunhems Netherlands B.V. 240134WO0124 may for example be determined using computer programs, such as EMBOSS (world wide web atebi.ac.uk / Tools / psa / emboss_needle / ). Alternatively, sequence identity may be determined bysearching against databases such as FASTA, BLAST, etc. Hits are preferably aligned pairwise tocompare sequence identity (e.g. using the program Needle), preferably over the full length of thesequences. As used herein, two nucleotide sequences have "substantial sequence identity" if the percentage sequence identity is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or more, preferably as determined over their entire lengths (as determined by Emboss "needle" usingdefault parameters, e.g. gap creation penalty = 10, gap extension penalty = 0.5, using scoringmatrix DNAFULL for nucleic acids).As used herein, two protein sequences have "substantial sequence identity" if the percentagesequence identity is at least 95%, 96%, 97%, 98%, 99%, or more, preferably as determined overtheir entire lengths (as determined by Emboss "needle" using default parameters, e.g. gapcreation penalty = 10, gap extension penalty = 0.5, using scoring matrix default scoring matrix is Blosum62). The term "hybridisation" as used herein is used to indicate hybridisation of nucleic acids at appropriate conditions of stringency as would be readily evident to those skilled in the artdepending upon the nature of the probe sequence and target sequences. Conditions ofhybridisation and washing are well known in the art, and the adjustment of conditions depending upon the desired stringency by varying incubation time, temperature and / or ionic strength of the solution are readily accomplished. See, for example, Sambrook, J. et al., Molecular Cloning: A Laboratory Manual, 2nd edition, Cold Spring Harbor Press, Cold Spring Harbor, New York, 1989.The choice of conditions is dictated by the length of the sequences being hybridised, in particular,the length of the probe sequence, the relative G-C content of the nucleic acids and the amount of mismatches to be permitted. Low stringency conditions are preferred when partial hybridisation between strands that have lesser degrees of complementarity is desired. When perfect or near perfect complementarity is desired, high stringency conditions are preferred. When reference is made to a nucleic acid sequence (e.g. DNA or genomic DNA) having "substantial sequence identity to" a reference sequence or having a sequence identity of at least 90%, e.g. at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.2%, 99.5%, 99.9% nucleic acid sequence identity to a reference sequence, in one embodiment said nucleotide sequence is considered substantially identical to the given nucleotide sequence and can be identified using stringent hybridisation conditions. In another embodiment, the nucleic acid sequence comprises one or more mutations compared to the given nucleotide sequence but still can be identified using stringent hybridization conditions. "Stringent hybridisation conditions" can be used to identify nucleotide sequences, which are substantially identical to a given nucleotide sequence. Stringent conditions are sequence dependent and will be different in different circumstances. Generally, stringent conditions are selected to be about 5°C lower than the thermal melting point (Tm) for the specific sequences at a defined ionic strength and pH. The Tm is the temperature (under defined ionic strength and pH) at which 50% of the target sequence hybridises to a perfectly matched probe. Typically stringent conditions will be chosen in which the salt concentration is about 0.02 molar at pH 7 and the temperature is at least 60°C. Lowering the salt concentration and / or increasing the temperature increases stringency. Stringent conditions for RNA-DNA hybridisations (Northern blots using aNunhems Netherlands B.V. 240134WO0125 probe of e.g.100 nucleotides) are for example those which include at least one wash in 0.2X SSC at 63°C for 20min, or equivalent conditions. Stringent conditions for DNA-DNA hybridisation (Southern blots using a probe of e.g.100 nucleotides) are for example those which include at least one wash (usually 2) in 0.2X SSC at a temperature of at least 50°C, usually about 55°C, for 20 min, or equivalent conditions. As used herein, the phrase "hybridizes” to a DNA or RNA molecule is used to indicate that a molecule recognizes and hybridizes to another nucleic acid molecule by base pairing, meaning that there is enough sequence similarity between the two nucleic acid molecules to effect hybridization under appropriate conditions. As used herein, the terms "introgression", "introgressed" and "introgressing" refer to both a natural and artificial process whereby a genomic fragment of one species, variety or cultivar, termed donor parent, is transduced into the genome of another species, variety or cultivar, termed recipient parent, for example by crossing the donor and recipient parent. The process may optionally be completed by backcrossing the resulting plants to the recipient parent, which is than termed recurrent parent. As used herein, the term “plant” includes the whole plant or any parts or derivatives thereof, such as plant organs (e.g., harvested or non-harvested fruits, leaves, seed, flowers, etc.), plant cells, plant protoplasts, plant cell or tissue cultures from which e.g. whole plants can be regenerated, plant calli, plant cell clumps, and plant cells that are intact in plants, or parts of plants, such as embryos, pollen, ovules, ovaries, fruits, harvested tissues or organs, such as harvested heads orharvested leaves or parts thereof, flowers, leaves, seeds, clonally propagated plants, roots, root-stocks, stems, root tips and the like. Also any developmental stage is included, such as seedlings, immature and mature, etc. The term "cultivar" (or “cultivated” plant) is used herein to denote a plant having a biological status other than a "wild" status, which "wild" status indicates the original non-cultivated, non- domesticated, or natural state of a plant or accession, and the term cultivated does not include such wild, or weedy plants. The term cultivar does include material with good agronomiccharacteristics, such as breeding material, research material, breeding lines, elite breeding lines,synthetic population, hybrid, founder stock / base population, inbred lines, cultivars (open pollinated of hybrid cultivar), segregating population, mutant / genetic stock, andadvanced / improved cultivar. The so-called heirloom varieties or cultivars, i.e. open pollinatedvarieties or cultivars commonly grown during earlier periods in human history and often adapted to specific geographic regions, are in one aspect encompassed herein as cultivated plants. In one embodiment the term cultivar also includes landraces, i.e. plants (or populations) selected and cultivated locally by humans over many years and adapted to a specific geographic environment and sharing a common gene pool. "Plant variety" is a group of plants within the same botanical taxon of the lowest grade known, which (irrespective of whether the conditions for the recognition of plant breeder’s rights are fulfilled or not) can be defined on the basis of the expression of characteristics that result from a certain genotype or a combination of genotypes, can be distinguished from any other group of plants by the expression of at least one of those characteristics, and can be regarded as an entity, because it can be multiplied without any change. Therefore, the term “plant variety” cannot be used to denote a group of plants, even if they are of the same kind, if they are all characterizedNunhems Netherlands B.V. 240134WO0126 by the presence of one locus or gene (or a series of phenotypical characteristics due to this single locus or gene), but which can otherwise differ from one another enormously as regards the other loci or genes. "Backcrossing" refers to a breeding method by which a (single) trait, such as the delayed bolting trait, can be transferred from one genetic background (also referred to as "donor" generally, but not necessarily, this is an inferior genetic background) into another genetic background (also referred to as "recurrent parent"; generally, but not necessarily, this is a superior genetic background). An offspring of a cross (e.g. an F1 plant obtained by crossing a first plant of a certainplant species comprising the mutant allele as described herein with a second plant of the sameplant species or of a different plant species that can be crossed with said first plant species wherein said second plant species does not comprise the mutant allele; or an F2 plant or F3 plant, etc., obtained by selfing the F1) is "backcrossed" to a parent plant of said second plant species. After repeated backcrossing, the trait of the donor genetic background, e.g. the delayed bolting trait, will have been incorporated into the recurrent genetic background. The terms "gene converted" or "conversion plant" or "single locus conversion" in this context refer to plants which are developed by backcrossing wherein essentially all of the desired morphological and / or physiological characteristics of the recurrent parent are recovered in addition to the one or more genes transferred from the donor parent. The plants grown from the seeds produced by backcrossing of the F1 plants with the second parent plant line is referred to as the "BC1 generation". Plants from the BC1 population may be selfed resulting in the BC1F2 generation or backcrossed again with the cultivated parent plant line to provide the BC2 generation. An "M1 population" is a plurality of mutagenized seeds / plants of a certain plant line. "M2, M3, M4, etc." refers to the consecutive generations obtained following selfing of a first mutagenized seed / plant (M1). “Lettuce” or “cultivated lettuce” or “cultivated Lactuca sativa” refers herein to plants of the speciesLactuca sativa L. (or seeds from which the plants can be grown), and parts of such plants, bredby humans for food and having good agronomic characteristics. This includes any cultivatedlettuce, such as breeding lines (e.g. backcross lines, inbred lines), cultivars and varieties of anytype. Generally heading and non-heading types of lettuce are distinguished. Heading types include for example crisphead, butterhead and Romaine (cos) types, while non-heading typesinclude leaf- types. Cultivated lettuce plants are not “wild lettuce” plants or “wild Lactuca” plants,i.e. plants which generally have much poorer yields and poorer agronomic characteristics than cultivated plants and e.g. grow naturally in wild populations. “Wild lettuce” or “wild Lactuca” accessions refers to plants of species other than cultivated Lactuca sativa, such as Lactuca virosa, Lactuca serriola, Lactuca saligna, Lactuca perennis, and others.Preferably, such wild lettuce comprises or consists of Lactuca species which are cross fertile withL. sativa, optionally with the aid of embryo rescue techniques (see Maisonneuve 1987, Agronomique 7: 313-319 and Maisonneuve et al. 1995, Euphytica 85:281-285) and / or chromosome doubling techniques (Thompson and Ryder 1961, US Dept Agric Tech Bul.1224),or methods whereby genes can be transferred into L. sativa via a bridge species, such as L.serriola (Eenink et al. 1982, Euphytica 31, 291–299, / / doi.org / 10.1007 / BF00021643).The term "food" is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins,Nunhems Netherlands B.V. 240134WO0127 vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism's cells in an effort to produce energy, maintain life, or stimulate growth. The term foodincludes both substances consumed to provide nutritional support for the human and animal body.“Harvested plant material” refers herein to plant parts (e.g., leaves, leaf parts or heads detached from the whole plant) which have been collected for further storage and / or further use. “Harvested seeds” refers to seeds harvested from a line or variety, e.g., produced after self- fertilization or cross-fertilization and collected. “Harvested leaves” or “harvested heads” as used herein refers to lettuce leaves, or leaf parts or heads, i.e., the plant without the root system, for example substantially all (harvested) leaves. Leaves may be whole or cut into parts. "Vegetative propagation" or "clonal propagation" refers to propagation of plants from vegetativetissue, e.g. by propagating plants from cuttings or by in vitro propagation. In vitro propagationinvolves in vitro cell or tissue culture and regeneration of a whole plant from the in vitro culture.Clones (i.e. genetically identical vegetative propagations) of the original plant can thus begenerated by in vitro culture. "Cell culture" or "tissue culture" refers to the in vitro culture of cellsor tissues of a plant. "Regeneration" refers to the development of a plant from cell culture or tissueculture or vegetative propagation. “Non-propagating cell” refers to a cell which cannot be regenerated into a whole plant. “Somatic cells” and “reproductive cells” can be distinguished, whereby somatic cells are cells other than gametes (e.g. ovules and pollen), germ cells and gametocytes. Gametes, germ cells and gametocytes are “reproductive cells”.“Tissue Culture” or “cell culture” refers to an in vitro composition comprising isolated cells of thesame or a different type or a collection of such cells organized into plant tissue. Tissue cultures and cell cultures of lettuce, and regeneration of lettuce plants therefrom, is well known and widely published (see, e.g., Teng et al., HortScience.1992, 27(9): 1030-1032 Teng et al., HortScience. 1993, 28(6): 669-1671, Zhang et al., Journal of Genetics and Breeding.1992, 46(3): 287-290). A “plant line” or “breeding line” refers to a plant and its progeny being highly uniform in plant phenotype. As used herein, the term "inbred line" refers to a plant line which has been repeatedly selfed and is nearly homozygous for all alleles. Thus, an “inbred line” or “parent line” refers to a plant which has undergone several generations (e.g. at least 3, 4, 5, 6, 7 or more) of inbreeding, resulting in a plant line with a high uniformity. The terms "F1, F2, etc." refer to the consecutive related generations following a cross between two parent plants or parent lines. The plants grown from the seeds produced by crossing two plants or lines is called the F1 generation. Selfing the F1 plants results in the F2 generation, etc. The term "hybrid" plant (or hybrid seed) refers to a plant or seed obtained from crossing two inbred parent lines. The term "F1 hybrid" plant (or "F1 hybrid" seed or "F1 seed") refers to a first- generation plant or seed obtained from crossing two inbred parent lines. “Hybrid” refers to the seeds harvested from crossing one plant line or variety with another plant line or variety, and the plants or plant parts grown from said seeds.Nunhems Netherlands B.V. 240134WO0128 “F1 hybrid” plant (or F1 hybrid seed) is the generation obtained from crossing two non-isogenic inbred parent lines. Thus, F1 hybrid seeds are seeds from which F1 hybrid plants grow. An “interspecific hybrid” refers to a hybrid produced from crossing a plant of one species, e.g. L. sativa, with a plant of another species, e.g. L. virosa. The terms "progeny", "progenies" and "descendants", as used herein, refer to any and all offspringthat are derivable from or obtainable from a plant that comprises at least one copy of a mutantPhyB allele as described herein and comprises the delayed bolting phenotype and / or shadetolerance phenotype as described herein when the mutant PhyB allele is in homozygous form.Progeny are derived by crossing a plant comprising at least one copy of a mutant PhyB-allele with another lettuce plant and / or selfing a plant comprising at least one copy of a mutant PhyB- allele one or more times, e.g.2, 3, 4, 5 or more times. Progeny may also be derived by cell culture or by tissue culture, or by producing seeds of a plant. The term progeny may also encompass plants derived from crossing of at least one parent plant with another plant of the same or anothervariety or (breeding) line. A progeny is directly derived from, obtained from, obtainable from orderivable from the parent plant by, e.g., traditional breeding methods (selfing and / or crossing) or regeneration or transformation. However, the term "progeny" generally encompasses further generations such as second, third, fourth, fifth, sixth, seventh or more generations, i.e., generations of plants which are derived from, obtained from, obtainable from or derivable from the former generation by, e.g., traditional breeding methods, regeneration or genetic transformation techniques. For example, a second-generation progeny can be produced from afirst generation progeny by any of the methods mentioned above. A progeny plant may also be adouble haploid plant comprising two copies a mutant LsphyB-allele as described.As used herein, a plant (or plant line or variety or genotype) having a "delayed bolting" relates toa plant (or plant line or variety or genotype, e.g. 5,10,15 or more plants) showing a phenotypewherein the average start of bolting of the plant is delayed by at least 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20 or more days when compared to the average start of bolting of a suitablecontrol plant (or plant line or variety) grown under the same conditions, e.g. in the open field or inglasshouses. The average start of bolting can e.g. be measured by sowing a plurality of seeds ofthe plant line or genotype and the control line or genotype and e.g. cutting heads transversely ate.g. weekly intervals and inspecting whether the transition from vegetative to reproductive stage has started (as seen by elongation of the shoot apical meristem, see Examples). The average number of days after sowing until the start of bolting is then compared between the plant line or genotype comprising a mutant LsPhyB-allele in homozygous form and the wild type control linecomprising the wild type LsPhyB -allele in homozygous form.For lettuce plant growth and development, a number of consecutive development stages can bediscerned by visual inspection of the plants. After germination of the lettuce seed the plant entersthe “seedling stage” in which the roots and the seed cotyledons are formed. Typically, the seedlingstage lasts e.g.14-60 days, considering different lettuce types and seasons. Following theseedling stage, the lettuce plant enters the “vegetative growth stage” in which the lettuce head isdeveloped, and which starts when the third true leaf is fully developed. Typically, the vegetativegrowth stage lasts e.g.60-120 days, considering different lettuce types and seasons. In lettucecultivation for food production, the harvested plant material (i.e. leaves or heads) is collectedwhen the lettuce plant is in the vegetative growth stage, preferably during the second half of thevegetative growth stage. Following the vegetative growth stage, the lettuce plant enters theNunhems Netherlands B.V. 240134WO0129“bolting stage” which starts when a visibly recognisable stalk has started to develop in the centreof the lettuce head. Prior to bolting, the lettuce head shows a typical compact filling of the leaves,which is also described herein as an “intact shape of the (lettuce) head”. Accordingly, a lettuce head of a plant that is harvested from a lettuce plant that is not yet in bolting stage shows compact filling of the leaves and accordingly an intact shape of the lettuce head. Following the bolting stage, the lettuce plant enters the “mature reproductive stage” which starts when the first plant reproductive organs become functional. In general, it is understood that comparisons between different plants or plant lines or varieties involves growing a number of plants of a line (or variety) (e.g. at least 5 plants, preferably at least 10 plants per line) under the same conditions as the plants of one or more control plant lines (preferably wild type plants, e.g. isogenic lines or genetic controls) and the determination of differences, preferably statistically significant differences, between the plant lines when grown under the same environmental conditions. Preferably the plants to be compared and the controlsare of the same or similar genetic background. The control plants may for example be isogenicor near isogenic to the plants to which they are compared. The term "isogenic” plant genotyperefers to two plant genotypes which are genetically identical except for the gene of which theeffect on the phenotype is to be compared, e.g. the difference in phenotype between a plant genotype comprising the wild type LsPhyB allele in homozygous form and a plant comprising a mutant LsPhyB-allele in homozygous form. Similarly ‘near isogenic lines’ are genetically almostidentical in their genetic background, except for the genotype of the PhyB allele."Induced mutant alleles” are mutant alleles in which the mutation(s) is / are / have been induced by human intervention, e.g. by mutagenesis via physical or chemical mutagenesis methods or via e.g. tissue culture (as described in e.g. Zhang D, et al. (2014) Tissue Culture-Induced Heritable Genomic Variation in Rice, and Their Phenotypic Implications. PLOS ONE 9(5): e96879), including also targeted gene editing techniques (such as Crispr based techniques, base editing, prime editing, TALENS, etc.).“SNP marker” refers to a ‘Single Nucleotide Polymorphism’ between e.g. a mutant PhyB-allele,and a wild type PhyB-allele. Using a SNP marker assay, or a SNP genotyping assay, which candistinguish between the mutant and wild type allele of the gene (i.e. an allele specific assay) one can screen pants, plant parts or the DNA therefrom for the presence of the mutant allele and / orthe wild type allele, i.e. for their genotype at the PhyB locus. For example, the SNP underlyingthe Q750* codon change is a SNP marker that can distinguish between the wild type or mutantallele. A SNP genotyping assay is provided herein for this SNP, but alternative assays can, offcourse, be designed and used. For any mutation in the genomic DNA of a mutant PhyB-alleleencoding a mutant protein, a SNP assay can easily be designed.“INDEL marker” refers to an insertion / deletion polymorphism between e.g. a mutant PhyB - alleleand a wild type PhyB - allele. Using an INDEL marker assay, or a genotyping assay, which candistinguish between the mutant and wild type allele of the gene (i.e. an allele specific assay) one can screen plants, plant parts or the DNA therefrom for the presence of the mutant allele. “Genotyping” methods or assays are methods whereby the genotype or allelic composition of a plant or plant part or seed can be determined. Bi-allelic genotyping assays, such as KASP-assays, can distinguish between two alleles at a locus, e.g. a wild type PhyB-allele and a mutant PhyB- allele.Nunhems Netherlands B.V. 240134WO0130 “Marker assisted selection” or “MAS” is a process of using the presence of molecular markers (such as SNP markers or INDEL markers), which are genetically and physically linked to a particular locus or to a particular chromosome region or allele specific markers, to select plants for the presence of the specific locus or region or allele. For example, a molecular markergenetically and physically linked to the mutant PhyB - allele or an allele specific marker, can beused to detect and / or select e.g. lettuce plants, or plant parts, comprising the mutant PhyB -allele.Allele specific markers are preferred markers, as they select for the allele directly. “Targeted gene editing” is referred to techniques whereby endogenous target genes can be modified, e.g. one or more nucleotides can be inserted, replaced and / or deleted e.g. in the promoter or transcribed region or coding sequence. For example CRISPR based techniques,such as Crispr-Cas9 gene editing, Crispr-CpfI gene editing, Crispr – Cas12 (or a subtype ofCas12, such as Cas12a) gene editing or more recent techniques called ‘base editing’ or ‘primeediting’ (see review Molla et al.2021, Nature Plants, VOL 7, p 1166–1187) can be used to modifyendogenous target genes, such as the endogenous wild type PhyB gene in lettuce (encoding theprotein of SEQ ID NO: 1 or a wild type protein comprising at least 95% sequence identity to SEQID NO: 1). The mutants described herein can, for example, be reproduced by targeted geneediting of the wild type PhyB gene.“Oligonucleotides” or “oligos” or “oligonucleotide primers or probes” are short, single-stranded polymers of nucleic acid, e.g. at least 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or more nucleotides in length. Oligos may be unmodified or modified with a variety of chemistries depending on their intended use, for example, the addition of 5' or 3' phosphate groups to enableligation or block extension, respectively, labelling with radionucleotides or fluorophores and / orquenchers for use as probes, the incorporation of thiol, amino, or other reactive moieties to enable the covalent coupling of functional molecules such as enzymes, and extension with other linkers and spacers of diverse functionality. DNA oligos are the most commonly used, but RNA oligos are also available. The length of an oligo is usually designated by adding the suffix -mer. For example, an oligonucleotide with 19 nucleotides (bases) is called a 19-mer. For most uses, oligonucleotides are designed to base-pair with a strand of DNA or RNA. The most common use for oligonucleotides is as primers for PCR (polymerase chain reaction). Primers are designed with at least part of their sequence complementary to the sequence targeted for amplification. Optimal primer length for a complementary sequence is e.g. 18 to 22 nucleotides. Optimal primer sequences for PCR are usually determined by primer design software. “DNA microarrays” are arrays which have many microscopic spots of DNA, usually oligonucleotides, bound on a solid support. Assay targets can be DNA, cDNA, or cRNA. Depending on the system, the hybridization of targets to specific spots is detected by fluorescence, chemiluminescence, or colloidal silver or gold. Microarrays are used for multiple applications such as simultaneous measurement of the expression of large numbers of genes, enabling genome-wide gene expression analysis, as well as genotyping studies using e.g. single- nucleotide polymorphism (SNP) or InDel analysis. “Complementary strands” refer to two strands of complementary sequence, and may be referred to as sense (or plus) and anti-sense (or minus) strands for double stranded DNA. The sense / plus strand is, generally, the transcribed sequence of DNA (or the mRNA that was generated intranscription), while the anti-sense / minus strand is the strand that is complementary to the senseNunhems Netherlands B.V. 240134WO0131 sequence. For any of the sequences provided herein only one strand of the sequence is given, but the complementary strand of the given strand is also encompassed herein. The complementary nucleotides of DNA are A complementary to T, and G complementary to C. The complementary nucleotides of RNA are A complementary to U, and G complementary to C.Plants encompassed hereinThe inventors generated a mutant lettuce population and screened the population in the field for mutant plants which showed a delay in the start of bolting by at least 7 days, especially by at leastby 14 days compared to the wild type control. They then generated two F2 populations from aselected mutant plant which showed a delay in the start of bolting by crossing the mutant plant with a wild type lettuce variety and mapped the QTL responsible for the delay in the start of bolting to a region on chromosome 1. After fine mapping, they surprisingly found that in the QTL region the allele of the Phytochrome B gene contained a mutation (single nucleotide replacement) in the codon which coded for amino acid 750. This codon had changed into a premature translation STOP codon in the mutant plant, causing the PhyB protein to be truncated. Further analysis confirmed that this Q750STOP mutant allele of the Phytochrome B gene was responsible for the delay in the start of bolting by at least 7 days, especially by at least 14 days. As the mutant did not respond to stress conditions by shade avoidance (e.g. increasing internode length), which iscommonly seen in knockouts of the PhyB gene in other plant species, they were confident to haveidentified the causal gene underlying the delayed bolting phenotype. This was however very surprising, as knockouts of the PhyB gene in other plant species caused earlier bolting and not later bolting as seen herein in lettuce. Apart from the delay by at least about 14 days under field conditions to initiate bolting, the plant developed normal flowers and had normal seed set. The Q750STOP mutation was in the Modulator loop domain of the PhyB protein whereby about half of the Modulator Loop domain was missing and further the PAS2-domain, the HKRD domain and the HATPase Phy-like domain were missing, see Figure 3. Both the Modulator loop domain and the PAS2-domain are needed for dimerization of the PhyB protein and the other domains that were missing are needed for downstream processed. As only the N-terminal region of the protein is fully intact and the C-terminal region is missing almost in its entirety, and as a similar mutanthad recently been described in cucumber, it appeared highly likely that the Q750STOP mutantprotein is non-functional in vivo, i.e. it is a loss-of-function mutant. This was further confirmed byaddition STOP codon mutants in codons preceding the Q750STOP mutation which likewise resulted in a delayed bolting phenotype, see Examples. In one aspect therefore, the inventors found that loss-of-function of the Phytochrome B gene in lettuce (in homozygous form) results in a delay in bolting of the lettuce plant by at least 7 days,especially at least 14 days, compared to the lettuce plant comprising the wild type PhyB gene inhomozygous form. The delay in the start of bolting is most easily seen when the mutant LsPhyB allele (the loss-of-function allele) is introduced into a lettuce type which has an early bolting phenotype with the wild type LsPhyB gene being present. In lettuce types which already have a medium-late bolting phenotype in the presence of the wild type LsPhyB gene, the delay in the start of bolting may be less apparent when the mutant LsPhyB allele is introduced into such a type and the delay may only be a delay in the start of bolting by at least e.g. 3, 4 or 5 days. Therefore, in one aspect the delay in bolting of the lettuce plant comprising the mutant allele inNunhems Netherlands B.V. 240134WO0132 homowzygous form may be at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 days compared to the control. In one aspect the mutant LsPhyB allele, especially a loss-of-function allele, is introduced into a lettuce plant which (in the presence of the wild type LsPhyB allele) has an early bolting phenotype, e.g. starts to bolt at around 30, 31, 35, 40, 45, 46, 47, 48, 49 or 50 days after sowing. Further analysis of the mutant and the wild type lettuce plants showed that the mutant lettuceplant differed in its response to light stress conditions and to high plant density stress conditions.While the wild type lettuce plants showed symptoms of shade avoidance under these stress conditions, especially extended internodes and increased plant height, the homozygous mutant plant did not show these shade avoidance symptoms. Internodes were not extended in the mutant plant and plants were also not taller under these conditions.Therefore, provided herein in one aspect is a Lactuca sativa plant comprising in its genome atleast one copy of a mutant allele of the Phytochrome B (PhyB) gene, wherein the wild type PhyBgene encodes a protein of SEQ ID NO: 1, or a protein comprising at least 95%, 96%, 97%, 98%or 99% amino acid sequence identity to SEQ ID NO: 1, and wherein the mutant allele compriseseither a) a mutation in the promoter region, whereby the mutant allele is not expressed orexpression is reduced compared to the wild type allele or b) a mutation in the transcribed regionor coding region of the allele resulting in a mutant PhyB protein being produced, whereby the mutant PhyB protein comprises one or more amino acids inserted, replaced and / or deleted compared to the wild type protein and wherein the presence of the mutant allele under a) or under b) in homozygous form in said plant results in delayed bolting compared to the wild type plantcomprising the wild type PhyB gene and / or wherein the presence of the mutant allele under a) orb) in homozygous form in said plant results in shade tolerance of said plant.In one aspect the mutant protein is a loss-of-function mutant protein or a reduce-function protein.In one aspect the mutant protein comprises a deletion, replacement and / or insertion of one or more amino acids compared to the wild type protein, whereby the deletion, replacement and / orinsertion results in a loss-of-function of the protein in vivo and to delayed bolting when the mutantallele is in homozygous form. Any deletion, replacement and / or insertion of one or more amino acids can lead to a loss of function and the skilled person can easily determine which mutant alleles encode a loss-of-function protein. Especially any premature stop codon, which results in a truncation of the wild type protein by at least 100, 125, 130, 135, 136 or more C-terminal amino acids will lead to a loss of function as thereby at least one of the conserved domains is lackingfrom the protein. A premature stop codon may thus be in an amino acid of one of the conserveddomains or in an amino acid preceding any of the conserved domains to result in a loss-of-function protein. In one aspect the mutant protein comprises a deletion, replacement and / or insertion of one or more amino acids in the PAS1 domain, and / or in the Modulator Loop domain and / or the PAS2 domain, and / or in the HKRD domain and / or in the HATPase Phy-like domain. In one aspect the mutant protein is truncated and lacks all or part of the PAS1 domain, and / or ofthe Modulator Loop domain and / or the PAS2 domain, and / or of the HKRD domain, and / or of theHATPase Phy-like domain. In one aspect the mutant protein is truncated and lacks at least 50, 60, 70, 80, 90, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650 or more of the C-Nunhems Netherlands B.V. 240134WO0133 terminal amino acids compared to the wild type protein. In one aspect the mutant protein is truncated whereby the truncation starts in the Modulator loop domain or preceding the Modulator loop domain, e.g. there is a premature STOP codon mutation in a codon of the Modulator loop domain or of a codon preceding the Modulator loop domain. Non-limiting examples are the STOPcodon mutations described in Example 6 herein.In one aspect, therefore, a Lactuca sativa plant or plant part is provided herein comprising in itsgenome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene, wherein the mutant allele comprises a mutation in the promoter sequence of SEQ ID NO: 7 (or in a promoter comprising at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 7) resulting in decreased gene expression compared to a corresponding wild type allele or no gene expression, or wherein the mutant allele encodes a protein comprising a deletion, truncation, insertion and / or replacement of one or more amino acids compared to the protein encoded by the wild type allele, resulting in e.g. a reduced function or a loss-of-function of the LsPhyB protein, wherein the mutant allele delays the start of bolting of the Lactuca sativaplant by at least 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or 21 or more days when themutant allele is present in homozygous form compared to the control plant lacking the mutantallele, and / or wherein the mutant allele confers shade tolerance, e.g. elongation of the internodesand / or increased plant height under high density stress and / or light stress conditions (e.g. underconditions wherein the wild type plant does show elongation of the internodes and increased plantheight) when the mutant allele is present in homozygous form.When referring herein to the mutant ‘does not’ show elongation of the internodes and / or ‘does not’ show increased plant height, this encompasses in one aspect that the mutant shows some internode elongation and / or increase in plant height, but significantly less than the wild type plant under the same conditions.Herein the LsPhyB protein of the wild type allele is encoded by nucleic acid molecules selectedfrom the group consisting of: a) nucleic acid molecules, which encode a protein with the amino acid sequence given under SEQ ID NO: 1; b) nucleic acid molecules, which encode a protein, the sequence of which has an identity of at least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQID NO: 1; c) nucleic acid molecules, which comprise the nucleotide sequence shown under SEQ ID NO: 5 or a complimentary sequence thereof; d) nucleic acid molecules, which have an identity of at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% with the nucleic acid sequences described under c);e) nucleic acid molecules, which hybridize with at least one strand of the nucleic acid molecules described under a), b), c), or d) under stringent conditions of at least one wash in 0.2X SSC at a temperature of at least 50°C for 20 min; and f) nucleic acid molecules, the nucleotide sequence of which deviates from the sequence of the nucleic acid molecules identified under a) or b) due to the degeneration of the genetic code.Nunhems Netherlands B.V. 240134WO0134 The wild type mRNA (presented as cDNA herein, i.e. Thymine instead of Uracil) is the nucleic acid molecule of SEQ ID NO: 3, or an mRNA (cDNA) of a functional variant comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to the mRNA (cDNA) of SEQ ID NO: 3.As mentioned, in one aspect the mutant allele is not expressed due to a mutant promoter, or themutant allele encodes a loss-of-function protein. Thus, in one aspect (in case of a non functionalpromoter) no mRNA (cDNA) is produced by the allele in the plant and no wild type PhyB proteinis made. In case of a loss-of-function protein being encoded by the mutant allele only non-functional mutant protein is produced by the allele.In another aspect the mutant allele comprises reduced expression due to a mutant promoter, orthe mutant allele encodes a reduced-function protein. Thus, a reduced level of wild type mRNA(cDNA) is produced in the plant due to a mutant promoter (e.g. only 30% or less, 20% or less, 10% or less, 5% or less, 3% or less, 2% or less or 1% or less of the level that is produced by the wild type promoter). In case of a reduced-function protein being encoded by the mutant allele only reduced-functional mutant protein is produced by the allele. For example the mutant proteinmay not be able to form stable dimers.The presence of any of such mutant alleles can in one aspect be seen when the mutant allele is in homozygous form and by e.g. determining if there is a delay in the start of bolting time or by e.g. growing the plants under conditions which lead to shade avoidance symptoms in the wildtype plant. Thus, growing the mutant plant and the wild type plant under high plant densityconditions and / or under a R:FR light ratio of e.g. equal to or less than 0.6, 0.5, 0.4, 0.3, 0.2 or 0.1 and measuring the internode lengths and / or plant height. When the wild type plant (comprising the wild type PhyB allele in homozygous form) shows e.g. internode elongation and / or increasedplant height under these conditions and when the plant homozygous for the mutant PhyB alleledoes not show shade avoidance symptoms, then the mutant allele encodes a loss-of-functionprotein or a reduced-function protein. Likewise, the presence of a mutant allele comprising amutant promoter in homozygous form, resulting in no wild type PhyB protein being made orsignificantly reduced wild type PhyB protein being made leads to the same phenotype. The skilledperson can therefore generate different mutant alleles and test their phenotype regarding shade tolerance and / or start of bolting in order to determine whether the mutant allele has the desired effect and is an allele as provided herein. Any mutant allele encoding a loss-of-function mutant PhyB protein is encompassed herein. Such alleles can be generated by e.g. targeted gene editing or mutagenesis followed by selection ofplants comprising mutant alleles of the PhyB gene. Similarly, any mutant allele encoding areduced-function mutant PhyB protein is encompassed herein, with the proviso that the allele confers the phenotype described (delayed bolting and / or shade tolerance) when in homozygous form. Such alleles can be generated by e.g. targeted gene editing or mutagenesis followed by selection of plants comprising mutant alleles of the PhyB gene. The same applies for mutant alleles comprising no expression or reduced expression in the plant compared to the wild type allele. Various mutant alleles will encode loss-of-function (or reduced function) PhyB proteins. In one aspect the mutant allele encodes a protein which comprises one or more (e.g.2, 3, 4, 5, 6, 7, 8,9, 10 or more) amino acids inserted, deleted and / or replaced by different amino acids comparedNunhems Netherlands B.V. 240134WO0135 to the wild type protein, especially one or more amino acids of the C-terminal region of the protein, especially one or more amino acids in one of the conserved domains of the C-terminal region of the protein selected from the PAS1-domain, the Modulator Loop domain, the PAS2-domain, theHKRD- domain and the HATPase Phy-like domain.In one aspect the deletion of one or more amino acids in one of the conserved domains of the C- terminal region of the protein selected from the PAS1-domain, the Modulator Loop domain, thePAS2-domain, the HKRD- domain and the HATPase Phy-like domain is due to a mutation in thegenomic DNA whereby a codon of the domain is changed into a STOP codon, thereby truncatingthe protein as of the STOP codon. Thus, in one aspect one of the codons for any one of the aminoacids of the PAS1-domain, the Modulator Loop domain, the PAS2-domain, the HKRD- domain orthe HATPase Phy-like domain is replaced by a STOP codon. In another aspect any one of thecodons for any one of the amino acid of the Modulator Loop domain or preceding the Modulator Loop domain is replaced by a STOP codon, e.g. the codon for Q750 or any codon preceding thecodon for Q750 (e.g. any codon for any of the amino acids 1 to 749) is replaced by a STOP codon.In one aspect a Lactuca sativa plant or plant part is provided, wherein said mutant allele encodesa truncated LsPhyB protein whereby at least all or part of the (wild type) Modulator Loop domainor all or part of the (wild type) PAS2 domain is absent or is replaced by different amino acids thanthose of the wild type protein, said Modulator Loop domain being present from amino acid 745 to amino acid 765 of SEQ ID NO: 1 or the equivalent amino acids in a (functional variant) sequencecomprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1 and saidPAS2-domain being present from amino acid 752 to amino acid 874 of SEQ ID NO: 1 or the equivalent amino acids in a (functional variant) sequence comprising at least 95%, 96%, 97%,98% or 99% sequence identity to SEQ ID NO: 1, or wherein at least one or more amino acids areinserted, replaced and / or deleted in said (wild type) Modulator Loop domain or in said (wild type)PAS2-domain. The one or more amino acids being inserted, replaced and / or deleted in either orboth of said domains renders the mutant protein to be a loss-of-function protein or a reduced-function protein in vivo, as can be tested as described elsewhere herein.In one aspect the deletion of one or more amino acids in the Modulator Loop domain or in the PAS2-domain is due to a mutation in the genomic DNA whereby a codon of the domain is changedinto a STOP codon, thereby truncating the protein as of the STOP codon. Thus, in one aspectone of the codons for any one of the amino acids of the Modulator Loop domain or one of the codons for any one of the amino acids of the PAS2-domain is replaced by a STOP codon. In another aspect the deletion of one or more amino acids in the Modulator Loop domain or in the PAS2-domain is due to a mutation in the genomic DNA whereby a codon preceding the Modulator loop domain or preceding the PAS2 domain is changed into a STOP codon, thereby truncatingthe protein as of the STOP codon. Thus, in one aspect one of the codons for any one of the aminoacids preceding the Modulator Loop domain or one of the codons for any one of the amino acids preceding the PAS2-domain is replaced by a STOP codon. Examples are the STOP codon mutants described in Example 6.In another aspect a Lactuca sativa plant is provided, wherein in the mutant allele the codon forGlutamine (Q, Gln) at position 750 of SEQ ID NO: 1, or at the equivalent amino acid in a sequencecomprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1, is replacedby a STOP codon. Similarly, a Lactuca sativa plant is provided, wherein the mutant allele encodesNunhems Netherlands B.V. 240134WO0136a truncated LsPhyB protein which comprises the wild type amino acids of amino acid 1 to 749 ofSEQ ID NO: 1, optionally amino acids 750 to 1125 of SEQ ID NO: 1 are replaced by one or more different amino acids.In a further aspect a Lactuca sativa plant is provided, wherein in the mutant allele the codon forGlutamine (Q, Gln) at position 91 of SEQ ID NO: 1, or at the equivalent amino acid in a sequencecomprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1, is replacedby a STOP codon. Similarly, a Lactuca sativa plant is provided, wherein the mutant allele encodesa truncated LsPhyB protein which comprises the wild type amino acids of amino acid 1 to 90 ofSEQ ID NO: 1, optionally amino acids 91 to 1125 of SEQ ID NO: 1 are replaced by one or more different amino acids.In a further aspect a Lactuca sativa plant is provided, wherein in the mutant allele the codon forTryptophan (W, Trp) at position 369 of SEQ ID NO: 1, or at the equivalent amino acid in asequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1,is replaced by a STOP codon. Similarly, a Lactuca sativa plant is provided, wherein the mutantallele encodes a truncated LsPhyB protein which comprises the wild type amino acids of aminoacid 1 to 368 of SEQ ID NO: 1, optionally amino acids 369 to 1125 of SEQ ID NO: 1 are replaced by one or more different amino acids.In a further aspect a Lactuca sativa plant is provided, wherein in the mutant allele the codon forTryptophan (W, Trp) at position 524 of SEQ ID NO: 1, or at the equivalent amino acid in asequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1,is replaced by a STOP codon. Similarly, a Lactuca sativa plant is provided, wherein the mutantallele encodes a truncated LsPhyB protein which comprises the wild type amino acids of aminoacid 1 to 523 of SEQ ID NO: 1, optionally amino acids 524 to 1125 of SEQ ID NO: 1 are replaced by one or more different amino acids.In another aspect a Lactuca sativa plant is provided, wherein in the mutant allele the codon forGlutamine (Q, Gln) at position 549 of SEQ ID NO: 1, or at the equivalent amino acid in a sequencecomprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1, is replacedby a STOP codon. Similarly, a Lactuca sativa plant is provided, wherein the mutant allele encodesa truncated LsPhyB protein which comprises the wild type amino acids of amino acid 1 to 548 ofSEQ ID NO: 1, optionally amino acids 549 to 1125 of SEQ ID NO: 1 are replaced by one or more different amino acids.In another aspect a Lactuca sativa plant is provided, wherein in the mutant allele the codon forGlutamine (Q, Gln) at position 612 of SEQ ID NO: 1, or at the equivalent amino acid in a sequencecomprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1, is replacedby a STOP codon. Similarly, a Lactuca sativa plant is provided, wherein the mutant allele encodesa truncated LsPhyB protein which comprises the wild type amino acids of amino acid 1 to 611 ofSEQ ID NO: 1, optionally amino acids 612 to 1125 of SEQ ID NO: 1 are replaced by one or more different amino acids.In another aspect a Lactuca sativa plant is provided, wherein in the mutant allele the codon forGlutamic acid (E, Glu) at position 707 of SEQ ID NO: 1, or at the equivalent amino acid in asequence comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1,is replaced by a STOP codon. Similarly, a Lactuca sativa plant is provided, wherein the mutantNunhems Netherlands B.V. 240134WO0137allele encodes a truncated LsPhyB protein which comprises the wild type amino acids of aminoacid 1 to 706 of SEQ ID NO: 1, optionally amino acids 707 to 1125 of SEQ ID NO: 1 are replacedby one or more different amino acids.Provided are herein any of the Lactuca sativa plants and plant parts described above, whereinthe Lactuca sativa plant or plant part is homozygous for the mutant allele of the PhyB gene andas a consequence said L. sativa plant comprises delayed bolting and / or shade tolerance.The Lactuca sativa plant comprising the mutant PhyB allele is preferably a cultivated L. sativaplant and may be an inbred plant, a dihaploid (double haploid) plant or a hybrid plant. The L.sativa plant may be a head lettuce type, a loose-leaf lettuce type or a teen-leaf type or baby leaftype. Teen-leaf types are grown longer and harvested at a longer leaf length than baby leaf types. Herein baby leaf means a leaf length at harvest of about 8 to 10 cm. Herein teen leaf means a leaf length at harvest of about 12 to 15 cm.Further provided is herein a seed from which the Lactuca sativa plant describe herein can begrown. Furthermore, also a plant cell, a tissue or a plant part, e.g. a head, leaf, plurality of leaves, leafparts, etc. of the Lactuca sativa plant described herein or of the seed described herein, comprisingthe mutant PhyB allele, preferably in homozygous form, is provided herein.The mutant allele of the LsPhyB gene may be an “induced mutant allele”, i.e. a mutant allelegenerated by human interventions such as e.g. targeted gene editing or random mutagenesis.Suitable mutagenesis methods comprise chemical mutagenesis (e.g. using EMS or MNU mutagenesis or mutagenesis by generating reactive oxygen species) and radiation mutagenesis (e.g. using UV radiation or ion beam radiation). Such methods are also referred to as randommutagenesis methods, as mutations are induced randomly in the genome. Methods such asTILLING can be used to screen mutagenized seeds or plants for the presence of mutant allelesof the PhyB gene.The mutant allele of the PhyB gene may also be generated by targeted mutagenesis methods,such as targeted gene editing methods including, but not limited to, CRISPR / Cas9 - basedtargeted mutagenesis methods and CRISPR / Cpf1 -based targeted mutagenesis methods. It isnoted that the exact same mutant allele as provided herein or as described herein, e.g. in theExamples, can be generated by the skilled person without undue burden using random or targetedmutagenesis. Selfing of the mutants can then generate plants which are homozygous for the mutant allele and the effect of the homozygous mutant allele on the phenotype (start of bolting and / or shade tolerance) can be tested as described.A mutant LsPhyB allele may also be identified by screening of wild lettuce plants (e.g. landraces,PI accession, CGN accessions, etc.) or by screening orthologs of the Lactuca sativa PhyB genein wild relatives of Lactuca sativa. Such a “natural mutant allele”, which may be identified in a wildplants and / or in wild relatives of Lactuca sativa, may be introgressed into a cultivated Lactucasativa plant using standard breeding methods to provide a plant as encompassed herein. It is inone aspect preferred that the mutant allele is an induced mutant allele and not a ‘natural mutantallele’. The plant provided herein is in one aspect a cultivated (or domesticated) Lactuca sativaNunhems Netherlands B.V. 240134WO0138plant. Introgression of natural mutant alleles from e.g. wild relatives of lettuce has thedisadvantage that generally linkage drag, i.e. the additional transfer of undesired traits, occurs.In one aspect, the mutant allele provided herein delays the average start of bolting of the Lactucasativa plant when present in homozygous form. Preferably, the mutant allele delays average startof bolting of the Lactuca sativa plant when present in homozygous form by at least 7, 8, 9, 10, 11,12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, or more days when compared toa suitable control plant comprising the wild type allele. In one aspect the mutant allele in additionto the delay in bolting phenotype or in the alternative causes the plant to be shade tolerant, e.g.to not show elongation of the internodes and / or increased plant height under growing conditionsor cultivation conditions where shade avoidance symptoms are seen in the control plantscomprising the wild type (non-mutated) LsPhyB allele in homozygous form. In one aspect thecontrol plant comprises a wild type allele of the LsPhyB gene selected from the group consistingof: a) a nucleic acid molecule, which encodes a protein with the amino acid sequence givenunder SEQ ID NO: 1;b) a nucleic acid molecule, which encodes a wild type LsPhyB protein, the amino acidsequence of which has a sequence identity of at least 95%, 96%, 97%, 98% or 99% withthe amino acid sequence given under SEQ ID NO: 1;c) a nucleic acid molecule, which comprises the nucleotide sequence shown under SEQID NO: 5 or a complimentary sequence thereof;d) a nucleic acid molecule, which has a sequence identity of at least 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98% or 99% with the nucleic acid sequence of SEQ ID NO:5; e) a nucleic acid molecule, which hybridize with at least one strand of the nucleic acid molecules described under a), b), c), or d) under stringent conditions of at least one wash in 0.2X SSC at a temperature of at least 50°C for 20 min; and f) a nucleic acid molecule, the nucleotide sequence of which deviates from the sequence of the nucleic acid molecules identified under a) or b) due to the degeneration of the genetic code.The plant provided herein comprises at least one copy of the mutant allele as provided herewith.Such a plant may, thus, be heterozygous for the mutant allele. Such a heterozygous plantcomprises (at least) one copy of the wild type allele and (at least) one copy of the mutant allele.As the gene is recessive, such a heterozygous plant shows a normal bolting phenotype and / orshade avoidance symptoms, i.e. the same phenotype as wild type plants (i.e. plants homozygousfor the wild type PhyB allele). In one aspect also plants and plant parts are provided hereincomprising the mutant LsPhyB allele in heterozygous form. Such heterozygous plants can alsobe advantageously used for breeding to generate offspring that are homozygous for the mutantPhyB allele as further described herein.Nunhems Netherlands B.V. 240134WO0139In one aspect, the Lactuca sativa plant or plant part is homozygous for the mutant allele. Such aplant is inter alia characterized in that it shows an average delayed bolting and / or shade toleranceas further described herein.In a different aspect the Lactuca sativa plant or plant part or seed is homozygous for the mutantallele which results in a mutated reduced-function or loss-of-function LsPhyB protein (e.g. atruncated LsPhyB protein) or wherein the mutant allele comprises a mutant promoter whichresults in reduced expression or no expression of the gene and the plant is inter alia characterizedin that it shows an average delayed bolting and / or shade tolerance, as further described herein.In one aspect the plant is homozygous for the mutant allele and can flower normally, especiallyto be able to generate progeny seeds from the plant, which seeds comprise the mutant allele inhomozygous form. Seeds from which a plant as provided herein can be grown and seedsproduced on a plant as provided herein, e.g. after self pollination, are encompassed herein. The seeds may comprise the mutant allele in homozygous or heterozygous from. Also parts of such seeds are encompassed, such as seed coat, embryo, etc.As mentioned, the Lactuca sativa plant or plant part or seed comprising one or two copies of themutant LsPhyB-allele may be an inbred plant, a dihaploid (or double haploid) plant or a hybridplant. As lettuce is a self-pollinating crop, it is preferably an inbred plant line or variety comprisingone or two copies of the mutant LsPhyB-allele. In one aspect, accordingly, the plant providedherein is an inbred plant. Such an inbred plant is highly homozygous, for instance by repeatedselfing or self pollination steps. In one aspect, the disclosure provides for haploid plants and / or dihaploid (double haploid) plants, which comprise the mutant LsPhyB allele as described herein. Haploid and dihaploid plants can for example be produced by anther or microspore culture and regeneration into a whole plant. For dihaploid production chromosome doubling may be induced using known methods, such as colchicine treatment or the like. So, in one aspect a Lactuca sativaplant is provided, comprising a delayed bolting phenotype and / or shade tolerance as described,wherein the plant is a dihaploid plant. Likewise plant parts of a haploid or dihaploid plant are encompassed as are seeds from which such a plant grows or produced by such a plant.The plants provided herein may be used to produce food or feed. Provided is, thus, the use of aplant or seed of the species Lactuca sativa as disclosed herein as a crop for consumption or togrow a crop. Particularly the harvested leaves and / or harvested heads produced by the plantscan be advantageously used as a crop for consumption.The Lactuca sativa plant or seed may be of any type, such as heading and non-heading types oflettuce. It may be of any horticultural type, such as e.g. (loose) leaf type, butterhead type,Crisphead type or a Romaine / cos type, or even intermediate types. The major horticultural typesof lettuce are e.g. described in Park et al. 2021 (supra). In one aspect, the Lactuca sativa plant orseed is of the head lettuce type or of the teen leaf type, loose leaf type or baby leaf type. In oneaspect, the Lactuca sativa plant or seed is a butterhead type. In one aspect the lettuce is of abutterhead type or a loose leaf type, such as a multi-leaf type. In one aspect the lettuce plant isnot Crisphead type, such as a Batavia lettuce type. In a further aspect the lettuce is not a stem lettuce type. As the lettuce plant which comprises the mutant allele in homozygous form comprises delayed bolting and / or shade tolerance it is in one aspect grown under environmental conditions whichinduce or can induce Shade Avoidance in the control plant, e.g. in the wild type control, wherebyNunhems Netherlands B.V. 240134WO0140the yield and / or quality of the mutant lettuce leaves or lettuce heads is significantly higher than inthe wild type grown under the same conditions. The mutant plants may, therefore, advantageouslybe grown at seedling / plant densities of equal to or above 200 plants per square meter, e.g. equal to or above 250 plants per square meter, equal to or above 300 plants per square meter, equal to or above 350 plants per square meter or equal to or above 400 plants per square meter.Alternatively or in addition to the increased plant densities described above the mutant plants mayadvantageously be grown under far red light supplementation or under controlled environment or natural environment conditions (e.g. winter periods) where the ratio of R:FR is equal to or below 0.6, 0.5, 0.4, 0.3, 0.2 or 0.1. In one aspect the mutant plants are loose leaf types, teen-leaf types or baby leaf types and are gown in hydroponic culture, preferably with automation from seeding to harvest, e.g. in hydroponic trays where the leaves are machine harvested at harvest stage. Hydroponic culture systems are known in the art.The plants provided herein may be used to produce propagation material. Such propagationmaterial comprises propagation material suitable for and / or resulting from sexual reproduction, such as pollen and seeds. Such propagation material comprises propagation material suitable for and / or resulting from asexual or vegetative reproduction including, but not limited to cuttings,grafts, tubers, cell culture and tissue culture. In one aspect, thus, the use of a Lactuca sativa plantas a source of propagation material is provided herein.In one aspect also seed from which the Lactuca sativa plant comprising one or preferably twocopies of the mutant LsPhyB allele can be grown is provided herein. Furthermore, a plurality ofsuch seed is encompassed herein. Such a seed can be distinguished from other seeds due tothe presence of the mutant allele of the LsPhyB gene as described herein, either phenotypically(based on plants having the delayed bolting phenotype and / or shade tolerance) and / or usingmolecular methods to detect the mutant allele in the cells or tissues, such as molecular genotyping methods to detect the mutant allele or sequencing. Also provided is a method of genotyping the DNA of plants or of seeds or plant parts for the presence of a mutant allele of the LsPhyB-gene and optionally selection of a plant or seed or plant part or a plurality plants or seeds or plant parts for a particular genotype, e.g. homozygous for the mutant LsPhyB-allele. In one aspect a KASP-assay may be used for genotyping. However, also other genotyping assays may be used, such as Taqman, etc. In one aspect, a plurality of seed is packaged into a container (e.g. a bag, a carton, a can etc.). Containers may be any size. The seeds may be pelleted prior to packing (to form pills or pellets) and / or treated with various compounds, including seed coatings. In a further aspect a plant part, obtained from (or obtainable from) a lettuce plant comprising oneor preferably two copies of the mutant LsPhyB allele as described is provided herein, and acontainer or a package comprising said plant part. In one aspect a plant cell, tissue or plant partof the Lactuca sativa plant comprising one or preferably two copies of the mutant LsPhyB alleleor of the seed from which the Lactuca sativa plant comprising one or preferably two copies of themutant LsPhyB allele can be grown is provided, wherein said cell, tissue or plant part comprisesthe mutant allele of the LsPhyB gene. In one aspect the plant part is a lettuce head, a leaf, a leafpart or a plurality of leaves comprising in their genome one or two copies of a mutant LsPhyB-Nunhems Netherlands B.V. 240134WO0141allele as described. In one aspect the head, leaf or leaf part is harvested and optionally packagedin bags, cartons or the like. In another aspect it is still connected to the roots, e.g. the plants may be in trays or pots. In a further aspect, the plant part is a plant cell. In still a further aspect, the plant part is a non- regenerable cell or a regenerable cell. In one aspect the plant cell is a non-propagating cell. Inanother aspect the plant cell is a somatic cell. The cell comprises one or two copies of a mutantLsPhyB allele as described herein.A non-regenerable cell or a non-propagating cell is a cell which cannot be regenerated into awhole plant through in vitro culture.In a further aspect the plant cell is a reproductive cell, such as an ovule or a cell which is part of a pollen. In an aspect, the pollen cell is the vegetative (non-reproductive) cell, or the sperm cell (Tiezzi, Electron Microsc. Review, 1991). Such a reproductive cell is haploid. When it is regenerated into whole a plant, it comprises the haploid genome of the starting plant. If chromosome doubling occurs (e.g. through chemical treatment), a double haploid plant can beregenerated. In one aspect the plant which comprises the mutant allele of the LsPhyB gene asdescribed herein is a haploid or a double haploid Lactuca sativa plant.Moreover, there is provided an in vitro cell culture or tissue culture of the Lactuca sativa plant inwhich the cell- or tissue culture is derived from a plant part described herein, such as, for exampleand without limitation, a leaf, a pollen, an embryo, cotyledon, hypocotyls, callus, a root, a root tip, an anther, a flower, a seed or a stem, or a part of any of them, or a meristematic cell, a somatic cell, or a reproductive cell.Further provided is a vegetatively propagated plant, wherein said plant is propagated from a plantpart comprising at least one mutant LsPhyB allele as described herein, preferably two mutant alleles (homozygous).Further, isolated cells, in vitro cell cultures and tissue cultures, protoplast cultures, plant parts,harvested material (e.g. harvested plant material), pollen, ovaries, flowers, seeds, stamen, flowerparts, etc. comprising in each cell at least one copy of the the mutant allele of the LsPhyB geneas described herein are provided. Thus, when said cells or tissues are regenerated or grown intoa whole Lactuca sativa plant, the plant comprises the mutant allele of the LsPhyB gene asdescribed herein, capable of conferring the delayed bolting phenotype and / or shade tolerancephenotype when the allele is in homozygous form.Thus, also an in vitro cell culture and / or tissue culture of cells or tissues is provided. The cell ortissue culture can be treated with shooting and / or rooting media to regenerate a Lactuca sativa plant.Further also, vegetative or clonal propagation of plants comprising at least one, preferably twomutant LsPhyB alleles as described are encompassed herein. Many different vegetativepropagation techniques exist. Cuttings (nodes, shoot tips, stems, etc.) can for example be usedfor in vitro culture as described above. Also, other vegetative propagation techniques exist andcan be used, such as grafting, or air layering. In air layering a piece of stem is allowed to develop roots while it is still attached to the parent plant and once enough roots have developed the clonal plant is separated from the parent.Nunhems Netherlands B.V. 240134WO0142 Thus, in one aspect a method is provided comprising:(a) obtaining a part of a plant comprising a mutant LsPhyB allele (e.g. cells or tissues, e.g.cuttings),(b) vegetatively propagating said plant part to generate an identical plant from the plant part.Thus, also the use of vegetative plant parts for clonal / vegetative propagation is an aspect encompassed herein. In one aspect a method is provided for vegetatively reproducing a Lactucasativa plant comprising at least one (heterozygous), preferably two (homozygous) mutant allelesof the LsPhyB gene as described herein is provided. Therefore, in one aspect a vegetativelyproduced Lactuca sativa plant comprising at least one (heterozygous), preferably two(homozygous) mutant alleles of the LsPhyB gene, as described herein, is provided.In another aspect a Lactuca sativa plant comprising at least one mutant allele of the LsPhyB gene,as described herein, is propagated by somatic embryogenesis techniques. Also provided is a Lactuca sativa plant regenerated from any of the above-described plant partsor regenerated from the above-described cell or tissue cultures, said regenerated plantcomprising in its genome at least one (heterozygous), preferably two (homozygous) mutantalleles of the LsPhyB gene, all as described herein. This plant can also be referred to as avegetatively propagated plant.Furthermore, a food or feed product comprising or consisting of a plant part described herein. Thefood or feed product may be fresh or processed, e.g., canned, steamed, boiled, fried, blanchedand / or frozen etc. Examples are sandwiches, salads, juices, sauces, plant pastes or other foodproducts comprising a plant or a part of a plant which comprises at least one (heterozygous),preferably two (homozygous) mutant alleles of the LsPhyB gene.Therefore, in one aspect a plant part, obtained from (obtainable from) a plant comprising at leastone (heterozygous), preferably two (homozygous) mutant alleles, and a container or a packagecomprising said plant part is provided herein. Particularly, the part comprises in its genome atleast one copy of the mutant allele of the LsPhyB gene as described herein, preferably whereinthe part is selected from the group consisting of a leaf or leaf part, an anther, a pistil, a stem orstem part, a petiole, a root or root part, an ovule, pollen, a protoplast, tissue, a seed or a seedpart, a flower, a cotyledon, a hypocotyl or hypocotyl part and an embryo or embryo part.Accordingly, a part is provided in one aspect, wherein said plant part is a leaf or leaf part, ananther, a pistil, a stem or stem part, a petiole, a root or root part, an ovule, pollen, a protoplast,tissue, a seed or a seed part, a flower, a cotyledon, a hypocotyl or hypocotyl part and an embryoor embryo part and wherein said part comprises in its genome at least one copy of the mutantallele of the LsPhyB gene as described herein. The part is preferably homozygous for the mutantLsPhyB allele. The various stages of development of aforementioned plant parts are comprised,as are parts thereof (e.g. parts of leaves, seeds, etc.).Particularly, harvested plant material such as harvested leaves or harvested heads produced bya plant comprising at least one copy of a mutant LsPhyB allele, as described, is provided. Plantsmay be homozygous or heterozygous for the mutant LsPhyB - allele as described herein.Preferably, the harvested plant material is homozygous for the mutant LsPhyB allele. Theharvested plant material produced by the plant can be distinguished from the harvested plant material according to the prior art by the presence of the mutant allele. In one aspect the harvestedNunhems Netherlands B.V. 240134WO0143material has an improved (average) quality and / or and increased yield of the harvested lettuceheads and / or harvested lettuce leaves compared to the control of the same age and grown underthe same conditions, especially under light stress conditions (a low R:FR ratio) or high densitygrowing (e.g. at least 200 plants per square meter) conditions. Yield is herein referred to as overallyield of a plurality of plants per area, not individual plant yield.Also provided is a method for producing harvested plant material having an improved averagequality (e.g. no elongated internodes and no increased plant height) and / or increased yield, saidmethod comprising growing a Lactuca sativa plant comprising two copies of a mutant LsPhyBallele, as described elsewhere herein, under conditions under which the wild type plant showsshade avoidance symptoms such as elongated internodes and / or increased plant height andharvesting plant material produced by said Lactuca sativa plant.Accordingly, in one aspect a method is provided for producing harvested plant material having ashade tolerance phenotype when compared to a control plant, e.g. isogenic plants, not comprisingthe mutant LsPhyB allele (but a wild type LsPhyB allele in homozygous form) and grown in thesame way (and being the same age), wherein said method comprises growing a Lactuca sativaplant under conditions under which the control plant, e.g. the wild type plant, shows shadeavoidance symptoms such as elongated internodes and / or increased plant height and optionally harvesting plant material produced by said Lactuca sativa plant. In one aspect the plants grown are baby leaf or teen leaf types, comprising two copies of themutant LsPhyB allele and having shade tolerance. In one aspect the growing conditions are ahydroponic system which in the wild type control results in shade avoidance symptoms of the wildtype plant. In one aspect the plants are grown under densities of 200 plants per square meter ormore (250, 300, 350, 400, 450 plants per square meter or more) and / or under light conditions wherein the R:FR ratio is equal to or below 0.6, 0.5, 0.4, 0.3, 0.2, 0.1.In one aspect a method for producing harvested plant material is provided, said methodcomprising growing a Lactuca sativa plant comprising two copies of a mutant LsPhyB allele(homozygous), as described, and harvesting plant material produced by said Lactuca sativa at astage where the wild type plant already starts to bolt, while the mutant plant has not yet startedbolting. The plant producing harvested plant material having a delayed bolting phenotype ishomozygous for the mutant LsPhyB allele as described herein. The harvesting may be done at astage when the control plants are already bolting, i.e. at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 or more days after the control plant (homozygous for the wild type LsPhyB-allele) would start or starts to bolt. The control plant is preferably the same type of lettuce and preferably genetically very similar to the lettuce plant comprising the mutant LsPhyB allele, except that it comprises the wild type LsPhyB allele in homozygous form. The control plantmay, for example, be the wild type lettuce plant originally used to generate the LsPhyB mutantallele by mutagenesis.In one aspect a method of growing a lettuce plant comprising a mutant LsPhyB-allele inhomozygous form is provided, said method comprises sowing seeds of the lettuce plant and harvesting the leaves or heads, optionally harvesting at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 or more days after the control plant (homozygous for the wild type LsPhyB-allele) would start or starts to bolt. Growing may be done in the open field or in a controlled environment or in tunnels.Nunhems Netherlands B.V. 240134WO0144 In one aspect plants, seeds, plant parts and cells as described herein are obtained by a technical method as described herein. In one aspect plants, plant parts and cells are not exclusivelyobtained by means of an essentially biological process, e.g. as defined by Rule 28(2) EPC.Preferably, a process for the production of plants or animals is essentially biological if it consists entirely of natural phenomena such as crossing or selection e.g. as defined by Rule 26(5) EPC.In one aspect the plants, plant parts or seeds do not contain a genetic construct inserted into thegenome through transformation, such as a vector. In one aspect the mutant alleles are generated by random mutagenesis (e.g. chemical or radiation mutagenesis) or by targeted mutagenesis, especially using the CRISPR system (e.g. Crispr / Cas9or Crispr / CpfI or other nucleases). In one aspect the cultivated plant comprising the mutantLsPhyB- allele is not a transgenic plant, i.e. non-transgenic progeny are selected which do notcomprise any vector construct or parts thereof e.g. a CRISPR construct.In one aspect the mutant allele of the LsPhyB gene comprises a human induced mutation, i.e. amutation introduced by random mutagenesis techniques, such as chemical mutagenesis or radiation mutagenesis, or targeted mutagenesis techniques, such as CRISPR-based techniques, base editing or primer editing.A method for targeted mutagenesis of the endogenous LsPhyB gene in lettuce is provided herein,using any targeted gene modification method, such as CRISPR based methods (e.g. Crispr / Cas9 or Crispr / CpfI), base editing, prime editing, TALENS, Zinc Fingers or other methods.Methods of producing or of identifying and / or selecting a plant, seed or plant partFurther provided are methods wherein a Lactuca sativa plant, as described herein, comprising atleast one copy of a mutant allele of the LsPhyB gene, is used and / or obtained.In one aspect, a method for identifying and / or selecting a Lactuca sativa plant or plant part or seed is provided, comprising determining whether said Lactuca sativa plant or plant part or seed comprises in its genome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) geneas described herein, wherein the mutant allele encodes a mutant protein in which one or moreamino acids are inserted, deleted and / or replaced compared to the wild type LsPhyB protein (resulting in reduced function or loss-of-function of the LsPhyB protein as described) or wherein the mutant allele comprises a mutant promoter wherein one or more nucleotides are inserted, deleted and / or replaced compared to the wild type promoter (resulting in reduced expression or no expression as described). The method may comprise steps like -obtaining genomic DNA from the plant or plant part or seed or seed part,- generating a PCR product or a nucleic acid hybridization product for a specific mutantLsPhyB-allele as described herein or generating sequence information of the mutant LsPhyB-allele, -optionally selecting a plant, plant part or seed comprising a specific mutant LsPhyB-allele as described herein and as detected in the previous step.Nunhems Netherlands B.V. 240134WO0145 As mentioned earlier herein the wild type allele is encoded by nucleic acid molecules selected from the group consisting of: a) nucleic acid molecules, which encode a protein with the amino acid sequence given under SEQ ID NO: 1;b) nucleic acid molecules, which encode a protein, the sequence of which has an identity of at least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQ IDNO: 1;c) nucleic acid molecules, which comprise the nucleotide sequence shown under SEQ ID NO: 5 or a complimentary sequence thereof;d) nucleic acid molecules, which have an identity of at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% with the nucleic acid sequences described under c);e) nucleic acid molecules, which hybridize with at least one strand of the nucleic acid molecules described under a), b), c), or d) under stringent conditions of at least one wash in 0.2X SSC at a temperature of at least 50°C for 20 min; and f) nucleic acid molecules, the nucleotide sequence of which deviates from the sequence of the nucleic acid molecules identified under a) or b) due to the degeneration of the genetic code. As mentioned earlier herein the wild type promoter is a nucleic acid molecules selected from the group consisting of: -i) a nucleic acid molecule which comprise the nucleotide sequence shown under SEQID NO: 7; -ii) a nucleic acid molecule which has a sequence identity of at least 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98% or 99% with the nucleic acid sequence shown underSEQ ID NO: 7; -iii) a nucleic acid molecule which hybridizes with at least one strand of the nucleic acidmolecule described under i) or ii) under stringent conditions of at least one wash in 0.2XSSC at a temperature of at least 50°C for 20 min. In one aspect in the method above the mutant allele which encodes a mutant protein in which one or more amino acids are inserted, deleted and / or replaced compared to the wild type LsPhyBprotein (resulting in reduced function or loss-of-function of the LsPhyB protein as described) isselected from a mutant allele as described elsewhere herein, e.g. a mutant allele in which one or more amino acids are inserted, deleted and / or replaced in a conserved domain selected from the group consisting of: the Modulator Loop, the PAS1-domain, the PAS2-domain, the HKRD-domain and the HATPase Phy-like domain. In one aspect the mutant allele comprises a premature STOP codon in one of the conserved domains selected from the group consisting of: the Modulator Loop, the PAS1-domain, the PAS2-domain, the HKRD-domain and the HATPase Phy-like domain or preceding one of these conserved domains, especially preceding the Modulator loop domain,such as the mutants of Example 6 and as described elsewhere herein.Nunhems Netherlands B.V. 240134WO0146In one aspect a method is provided for identifying and / or selecting a Lactuca sativa plant or plantpart or seed comprising in its genome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene, wherein the mutant allele encodes a mutant protein wherein at least all or part of the Modulator Loop domain or all or part of the PAS2-domain is absent, or wherein at least oneor more amino acids are inserted, replaced and / or deleted in (or preceding) the Modulator Loopdomain or in (or preceding) the PAS2-domain, said Modulator Loop domain being present from amino acid 745 to amino acid 765 of SEQ ID NO: 1 or the equivalent amino acids in a sequence comprising at least 95% sequence identity to SEQ ID NO: 1 and said PAS2-domain being present from amino acid 752 to amino acid 874 of SEQ ID NO: 1 or the equivalent amino acids in a sequence comprising at least 95% sequence identity to SEQ ID NO: 1, said method comprisinganalysing whether the genomic DNA of said Lactuca sativa plant or plant part comprises themutant allele.In one aspect the method comprises identifying and / or selecting a Lactuca sativa plant or plantpart or seed comprising in its genome at least one copy of a mutant allele encoding a truncatedprotein selected from the following mutants: Q91STOP, W369STOP, W524STOP, Q549STOP, Q612STOP, E707STOP, Q750STOP, or a mutant allele wherein the wild type amino acid sequence ends at the same amino acid, or at about the same amino acid sequence (e.g. one, two or three amino acids preceding or following the mentioned amino acid) and optionally the truncated wild type sequence may be followed by one or more non-wild type amino acids.In one aspect the method comprises identifying and / or selecting a Lactuca sativa plant or plantpart or seed comprising in its genome at least one copy of a mutant allele wherein a codon in theModulator Loop domain or preceding the Modulator loop domain, or a codon in the PAS2-domain or preceding the PAS2-domain is replaced by a premature STOP codon, whereby the protein is truncated as of the premature STOP codon. In one aspect the mutant allele encodes a truncated LsPhyB protein as described elsewhere herein, e.g. wherein the protein is truncated as of an amino acid in the Modulator loop domain or preceding the Modulator loop domain or where the protein is truncated as of an amino acid in the PAS2-domain or preceding the PAS2-domain, so that the wild type amino acids following the truncation site are missing. Optionally one or more other amino acids may be present than the wild type amino acids, e.g. when a frame shift mutation is present. Examples are e.g. the mutant alleles described in the Examples and further above. The method above may comprise steps like -obtaining genomic DNA from the plant or plant part or seed or seed part,- generating a PCR product or a nucleic acid hybridization product for a specific mutantLsPhyB-allele as described herein or generating sequence information of the mutant LsPhyB-allele, -optionally selecting a plant, plant part or seed comprising a specific mutant LsPhyB-allele as described herein and as detected in the previous step.The presence of any mutant allele described herein can be detected using known methods or anyof the above methods or any methods described throughout the description. In one aspect the mutant allele that is detected is for example the mutant allele which encodes a truncated protein wherein the codon for the Glutamine at amino acid 750 of SEQ ID NO: 1 (aminoNunhems Netherlands B.V. 240134WO0147 acid Q750), or the equivalent amino acid in a wild type LsPhyB protein comprising at least 95% sequence identity to SEQ ID NO: 1, is changed into a stop codon. In another aspect any of the other mutant allele as e.g. described in the Examples is detected,such as a mutant allele encoding a truncated protein selected from the following mutants:Q91STOP, W369STOP, W524STOP, Q549STOP, Q612STOP, E707STOP, Q750STOP, or a mutant allele wherein the wild type amino acid sequence ends at the same amino acid as mentioned for the STOP codon mutants, or at about the same amino acid sequence (e.g. one, two or three amino acids preceding or following the mentioned amino acid), but wherein the truncation is not due to a STOP codon mutation but due to e.g. a frameshift mutation. Optionally the truncated wild type sequence may be followed by one or more non-wild type amino acids. So for example a method for identifying and / or selecting a Lactuca sativa plant or plant part is provided comprising determining whether said Lactuca sativa plant or plant part comprises in itsgenome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene as describedherein, e.g. the mutant allele which encodes a truncated protein wherein the codon for the Glutamine at amino acid 750 of SEQ ID NO: 1 (amino acid Q750), or the equivalent amino acid in a wild type LsPhyB protein comprising at least 95% sequence identity to SEQ ID NO: 1, ischanged into a stop codon or wherein the truncation of the wild type sequence as of amino acid750 is due to another mutation, e.g. an insertion in the genomic DNA, a frame shift, etc.As already described herein, the wild type LsPhyB gene encodes a protein (the LsPhyB protein)comprising at least 95% amino acid sequence identity to SEQ ID NO: 1, e.g 95%, 96%, 97%,98%, 98.3%, 98.7%, 99.0%, or 99.3% or more preferably 99.7% sequence identity to SEQ ID NO: 1 (as determined using methods discloses elsewhere herein, such as pairwise alignment using Needle, default parameters). Preferably, the mutant allele of the LsPhyB gene as comprised in the Lactuca sativa plant or plant part or seed as used in the identification and / or selection method delays bolting and / or causes shade tolerance of the Lactuca sativa plant when the mutant allele is present in homozygous form. The method comprises screening at the DNA, RNA (or cDNA) or protein level using known methods, in order to detect the presence of the mutant allele. There are many methods to detectthe presence of a mutant allele of a gene. For example, if there is a single nucleotide difference(single nucleotide polymorphism, SNP) between the wild type and the mutant allele, a SNPgenotyping assay can be used to detect whether a plant or plant part or cell or seed or seed partcomprises the wild type nucleotide or the mutant nucleotide in its genome. For example, the SNPcan easily be detected using a KASP-assay (see world wide web at kpbioscience.co.uk) or other SNP genotyping assays. For developing a KASP-assay, for example 70 base pairs upstream and 70 base pairs downstream of the SNP can be selected and two allele-specific forward primers and one allelespecific reverse primer can be designed. See e.g. Allen et al. 2011, Plant Biotechnology J. 9,1086-1099, especially p097-1098 for KASP-assay method. Examples are e.g. forward andreverse primers, which are allele specific and can be used in the detection or genotyping of themutant allele, e.g. encoding the Q750* mutation, or any mutant allele described herein. Obviously,various different primers can be designed for detection of the same or different mutations in theNunhems Netherlands B.V. 240134WO0148 genomic DNA. E.g. the primers may be slightly different, e.g. longer or shorter or degenerate with respect of the template DNA. The primers may be designed based on the forward strand or based on the reverse (complementary) strand of the genomic sequence. Equally other genotyping assays can be used. For example, a TaqMan SNP genotyping assay, aHigh Resolution Melting (HRM) assay, SNP- genotyping arrays (e.g. Fluidigm, Illumina, etc.) orDNA sequencing may equally be used. Apart from in-gene markers (like the SNP markers in the LsPhyB-allele provided or described herein), also other molecular markers may be used to aid in the identification of the plants (orplant parts or nucleic acids obtained therefrom) containing a mutant LsPhyB allele. For example,one can develop one or more suitable molecular markers which are closely genetically (and preferably also physically) linked to the mutant LsPhyB allele. This can be done by crossing alettuce plant comprising the mutant allele (preferably capable of producing plants having thedelayed bolting phenotype and / or shade tolerance phenotype) with a lettuce plant comprising thewild type LsPhyB-alleles and having normal bolting and shade avoidance symptoms anddeveloping a segregating population (e.g. F2, F3 or backcross population) from that cross. Thesegregating population can then be phenotyped and genotyped using e.g. molecular markers such as SNPs (Single Nucleotide Polymorphisms), AFLPs (Amplified Fragment Length Polymorphisms; see, e.g., EP 534858), or others, and by software analysis molecular markerswhich co-segregate with the phenotype in the segregating population can be identified and theirorder and genetic distance (centimorgan distance, cM) to the LsPhyB gene (or locus) can beidentified. Molecular markers which are closely linked to LsPhyB locus, e.g. markers at a 5, 3, 2or 1 cM distance or less, can then be used in detecting and / or selecting plants (e.g. plants orprogeny comprising the mutant allele) or plant parts comprising or retaining the fragmentcomprising the mutant LsPhyB allele. Such closely linked molecular markers can replacephenotypic selection (or be used in addition to phenotypic selection) in breeding programs, i.e. in Marker Assisted Selection (MAS). Preferably, linked markers are used in MAS. More preferably, flanking markers are used in MAS, i.e. one marker on either side of the locus of the mutant LsPhyB allele.In one aspect, the method for identifying and / or selecting a Lactuca sativa plant or plant partfurther comprises a step wherein the Lactuca sativa plant or plant part is subjected to a mutationinducing step prior to determining whether the Lactuca sativa plant or plant part comprises amutant allele of the LsPhyB gene.A mutagenizing step may involve the use of ethyl methanesulfonate (EMS) as mutagenic agent.Preferably, the seed, plant or plant part is subjected to a mutation inducing step prior todetermining whether the seed, plant or plant part comprises a mutant allele of the LsPhyB gene.In one aspect ethyl methanesulfonate (EMS) is used as mutagenic agent. Accordingly, said mutation inducing step may comprise contacting said seed, plant or plant partwith a mutagen. Preferably, the seed or plant or plant part that is contacted with the mutagencomprises a wild type LsPhyB allele in homozygous form.Said mutation inducing step may alternatively involve targeted mutagenesis techniques thatdepend on e.g. the site-specific induction of a double strand break in the genomic DNA of a host plant cell. Inducing such a double strand break may comprise contacting a plant or plant part (e.g.Nunhems Netherlands B.V. 240134WO0149 a plant cell) with an engineered nuclease upon which said double strand break may be repaired by the cell’s endogenous DNA double stranded break repair mechanisms (e.g. the homology directed repair mechanism), which allows a site-specific deletion or inversion of DNA in a target cell. Engineered nucleases useful in genome editing methods include meganucleases, zinc finger nucleases (ZFNs), transcription activator-like effector-based nucleases (TALEN), and clustered regularly interspaced short palindromic repeats (CRISPR)-associated nucleases. Genome editing methods particularly useful in the context of the present invention include, but are not limited to, CRISPR / Cas9 -based targeted mutagenesis methods and CRISPR / Cas12 (or a subtype of Cas12 such as Cas12a, also known as CRISPR / Cpf1)-based targeted mutagenesis methods;see e.g. Brooks et al. (2014) Plant Physiol 166, 1292-1297 and WO2016 / 205711 A1.See also e.g. Front. Plant Sci., 02 November 2020, Sec. Plant Biotechnology, Volume 11 – 2020, / / doi.org / 10.3389 / fpls.2020.584151 for Crispr based systems for plant gene editing, especially forusing Crispr-Cas12a as editing system.The mutation-inducing step subsequently causes a mutation in the LsPhyB allele to provide amutant LsPhyB allele that is capable of inducing the delayed bolting trait and / or the shadetolerance phenotype. The specific mutant alleles provided or described herein can be reproducedor generated de novo by any of the above mutagenesis techniques.Also, transgenic plants can be made comprising a construct which reduces or abolishes theexpression of the endogenous (wild type) LsPhyB gene, such as an RNAi construct, as described in further detail herein below.Accordingly provided is a method of producing a Lactuca sativa plant comprising the steps of:(a) obtaining or providing seeds or plant material of a Lactuca sativa plant;(b) treating said seed or plant material with a mutagen to create mutagenized seed or plantmaterial;(c) analyzing said mutagenized seed or plant material to identify a plant having at least onemutation in the LsPhyB gene as defined herein, wherein the wild type LsPhyB gene encodes aprotein of SEQ ID NO: 1 or a protein comprising at least 95% amino acid sequence identity toSEQ ID NO: 1, and wherein the mutant allele is a mutant allele as described anywhere herein,e.g. comprising a mutation in the promoter region, or in the transcribed region or coding region whereby the mutant protein comprises one or more amino acids inserted, deleted and / or replaced compared to the wild type protein.In one aspect a method of producing a Lactuca sativa plant is provided comprising the steps of:(a) obtaining or providing seeds or plant material of a Lactuca sativa plant;(b) treating said seed or plant material with a mutagen to create mutagenized seed or plantmaterial;(c) analyzing said mutagenized seed or plant material to identify a plant having at least onemutation in the LsPhyB gene as defined herein, wherein the wild type LsPhyB gene encodes aprotein of SEQ ID NO: 1 or a protein comprising at least 95% amino acid sequence identity to SEQ ID NO: 1, and wherein the mutant allele either i) encodes a mutant protein comprising a truncation whereby the protein is truncated in or preceding one of the conserved C-terminal domains of the protein selected from the Modulator Loop, the PAS1-domain, the PAS2-domain, the HKRD-domain and the HATPaseNunhems Netherlands B.V. 240134WO0150 Phy-like domain, e.g. in or preceding the Modulator Loop-domain, whereby the remainingamino acids of the C-terminal are missing, in or preceding the PAS1-domain, whereby the remaining amino acids of the C-terminal are missing, or in or preceding the PAS2-domain, whereby the remaining amino acids of the C-terminal are missing, or in or preceding the HKRD-domain whereby the remaining amino acids of the C-terminal are missing, or in or preceding the HATPase Phy-like domain whereby the remaining amino acids of the C-terminal are missing; or ii) encodes a truncated protein, wherein e.g. the final at least 50, 100, 150, 200, 250, 300, 350 C-terminal amino acids are missing;or iii) encodes a mutant protein wherein one or more amino acids of the Modulator Loop domain, the PAS1-domain, the PAS2-domain, the HKRD-domain or the HATPase Phy-like domain are deleted and / or replaced by another amino acid or wherein an amino acid codon in said domain or preceding said domain is mutated into a STOP codon; or iv) encodes a mutant protein wherein one or more amino acids are inserted into theModulator Loop domain, the PAS1-domain, the PAS2-domain, the HKRD-domain or the HATPase Phy-like domain. In one aspect the mutant allele which is truncated still encodes the wild type N-terminal aminoacids 1 to 593 of SEQ ID NO: 1 (or the equivalent amino acids in a variant sequence comprisingat least 95% identity to SEQ ID NO: 1). In another aspect the mutant allele which is truncated still encodes the wild type N-terminal aminoacids 1 to any amino acid prior to amino acid 766 of SEQ ID NO: 1, i.e. any amino acid startingfrom 1 to any amino acid prior to the end of the Modulator loop domain (or the equivalent aminoacids in a variant sequence comprising at least 95% identity to SEQ ID NO: 1), for example, aminoacid 1 to 90, 1 to 368, 1 to 523, 1 to 548, 1 to 611, 1 to 706 or 1 to 749 of SEQ ID NO: 1 (or theequivalent amino acids in a variant sequence comprising at least 95% identity to SEQ ID NO: 1).The truncation of the wild type amino acid sequence may be due to e.g. a stop codon mutation, a frame shift mutation or other mutations, such as an insertion. This embodiment applies both to plants, seeds and plant parts, as well as to methods described herein and whenever reference is made herein to STOP codon mutations it is also encompassed that the truncation of the wild type sequence is not due to a STOP codon mutation but due to a different mutation, such as a frameshift mutations or DNA insertion mutation. Optionally one or more amino acids which are different from the wild type amino acid sequence may follow the N-terminal truncated wild type sequence, as is often the case with frame shiftmutations. It is, therefore, understood that reference herein to a deletion or truncation of one ormore amino acids with respect of the wild type amino acids of the LsPhyB protein includes the possibility that one or more of the deleted or missing wild type amino acids of the wild type LsPhyBNunhems Netherlands B.V. 240134WO0151 protein sequence may be replaced by other amino acids. This occurs for example when a frame shift mutation leads to an out of frame reading. Also TILLING (Targeting Induced Local Lesions IN Genomes) is a general reverse genetics technique that uses traditional chemical mutagenesis methods to create libraries of mutagenized individuals that are later subjected to high throughput screens for the discovery of mutations. TILLING combines chemical mutagenesis with mutation screens of pooled PCR products, resulting in the isolation of missense and non-sense mutant alleles of the targeted genes. Thus, TILLING uses traditional chemical mutagenesis (e.g. EMS or MNU mutagenesis or mutagenesis by generating reactive oxygen species) or other mutagenesis methods (e.g. by radiation mutagenesis using e.g. UV radiation or ion beam radiation) followed by high-throughput screeningfor mutations in specific target genes, such as the LsPhyB gene. S1 nucleases, such as CEL1 orENDO1, are used to cleave heteroduplexes of mutant and wildtype target DNA and detection of cleavage products using e.g. electrophoresis such as a LI-COR gel analyzer system, see e.g.Henikoff et al. Plant Physiology 2004, 135: 630-636. TILLING has been applied in many plantspecies, including Lactuca sativa plants, tomato, rice (Till et al. 2007, BMC Plant Biol 7: 19),Arabidopsis (Till et al. 2006, Methods Mol Biol 323: 127-35), Brassica, maize (Till et al. 2004, BMC Plant Biol 4: 12), etc. Also EcoTILLING, whereby mutants in natural populations are detected, has been widely used, see Till et al. 2006 (Nat Protoc 1: 2465-77) and Comai et al. 2004 (Plant J 37: 778-86). In one embodiment (cDNA or genomic) nucleic acid sequences encoding such mutant LsPhyB protein comprise one or more non-sense and / or missense mutations, e.g. transitions(replacement of purine with another purine (A ↔ G) or pyrimidine with another pyrimidine (C ↔T) or transversions (replacement of purine with pyrimidine, or vice versa (C / T ↔ A / G).In one embodiment a LsPhyB gene nucleotide sequence comprising one or more non-senseand / or missense mutations in one of the exon- encoding sequence are provided, as well as aplant comprising such a mutant allele resulting in a plant capable of producing plants having adelayed bolting phenotype and / or a shade tolerance phenotype when said mutant allele is presentin homozygous form. In one aspect, accordingly, the plant or plant part is identified and / or selected from a TILLINGpopulation that was obtained by subjecting seeds, plants or plant parts to a mutagen as describedin further detail herein below.Thus, in one aspect a method for producing a Lactuca sativa plant is provided comprising thesteps of:(a) providing a TILLING population of a Lactuca sativa plant species,(b) screening said TILLING population for mutants in the LsPhyB gene as described herein,and(c) selecting from the mutant plants of (b) those plants (or progeny of those plants) whichcomprise in their genome at least one copy of a mutant allele of the LsPhyB gene, and whereinthe mutant allele is a mutant allele as described anywhere herein, e.g. comprising a mutation inthe promoter region, or in the coding region or transcribed region, whereby the mutant proteincomprises one or more amino acids inserted, deleted and / or replaced compared to the wild type protein.Nunhems Netherlands B.V. 240134WO0152Therefore, in one aspect a method for producing a Lactuca sativa plant is provided comprisingthe steps of:(a) providing a TILLING population of a Lactuca sativa plant species,(b) screening said TILLING population for mutants in the LsPhyB gene as described herein,and(c) selecting from the mutant plants of (b) those plants (or progeny of those plants) whichcomprise in their genome at least one copy of a mutant allele of the LsPhyB gene, wherein saidmutant allele either i) encodes a mutant protein comprising a truncation whereby the protein is truncated in or preceding one of the conserved C-terminal domains of the protein selected from the Modulator Loop, the PAS1-domain, the PAS2-domain, the HKRD-domain and the HATPase Phy-like domain, i.e. in or preceding the Modulator Loop-domain, whereby the remaining amino acids of the C-terminal are missing, in or preceding the PAS1-domain, whereby the remaining amino acids of the C-terminal are missing, or in or preceding the PAS2-domain, whereby the remaining amino acids of the C-terminal are missing, or in or preceding the HKRD-domain whereby the remaining amino acids of the C-terminal are missing, or in or preceding the HATPase Phy-like domain whereby the remaining amino acids of the C-terminal are missing; or ii) encodes a truncated protein, wherein e.g. the final at least 50, 100, 150, 200, 250, 300, 350 C-terminal amino acids are missing; or iii) encodes a mutant protein wherein one or more amino acids of the Modulator Loop domain, the PAS1-domain, the PAS2-domain, the HKRD-domain or the HATPase Phy-like domain are deleted and / or replaced by another amino acid or wherein an amino acid codon in said domain or preceding said domain is mutated into a STOP codon; or iv) encodes a mutant protein wherein one or more amino acids are inserted into the Modulator Loop domain, the PAS1-domain, the PAS2-domain, the HKRD-domain or the HATPase Phy-like domain.In one aspect the mutant allele in step i) encodes a mutant protein wherein the codon for Q atposition 750 of SEQ ID NO: 1 (or the equivalent codon in a sequence comprising at least 95%sequence identity to SEQ ID NO: 1) is replaced by a different amino acid or by a STOP codon orwherein the mutant protein is truncated as of amino acid 750 of SEQ ID NO: 1 and optionally oneor more non-wild type amino acids are present following amino acid 749 of SEQ ID NO: 1.In another aspect the mutant allele in step i) encodes a mutant protein wherein the codon for Qat position 91 of SEQ ID NO: 1 (or the equivalent codon in a sequence comprising at least 95%sequence identity to SEQ ID NO: 1) is replaced by a different amino acid or by a STOP codon orNunhems Netherlands B.V. 240134WO0153 wherein the mutant protein is truncated as of amino acid 91 of SEQ ID NO: 1 and optionally one or more non-wild type amino acids are present following amino acid 90 of SEQ ID NO: 1.In another aspect the mutant allele in step i) encodes a mutant protein wherein the codon for Wat position 369 of SEQ ID NO: 1 (or the equivalent codon in a sequence comprising at least 95%sequence identity to SEQ ID NO: 1) is replaced by a different amino acid or by a STOP codon orwherein the mutant protein is truncated as of amino acid 369 of SEQ ID NO: 1 and optionally one or more non-wild type amino acids are present following amino acid 368 of SEQ ID NO: 1.In another aspect the mutant allele in step i) encodes a mutant protein wherein the codon for Wat position 524 of SEQ ID NO: 1 (or the equivalent codon in a sequence comprising at least 95%sequence identity to SEQ ID NO: 1) is replaced by a different amino acid or by a STOP codon orwherein the mutant protein is truncated as of amino acid 524 of SEQ ID NO: 1 and optionally one or more non-wild type amino acids are present following amino acid 523 of SEQ ID NO: 1.In another aspect the mutant allele in step i) encodes a mutant protein wherein the codon for Qat position 549 of SEQ ID NO: 1 (or the equivalent codon in a sequence comprising at least 95%sequence identity to SEQ ID NO: 1) is replaced by a different amino acid or by a STOP codon orwherein the mutant protein is truncated as of amino acid 549 of SEQ ID NO: 1 and optionally one or more non-wild type amino acids are present following amino acid 548 of SEQ ID NO: 1.In another aspect the mutant allele in step i) encodes a mutant protein wherein the codon for Qat position 612 of SEQ ID NO: 1 (or the equivalent codon in a sequence comprising at least 95%sequence identity to SEQ ID NO: 1) is replaced by a different amino acid or by a STOP codon orwherein the mutant protein is truncated as of amino acid 612 of SEQ ID NO: 1 and optionally one or more non-wild type amino acids are present following amino acid 611 of SEQ ID NO: 1.In another aspect the mutant allele in step i) encodes a mutant protein wherein the codon for Eat position 707 of SEQ ID NO: 1 (or the equivalent codon in a sequence comprising at least 95%sequence identity to SEQ ID NO: 1) is replaced by a different amino acid or by a STOP codon orwherein the mutant protein is truncated as of amino acid 707 of SEQ ID NO: 1 and optionally one or more non-wild type amino acids are present following amino acid 706 of SEQ ID NO: 1. Mutant plants (M1) are preferably selfed one or more times to generate for example M2 populations or preferably M3 or M4 populations for phenotyping. In M2 populations the mutant allele is present in a ratio of 1 (homozygous for mutant allele) : 2 (heterozygous for mutant allele) : 1 (homozygous for wild type allele).In one aspect a method for producing a Lactuca sativa plant comprising a mutant allele whichdelays bolting of said plant and / or which causes the plant to be shade tolerant when the mutantallele is present in homozygous form is provided, said method comprising the step(s) of:a) crossing a first Lactuca sativa plant and a second Lactuca sativa plant, wherein the firstLactuca sativa plant comprises in its genome at least one copy of a mutant allele of thePhytochrome B (LsPhyB) gene, and wherein the mutant allele is a mutant allele asdescribed anywhere herein, e.g. comprising a mutation in the promoter region, or in the coding region or transcribed region, whereby the mutant protein comprises one or moreamino acids inserted, deleted and / or replaced compared to the wild type protein andoptionallyNunhems Netherlands B.V. 240134WO0154 b) harvesting seed from said cross of step a) and selecting seed comprising said mutantallele.Therefore, in one aspect, a method for producing a Lactuca sativa plant comprising a mutantallele which delays bolting of said plant and / or which causes the plant to be shade tolerant whenthe mutant allele is present in homozygous form is provided, said method comprising the step(s)of: a) crossing a first Lactuca sativa plant and a second Lactuca sativa plant, wherein the first Lactucasativa plant comprises in its genome at least one copy of a mutant allele of the Phytochrome B(LsPhyB) gene, wherein said mutant allele either i) encodes a mutant protein comprising a truncation whereby the protein is truncated in or preceding one of the conserved C-terminal domains of the protein selected from the Modulator Loop, the PAS1-domain, the PAS2-domain, the HKRD-domain and the HATPase Phy-like domain, i.e. in or preceding the Modulator Loop-domain, whereby the remaining amino acids of the C-terminal are missing, in or preceding the PAS1-domain, whereby the remaining amino acids of the C-terminal are missing, or in or preceding the PAS2-domain, whereby the remaining amino acids of the C-terminal are missing, or in or preceding the HKRD-domain whereby the remaining amino acids of the C-terminal are missing, or in or preceding the HATPase Phy-like domain whereby the remaining amino acids of the C-terminal are missing; or ii) encodes a truncated protein, wherein e.g. the final at least 50, 100, 150, 200, 250, 300, 350 C-terminal amino acids are missing; or iii) encodes a mutant protein wherein one or more amino acids of the Modulator Loop domain, the PAS1-domain, the PAS2-domain, the HKRD-domain or the HATPase Phy-like domain are deleted and / or replaced by another amino acid or wherein an amino acid codon in said domain or preceding said domain is mutated into a STOP codon; or iv) encodes a mutant protein wherein one or more amino acids are inserted into the Modulator Loop domain, the PAS1-domain, the PAS2-domain, the HKRD-domain or the HATPase Phy-like domain, b) optionally harvesting seed from the crossing of (a) and selecting seed comprising said mutant allele in its genome.In one aspect a method for producing a Lactuca sativa plant comprising a mutant allele whichdelays bolting of said plant and / or which causes the plant to be shade tolerant when the mutantallele is present in homozygous form is provided, said method comprising the step(s) of:i) crossing a first Lactuca sativa plant and a second Lactuca sativa plant, wherein the first Lactuca sativa plant comprises in its genome at least one copy of a mutant allele of theNunhems Netherlands B.V. 240134WO0155 Phytochrome B (LsPhyB) gene, wherein the mutant allele encodes a mutant protein whereinthe Q amino acid residue at position 750 of SEQ ID NO: 1 (amino acid Q750) or the Q at theequivalent position in a variant comprising at least 95%, 96%, 97%, 98% or 99% identity toSEQ ID NO: 1 is replaced by a different amino acid residue or the codon for said amino acidQ is replaced by a STOP codon, ii) optionally harvesting seed from the crossing of (i) and selecting seed comprising saidmutant allele in its genome. Likewise, the above method is provided wherein the mutant allele under step i) encodes a mutantprotein as described e.g. in Example 6 or elsewhere herein.More preferably, both the first Lactuca sativa plant and the second Lactuca sativa plant in anyone of the method above of producing the Lactuca sativa plant are plants comprises a mutantallele of the LsPhyB gene as described herein in their genome.In one aspect also a plant grown from seeds, or a seed, obtained by any of the methods ofidentifying and / or selecting a Lactuca sativa plant or plant part is provided, wherein said plant orseed comprises a mutant allele of the LsPhyB gene as described herein.Further provided is a method for the growing of a Lactuca sativa plant or producing harvestedplant material (e.g. leaves or heads) of said plant by growing a seed or plant, wherein said seed or plant is homozygous for the mutant allele. In one aspect the seeds or plants comprising the mutant LsPhyB allele in homozygous form aregrown under conditions under which a plant comprising the wild type LsPhyB allele showssymptoms of shade avoidance. This, in one aspect the seeds or plants comprising the mutant LsPhyB allele in homozygous form are grown under conditions under low R:FR light conditions, such as R:FR of equal to or below 0.6, 0.5, 0.4, 0.3, 0.2 or 0.1 and / or under high plant densities, such as equal to or more than at least 200 plants per square meter, e.g. equal to or more than at least 250, 300, 350, 400 or 450 plants per square meter. In one aspect the seeds or plants are grown in a hydroponic system. In one aspect the hydroponic system is automated at least in part, e.g. the sowing, the growing and / or the harvest of the leaves is automated.In one aspect the Lactuca sativa seed or plant comprising the mutant LsPhyB allele inhomozygous form is of the baby-leaf or teen-leaf type.In one aspect a genotyping assay is provided for genotyping lettuce plants, seeds, plant parts,cells or tissues, comprising the steps: a) providing genomic DNA of one or more lettuce plants or a population of plants, andb) carrying out a genotyping assay which detects the presence of the wild type allele of SEQID NO: 5 (or the complement strand thereof) or a wild type allele comprising at least 95%,96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 5 and / or the presence of aNunhems Netherlands B.V. 240134WO0156 mutant allele, wherein the mutant allele comprises one or more nucleotides inserted, deleted, replaced and / or duplicated with respect of SEQ ID NO: 5 or with respect of the wild type allele comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 5, resulting in said mutant allele encoding a mutant protein or a truncated protein as described elsewhere herein, and optionally c) selecting a plant, seed, plant part, cell or tissue comprising e.g. either two copies of thewild type allele, or one copy of the wild type allele and one copy of a mutant allele, or two copies of a mutant allele. Step c) may also be selecting a plant, seed, plant part, cell or tissue comprising at least one copy of a mutant allele.In one aspect, a genotyping assay genotyping lettuce plants, plant parts, cells or tissues,comprising the steps is provided, comprising the steps: a) providing genomic DNA of one or more lettuce plants or a population of plants (e.g.breeding population, F2 population, backcross population etc.), and b) carrying out a genotyping assay which detects the presence of the wild type alleleencoding the protein of SEQ ID NO: 1 (or a wild type allele comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1) and / or the presence of a mutant allele, wherein the mutant allele encodes a protein which comprises one or more amino acids inserted, deleted and / or replaced with respect of SEQ ID NO: 1 (or with respect ofa wild type allele comprising at least 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1), especially as described elsewhere herein, and optionally c) selecting a plant, seed, plant part, cell or tissue comprising either two copies of the wildtype allele, or one copy of the wild type allele and one copy of a mutant allele, or two copies of a mutant allele. Step c) may also be selecting a plant, seed, plant part, cell or tissue comprising at least one copy of a mutant allele. Step a) may comprise isolation of genomic DNA from the plant, seeds, plant part, cell or tissue to be analyzed in the genotyping assay. Often crude DNA extractions methods can be used, as known in the art. Step b) preferably comprises a bi-allelic genotyping assay, which makes use of allele-specific primers and / or allele-specific probes. In one aspect the genotyping assay in step b) discriminates between the wild type PhyB-allele, encoding a protein of SEQ ID NO: 1 or a wild type protein comprising at least 95% identity to SEQ ID NO: 1, and one of the mutant alleles provided or described elsewhere herein, e.g. a mutant allele with one or more amino acids inserted, deleted and / or replaced in one of the C-terminal domains.Nunhems Netherlands B.V. 240134WO0157In a different aspect, a genotyping assay genotyping lettuce plants, plant parts, cells or tissues,comprising the steps is provided, comprising the steps: a) providing genomic DNA of one or more lettuce plants or a population of plants (e.g.breeding population, F2 population, backcross population etc.), and b) carrying out a genotyping assay which detects the presence of the wild type promoter ofSEQ ID NO: 7 (or a wild type promoter comprising at least 90%, 91%, 92%, 93%, 94%,95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1) and / or the presence of amutant promoter, wherein the mutant promoter comprises one or more nucleotidesinserted, deleted and / or replaced with respect of SEQ ID NO: 7 (or with respect of a wildtype promoter comprising at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 7), especially as described elsewhere herein, and optionally c) selecting a plant, seed, plant part, cell or tissue comprising either two copies of the wildtype promoter, or one copy of the wild type promoter and one copy of a mutant promoter,or two copies of a mutant promoter. Various genotyping assays can be used, as long as they can detect INDELs and SNPs and candifferentiate between e.g. the wild type allele of SEQ ID NO: 5 (or a wild type allele comprising atleast 95% sequence identity to SEQ ID NO: 5) being present in the genomic DNA (at the LsPhyBlocus) or a mutant allele of the LsPhyB gene being present in the genomic DNA. The same appliesfor a wild type allele comprising a wild type promoter and a mutant allele comprising a mutant promoter. Genotyping assays may also discriminate between different mutant alleles. Genotyping assays are generally based on allele-specific primers used in PCR or thermal cycling reactions (polymerase chain reaction) to amplify either the wild type or mutant allele and detect the amplification product or on allele-specific oligonucleotide probes, which hybridize to either the wild type allele or the mutant allele, or both. For example genotyping with BHQplus probes uses two allele specific probes and two primers that flank the region of the polymorphism, and during thermal cycling the polymerase encounters the allele-specific probes bound to the DNA and releases a fluorescent signal. Allele discrimination involves competitive binding of the two allele- specific BHQPlus probes (see also biosearchtech.com). Examples of genotyping assays are the KASP-assay (by LGC, see www at LGCgenomics.com and also www at biosearchtech.com / products / pcr-kits-and-reagents / genotyping-assays / kasp- genotyping-chemistry), based on competitive allele-specific PCR and end-point fluorescent detection, the TaqMan-assay (Applied Biosytstems), which is also PCR based, HRM assays (High Resolution Melting Assay), wherein allele-specific probes are detected using real time PCR, or the rhAmp assay, based on Rnase H2-dependent PCR, BHQplus genotyping, BHQplex CoPrimer genotyping and many others. The KASP-assay is also described in He C, Holme J, Anthony J. ‘SNP genotyping: the KASP assay. Methods Mol Biol.2014;1145:75-86’ and EP1726664B1 or US7615620 B2, incorporated by reference. The KASP genotyping assay utilizes a unique form of competitive allele-specific PCR combined with a novel, homogeneous, fluorescence-based reporting system for the identification and measurement of genetic variation occurring at the nucleotide level to detectNunhems Netherlands B.V. 240134WO0158 single nucleotide polymorphisms (SNPs) or inserts and deletions (InDels). The KASP technology is suitable for use on a variety of equipment platforms and provides flexibility in terms of thenumber of SNPs and the number of samples able to be analyzed. The KASP chemistry functionsequally well in 96-, 384-, and 1,536-well microtiter plate formats and has been utilized over many years in large and small laboratories by users across the fields of human, animal, and plant genetics. The TaqMan genotyping assays is also described in Woodward J. ‘Bi-allelic SNP genotyping using the TaqMan® assay.’ Methods Mol Biol.2014;1145:67-74, US5210015 and US5487972,incorporated herein by reference. With TaqMan(®) technology allele-specific probes are utilizedfor quick and reliable genotyping of known polymorphic sites. TaqMan assays are robust in genotyping multiple variant types, including single nucleotide polymorphisms, insertions / deletions, and presence / absence variants. To query a single bi-allelic polymorphism,two TaqMan probes labelled with distinct fluorophores are designed such that they hybridize todifferent alleles during PCR-based amplification of a surrounding target region. During the primer extension phase of PCR, the 5'-3' exonuclease activity of Taq polymerase cleaves and releases the fluorophores from bound probes. At the end of PCR, the emission intensity of each fluorophore is measured and allele determination at the queried site can be made. Various genotyping assays can, therefore, be used, which can differentiate between the presenceof e.g. the wild type allele of the LsPhyB gene, encoding the protein of SEQ ID NO: 1 (or a wildtype protein comprising at least 95% sequence identity to SEQ ID NO: 1), or a mutant allele ofthe LsPhyB gene; or between different mutant alleles of the LsPhyB gene. Various mutant allelesof the LsPhyB gene can be detected. So, not only the mutant allele encoding the proteincomprising an amino acid substitution in one of the conserved domains or a truncation at the C-terminal end, such as the Q750* truncation, but the assay can be designed to detect any othermutant allele of the LsPhyB gene, e.g. any mutant allele described herein.As mentioned preferably a bi-allelic genotyping assay is used, e.g. a KASP-assay, a TaqMan assay, a BHQplus assay, PACE genotyping (see world wide web at idtdna.com / pages / products / qpcr-and-pcr / genotyping / pace-snp-genotyping-assays) or any other bi-allelic genotyping assay. In one aspect the genotyping assay in step b) of the methods above is a KASP-assay. Thus in step b) a competitive PCR is carried out using two forward primers and one common reverseprimer. The two forward primers comprise at least 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20,21, or 22 nucleotides complementary to SEQ ID NO: 5 or complementary to a wild type sequencecomprising at least 95% sequence identity to SEQ ID NO: 5 (or the complement strand of any ofthese). In addition, the two forward primers comprise 1, 2, 3 or more nucleotides (preferably atthe 3’end of the primers) which provide specificity to the SNP or INDEL which differentiates e.g. the wild type sequence from the mutant sequence of the allele. The two forward primers thereby have different binding specificity (or preference) to either the wild type allele or to the mutant allele. A KASP-assay can easily be designed to differentiate between the wild type allele of SEQID NO: 5 (or a wild type sequence comprising at least 95% sequence identity to SEQ ID NO: 5)and any mutant allele of the LsPhyB gene which differs from the wild type allele in one or morenucleotides being inserted, deleted or replaced, so e.g. the assay can be designed for any SNP or INDEL that differentiates two alleles.Nunhems Netherlands B.V. 240134WO0159For example, the amino acid change Q750* is due to codon 2888 to 2890 of SEQ ID NO: 5 beingmutated from CCA to TAA. The mutated nucleotide is thus nucleotide 2888 of SEQ ID NO: 5(mutated from C to T). The two forward KASP primers can then comprise a stretch of nucleotidescomplementary to the sequence preceding the mutated nucleotide plus either the wild type nucleotide (C) or the mutant nucleotide (T). Together with the reverse common primer, they amplify either the wild type allele or the mutant allele in the KASP assay. The genotype is thereby determined for the SNP, either being homozygous wild type, homozygous mutant or heterozygous for mutant and wild type.Thus, in one aspect the SNP (C / T) at nucleotide 2888 of SEQ ID NO: 5 is detected using agenotyping assay, such as a KASP assay, e.g. using two forward primers and a reverse primer.In one aspect the mutant allele of the LsPhyB gene encodes a protein comprising one or moreamino acids inserted, duplicated, replaced and / or deleted with respect of the wild type protein ofSEQ ID NO: 1 (or a wild type protein comprising at least 95% sequence identity to SEQ ID NO:1).In one aspect the mutant allele of the LsPhyB gene encodes a protein which is truncated incomparison to the protein of SEQ ID NO: 1 (or a wild type protein comprising at least 95%sequence identity to SEQ ID NO: 1), e.g. at least the final at least 50, 100, 150, 200, 250, 300,350 or more amino acids are missing at the C-terminal end. The C-terminal end has T1125 aslast amino acid, and when referring to a certain number of amino acids missing at the C-terminalend, it is understood that e.g. at least the final 50, 100, 150 etc. amino acids are missing, whichare counted from amino acid T1125. The remaining part of the truncated protein is not modifiedcompared to the wild type LsPhyB protein sequence of SEQ ID NO: 1 (or a functional variantthereof). Thus, in one aspect the N-terminal region is thus preferably identical to the wild typeLsPhyB protein in truncated proteins. These mutant alleles result in delayed bolting and / or shadetolerance, as e.g. described for the Q750* mutant allele, and plants and seeds comprising one or two copies of any of these mutant alleles are an embodiment herein.In one aspect the mutant allele of the LsPhyB gene encodes a protein which comprises one ormore amino acids deleted and / or replaced in comparison to the protein of SEQ ID NO: 1, e.g. at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more amino acids are deleted and / or replaced by one or more different amino acids, especially in one or more of the conserved domains as described elsewhere herein.In another aspect the mutant allele of the LsPhyB gene encodes a protein which comprises oneor more amino acids inserted or duplicated in comparison to the protein of SEQ ID NO: 1, e.g. at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or more amino acids are inserted or duplicated, especially in one or more of the conserved domains as described elsewhere herein. Therefore, in one embodiment a method is provided for detecting, and optionally selecting, a lettuce plant, seed or plant part comprising at least one copy of a wild type allele and / or of amutant allele of a gene name LsPhyB gene, comprising:a) providing genomic DNA of a lettuce plant or of a plurality of plants (e.g. a breedingpopulation, F2, backcross, etc.),Nunhems Netherlands B.V. 240134WO0160 b) carrying out an assay (e.g. a bi-allelic genotyping assay) that discriminates or can discriminate between the presence of alleles in the genomic DNA of a), based on nucleic acid amplification (e.g. comprising the use of allele specific oligonucleotide primers) and / or nucleic acid hybridization (e.g. comprising the use of allele-specific oligonucleotide probes), to detect the presence of a wild type allele of the gene and / or a mutant allele of the gene, wherein the wild type allele comprises the sequence of SEQ ID NO: 5 (or wherein the wild type allele encodes the protein of SEQ ID NO: 1 or a variant comprising at least 95% identity to SEQ ID NO: 1) and the mutant allele comprises one or more nucleotides inserted, duplicated, deleted or replaced with respect to the sequence of SEQ ID NO: 5 (or the mutant allele encodes aprotein comprising one or more amino acids inserted, duplicated, deleted and / or replaced with respect to the wild type protein of SEQ ID NO: 1 or a variant comprising at least 95% identity to SEQ ID NO: 1), and optionally c) selecting a plant, seed or plant part comprising one or two copies of the mutant allele.The mutant allele detected and optionally selected in any of the above methods is preferably anyof the mutant alleles described herein, e.g. resulting in delayed bolting and / or shade tolerance when in homozygous form, as e.g. the Q750* mutant allele. Under step b) the genotyping assay discriminates between the wild type and the mutant alleles based on nucleic acid (especially DNA) amplification reactions making use of e.g. oligonucleotideprimers, such as PCR (Polymerase Chain Reaction) and PCR primers, preferably allele-specificprimers, and / or nucleic acid hybridization making use of as oligonucleotide probes, preferably allele-specific probes.In one aspect, in any of the above methods the assay uses one or more LsPhyB allele-specificprimers or one or more LsPhyB allele-specific probes. As mentioned, based on the genomicsequence of SEQ ID NO: 5 or other (e.g. degenerate) genomic sequences which encode theprotein of SEQ ID NO: 1 or a variant thereof (e.g. a genomic sequence comprising at least 95%,96%, 97%, 98%, 99% sequence identity to SEQ ID NO: 5) or the genomic sequence of a mutant allele which encodes e.g. a protein comprising one or more amino acids inserted, duplicated, deleted and / or replaced in comparison to SEQ ID NO: 1, PCR primers and nucleic acid probes can be designed using known methods or software programs for oligonucleotide design. Primers and probes may for example be at least 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or more nucleotides (bases) in length and anneal to (or hybridize to) the template DNA sequence, i.e. they preferably have at least 95%, 96%, 97%, 98%, 99% or 100% sequence identity to the target sequence. The primer or probe specificity to a wild type allele or a mutant allele is due to at least 1, 2, 3 or more nucleotides of the primer or probe being specific for either allele. The primers or probes are thus designed around the polymorphism (e.g. the SNP or InDel) between the two alleles of the target gene, so that they discriminate between these. In one aspect the assay is a bi-allelic genotyping assay selected from e.g. a KASP-assay, a TaqMan-assay, a BHQplus probe assay or any other bi-allelic genotyping assay. In one aspect, the mutant allele comprises at least one codon inserted or duplicated in the coding region of the allele, or at least one codon changed into another codon (e.g. through a single nucleotide change), or at least one codon deleted or changed into a STOP codon.Nunhems Netherlands B.V. 240134WO0161 In any of the methods above, in one aspect the mutant allele comprises a nucleotide replaced incodon 2888 to 2889 of SEQ ID NO:5 (e.g. nucleotide 2888 is replaced, e.g. from Cytosine toThymine), leading to the codon for Q750 being a different codon.Thus, in one aspect the methods can be used to discriminate between plants, seeds or plant partscomprising two copies of the wild type LsPhyB allele, two copies of a mutant LsPhyB allele or onecopy of each. Optionally plants, plant parts or seeds comprising any of these genotypes may be selected for e.g. further breeding or for use in lettuce production. Although any DNA genotyping assay may be used in the above methods, be it PCR based (using PCR primers) and / or hybridization based (using probes), in one aspect a KASP-assay is used to discriminate between the wild type and the mutant allele. The assay can be used in a high throughput way, e.g. in 96 well plates or more well plates (e.g.384 well plates). Depending on the SNP or INDEL between the wild type and mutant allele, various allele-specific primers and probes can be designed for use in the assays. In one aspect two forward primers (one for the wild type allele and one for the mutant allele) and one common reverse primer (for both the wild type and the mutant allele) are used in the KASP- assay. In one aspect the two forward primers and the reverse primer comprise at least 10, 11, 12,13, 14, 15, 16, 17, 18, 19 or more nucleotides of SEQ ID NO: 5 or of the complement sequenceof SEQ ID NO: 5. The forward primers further comprise at least 1, 2, or 3 nucleotides (preferably at the 3’end of the primer) which confer specificity (or preference) to either amplification of the wild type allele or amplification of the mutant allele. Each forward primer forms a primer pair with the common reverse primer to amplify the DNA sequence of the target allele in between the primer pair, during thermal cycling. Standard components for thermal cycling are used and standard components for KASP-assays. In one aspect the KASP-assay discriminates between the SNP found between the wild type and mutant allele, i.e. the KASP-assay can discriminate between the presence in the genomic DNAof SEQ ID NO: 5 in homozygous form (LsPhyB wild type, normal bolting allele), and the presenceof e.g. one of the mutant alleles described herein in homozygous form (mutant allele, resulting indelayed bolting and / or shade tolerance). Different forward and reverse primers can be designedto achieve allele discrimination in the assay.Such a genotyping assay can be used for marker assisted selection (MAS) of plants in e.g. abreeding program to select plants comprising a certain genotype, e.g. homozygous for the wild type allele, homozygous or heterozygous for a mutant allele.Therefore, also a method of breeding lettuce plants is provided herein, said method comprisinggenotyping one or more plants for the allele composition at the LsPhyB locus in the genome andoptionally selecting one or more plants having a specific genotype at the LsPhyB locus. In oneaspect also genotyping-by-sequencing may be done for the LsPhyB gene.As mentioned, optionally the plants or seeds which comprise two copies of a mutant LsPhyB allelecan be grown and phenotyped for the delayed bolting phenotype and / or shade toleranceNunhems Netherlands B.V. 240134WO0162 phenotype. The mutant allele is in one aspect a mutant allele which, in homozygous form, confersdelayed bolting and / or shade tolerance.In the above methods either cultivated lettuce Lactuca sativa seeds, plants, plant parts or varieties can be analysed for the allele composition at the LsPhyB-locus, or other species of the genus Lactuca can be analysed.In a different aspect a lettuce, especially Lactuca sativa, plant, seed or plant part is providedcomprising at least one copy of a mutant allele the LsPhyB gene, wherein said mutant alleleencodes a mutant protein comprising one or more amino acids replaced, inserted, duplicated and / or deleted compared to the wild type protein, wherein said mutant allele confers delayedbolting and / or shade tolerance when the mutant allele is in homozygous form (compared to theplant comprising the wild type allele in homozygous form), and wherein the wild type LsPhyBallele encodes a protein of SEQ ID NO: 1 or a protein comprising at least 95%, 96%, 97%, 98%,99% or more sequence identity to SEQ ID NO: 1. SEQUENCES SEQ ID NO: 1 (wild type LsPhyB protein) MASGSKASSG FHPQQVQPQN PSTSSTPRVD SMSKAIAQYA VDARLHAVYE ESGESGKSFD 60 YSHSIKTATD SIAEQQMTAY LSKIQRGGHI QPFGCMIAID NSSFRVIAFS ENARERLGLA 120 PQSVPSLEKT EILTIGTDVK TLFTPSSAIL LERAFRAREI TLLNPVWVHS KNSGKPFYAI 180 LHRIDVGIVI DLEPARTEDP ALSIAGAVQS QKLAVRAISN LQALPGGDIK LLCDTVVQNV 240 RELTGYDRVM VYKFHEDEHG EVVAECKRPD LDPYLGLHYP ATDIPQASRF LFRQNRVRMI 300VDCHANPVPV IQDDCLMQPL CLVGSTLRAP HGCHAQYMAN MGSIASLALA VIINGNEDSG 360 GGRGTMGLWG LVVCHHTSAR CIPFPLRYAC EFLMQAFGLQ LNLELQLASQ MLEKRILRTQ 420 TLLCDMLLRD SPTGIVTQSP SIMDLVKCDG AALFYQGKYY AAGITPTESQ IKDIVEWLLA 480 CHTDSTGLST DSLADAGYPQ AASLGDVVCG MAVAYITSKD FLFWFRSHTA KEMKWGGAKH 540 HPEDKDDGQR MHPRSSFNAF LEVVKSRSLP WENAEMDAIH SLQLILRDSF KEERDSNSKA 600VVKIQSEEMG LQGMDELSSV AKEMVRLIET ATAPIFAVDV EGRINGWNAK IAELTGLSVS 660 EAMGKSLVQD LIFKESQEIV IRLLHHALQG EEDKNVEIKL RTFNLSEEEN AIFVVVNACC 720 SKDYTDNIVG VCFVGQDVTR QKVVMDKFVQ IQGDYRAIVH SPNPLIPPIF ASDENTCCSE 780 WNTAMEKLTG WGRDDVIGKM LVGEIFGSCC RLKGPDSLTK FMIILHNAIS GQDSDKYPFS 840 FFDRRGKFVQ ALLSANKRVN LSGGDATGAF CFLQIASPEL QQALKIQRQQ ENKCFARMKE 900LAYICHEIKS PLSGIRFANL LLEATDLSED QKQLLETSAA CEKQMLKIIK DVDMENIQEG 960 HLEVEKREFV VGSVIDAVVS QVMLILRDRG VQLIRDIPEE VKTLTVCGDQ TRVQQVLTNF 1020 LLNMVQHSPS PNGWVEIQVR PSLKQVFDGI TNAHIEFRMV CPGNGLPAEL VQDMFQSSQW 1080 STEEGLGLSM CRKILKLMNG EVQYIRESER CYFHIVIELP LPRGT 1125 SEQ ID NO: 2 (Q750* mutant LsPhyB protein) MASGSKASSG FHPQQVQPQN PSTSSTPRVD SMSKAIAQYA VDARLHAVYE ESGESGKSFD 60 YSHSIKTATD SIAEQQMTAY LSKIQRGGHI QPFGCMIAID NSSFRVIAFS ENARERLGLA 120 PQSVPSLEKT EILTIGTDVK TLFTPSSAIL LERAFRAREI TLLNPVWVHS KNSGKPFYAI 180LHRIDVGIVI DLEPARTEDP ALSIAGAVQS QKLAVRAISN LQALPGGDIK LLCDTVVQNV 240 RELTGYDRVM VYKFHEDEHG EVVAECKRPD LDPYLGLHYP ATDIPQASRF LFRQNRVRMI 300 VDCHANPVPV IQDDCLMQPL CLVGSTLRAP HGCHAQYMAN MGSIASLALA VIINGNEDSG 360 GGRGTMGLWG LVVCHHTSAR CIPFPLRYAC EFLMQAFGLQ LNLELQLASQ MLEKRILRTQ 420Nunhems Netherlands B.V. 240134WO0163 TLLCDMLLRD SPTGIVTQSP SIMDLVKCDG AALFYQGKYY AAGITPTESQ IKDIVEWLLA 480 CHTDSTGLST DSLADAGYPQ AASLGDVVCG MAVAYITSKD FLFWFRSHTA KEMKWGGAKH 540 HPEDKDDGQR MHPRSSFNAF LEVVKSRSLP WENAEMDAIH SLQLILRDSF KEERDSNSKA 600 VVKIQSEEMG LQGMDELSSV AKEMVRLIET ATAPIFAVDV EGRINGWNAK IAELTGLSVS 660 EAMGKSLVQD LIFKESQEIV IRLLHHALQG EEDKNVEIKL RTFNLSEEEN AIFVVVNACC 720SKDYTDNIVG VCFVGQDVTR QKVVMDKFV 749 SEQ ID NO: 3 (cDNA encoding the wild type LsPhyB protein of SEQ ID NO: 1); CAA codon encoding Q750 is highlighted in box atggcttctg ggagcaaagc aagttctggg tttcacccac aacaagttca acctcaaaac 60ccttctacat catcaacgcc tagggttgat tcaatgagta aagccattgc acaatacgca 120 gtcgatgcta gattacacgc tgtttatgaa gaatccggtg aatctggtaa gtcttttgat 180 tactcacact caatcaaaac agccaccgat tcaatcgctg aacaacaaat gactgcttat 240 ctatccaaaa ttcaaagagg tggtcacatt caaccctttg gttgtatgat tgctatcgat 300 aattctagtt ttagagtaat tgcgttcagt gaaaatgcta gagaacgatt aggtttagca 360ccacaatccg ttcctagtct ggaaaaaacc gaaattttaa caattggaac tgatgtcaaa 420 acccttttca ccccttcgag tgctatattg ctggaaaggg ctttccgggc tcgcgaaatt 480 accctcttaa accctgtctg ggttcactcc aagaattccg gtaaaccatt ttacgcgatt 540 ctgcacagaa tcgatgttgg tatagttatc gatttggaac ctgctagaac cgaggatcct 600 gctttatcaa ttgctggggc tgttcaatct cagaagctcg ctgttcgagc catttcaaat 660ttacaggcgt tgccaggtgg cgatattaag cttctgtgtg acaccgttgt acaaaacgtg 720 agagagctca ctggttacga tcgtgtaatg gtctacaagt ttcacgaaga tgaacatggt 780 gaagtggtgg cggaatgcaa gaggcctgat ttggatcctt atctcgggtt acattatccc 840 gcaactgata tcccacaggc ttcaagattc ttgtttaggc agaatcgtgt cagaatgata 900 gttgattgtc acgctaaccc tgttcctgta atccaagacg attgtttgat gcagcctttg 960tgtttagtag ggtccaccct tcgggcccct catggttgcc atgctcaata catggctaac 1020 atgggttcaa tagcttcatt agctttggca gtaatcatca atggaaacga agattccgga 1080 ggtgggagag ggacaatggg gctatggggg ttagtagttt gtcaccatac atcggcacga 1140 tgcattccgt ttccattacg ttacgcgtgt gaattcttga tgcaagcttt tggactccaa 1200 ctaaacttgg aattacaatt agcttctcaa atgttggaaa aacggattct aagaacacaa 1260actttgttat gtgatatgct cctacgtgat tcccctaccg gaatcgtgac tcaaagtcca 1320 agcatcatgg atcttgtgaa atgtgatggt gctgctcttt tttaccaagg aaagtactat 1380 gcggccggaa tcacaccaac ggaatcacaa atcaaagata tagtggaatg gctattggca 1440 tgtcataccg attccaccgg tttaagcacc gattcattag cggatgccgg ttaccctcaa 1500 gctgcttcac ttggtgatgt ggtttgtggg atggcagttg cttatataac ttcaaaagat 1560ttcttgtttt ggttccggtc ccacactgca aaagagatga aatggggtgg agctaaacat 1620 catccggaag ataaagatga tgggcaacga atgcatccac gttcttcatt caacgcgttt 1680 cttgaagttg tgaagagtag aagcttgcca tgggagaatg ctgaaatgga tgcaatccat 1740 tctttacaac ttattttaag agattcgttt aaagaagaac gtgattccaa ttccaaagct 1800 gtagtcaaga ttcaaagtga ggaaatgggg ttgcagggaa tggatgaact tagttcggtt 1860gcaaaagaaa tggttcgatt gattgaaact gcaactgctc ccatatttgc tgttgatgtt 1920 gaaggaagaa taaacggatg gaatgcaaag attgcagagt tgactggtct ttcggttagt 1980 gaagctatgg ggaaatcatt ggttcaagat ctcattttta aagagtcaca agaaatcgtc 2040 atcaggcttc ttcatcatgc tttacaaggt gaagaagaca agaacgtgga gatcaaactc 2100 cgaacattca atttatcaga agaagaaaac gcgatatttg tagtggtgaa tgcttgttgt 2160agcaaagact atacagacaa catcgttgga gtttgtttcg tgggtcaaga tgtaacgaga 2220 caaaaagtcg taatggacaa attcgtccaa attcaaggcg attatcgggc cattgtacat 2280Nunhems Netherlands B.V. 240134WO0164 agtccaaatc ccttaatccc acccatcttt gcatccgatg aaaacacatg ttgctcagaa 2340 tggaacaccg ctatggaaaa actcacaggg tgggggagag atgatgtcat cgggaaaatg 2400 ttggttgggg agatttttgg aagttgttgt cgcctaaagg gtccggattc tttaacaaaa 2460 ttcatgatca ttttgcataa tgcaattagt ggacaagata gcgataagta tccgttttca 2520 ttctttgatc gacgtgggaa atttgttcaa gctttgttgt ccgcaaacaa aagggtaaat 2580ttgtccggtg gtgatgctac aggggcgttt tgtttcttgc aaatcgcaag ccccgagcta 2640 caacaagctt taaagataca aagacaacaa gagaacaaat gttttgcaag aatgaaagaa 2700 ttagcgtata tttgtcatga aatcaagagt ccattaagtg ggattcgctt tgctaatttg 2760 cttcttgaag ctacggattt gtccgaagat caaaagcagt tgttggaaac cagcgcagct 2820 tgtgagaaac aaatgttgaa gattataaaa gatgttgata tggagaacat tcaagaagga 2880catttggagg ttgaaaagcg ggagtttgtg gttgggagtg tgatcgatgc ggtggttagc 2940 caagtgatgt tgatattgag ggatcgaggg gtgcaattga ttcgggatat tccggaagaa 3000 gtcaaaacgt tgactgtttg tggtgatcaa actagggttc aacaagtgtt gactaatttc 3060 ttgttgaata tggttcaaca ttcgccttcg cctaatggtt gggttgaaat tcaggttcga 3120 cccagtttga agcaggtttt tgatggaatc accaatgccc atattgagtt taggatggtg 3180tgcccgggaa acggtcttcc agctgagctg gttcaagaca tgtttcagag cagtcagtgg 3240 agcacagagg aaggtttagg attaagcatg tgtaggaaga tcttaaagct aatgaatgga 3300 gaggttcaat atataagaga atctgaaagg tgttatttcc atattgtgat tgaactccct 3360 cttcctcgtg gaacatga 3378 SEQ ID NO: 4 (cDNA encoding the mutant LsPhyB protein of SEQ ID NO: 2) atggcttctg ggagcaaagc aagttctggg tttcacccac aacaagttca acctcaaaac 60 ccttctacat catcaacgcc tagggttgat tcaatgagta aagccattgc acaatacgca 120 gtcgatgcta gattacacgc tgtttatgaa gaatccggtg aatctggtaa gtcttttgat 180 tactcacact caatcaaaac agccaccgat tcaatcgctg aacaacaaat gactgcttat 240ctatccaaaa ttcaaagagg tggtcacatt caaccctttg gttgtatgat tgctatcgat 300 aattctagtt ttagagtaat tgcgttcagt gaaaatgcta gagaacgatt aggtttagca 360 ccacaatccg ttcctagtct ggaaaaaacc gaaattttaa caattggaac tgatgtcaaa 420 acccttttca ccccttcgag tgctatattg ctggaaaggg ctttccgggc tcgcgaaatt 480 accctcttaa accctgtctg ggttcactcc aagaattccg gtaaaccatt ttacgcgatt 540ctgcacagaa tcgatgttgg tatagttatc gatttggaac ctgctagaac cgaggatcct 600 gctttatcaa ttgctggggc tgttcaatct cagaagctcg ctgttcgagc catttcaaat 660 ttacaggcgt tgccaggtgg cgatattaag cttctgtgtg acaccgttgt acaaaacgtg 720 agagagctca ctggttacga tcgtgtaatg gtctacaagt ttcacgaaga tgaacatggt 780 gaagtggtgg cggaatgcaa gaggcctgat ttggatcctt atctcgggtt acattatccc 840gcaactgata tcccacaggc ttcaagattc ttgtttaggc agaatcgtgt cagaatgata 900 gttgattgtc acgctaaccc tgttcctgta atccaagacg attgtttgat gcagcctttg 960 tgtttagtag ggtccaccct tcgggcccct catggttgcc atgctcaata catggctaac 1020 atgggttcaa tagcttcatt agctttggca gtaatcatca atggaaacga agattccgga 1080 ggtgggagag ggacaatggg gctatggggg ttagtagttt gtcaccatac atcggcacga 1140tgcattccgt ttccattacg ttacgcgtgt gaattcttga tgcaagcttt tggactccaa 1200 ctaaacttgg aattacaatt agcttctcaa atgttggaaa aacggattct aagaacacaa 1260 actttgttat gtgatatgct cctacgtgat tcccctaccg gaatcgtgac tcaaagtcca 1320 agcatcatgg atcttgtgaa atgtgatggt gctgctcttt tttaccaagg aaagtactat 1380 gcggccggaa tcacaccaac ggaatcacaa atcaaagata tagtggaatg gctattggca 1440tgtcataccg attccaccgg tttaagcacc gattcattag cggatgccgg ttaccctcaa 1500 gctgcttcac ttggtgatgt ggtttgtggg atggcagttg cttatataac ttcaaaagat 1560Nunhems Netherlands B.V. 240134WO0165 ttcttgtttt ggttccggtc ccacactgca aaagagatga aatggggtgg agctaaacat 1620 catccggaag ataaagatga tgggcaacga atgcatccac gttcttcatt caacgcgttt 1680 cttgaagttg tgaagagtag aagcttgcca tgggagaatg ctgaaatgga tgcaatccat 1740 tctttacaac ttattttaag agattcgttt aaagaagaac gtgattccaa ttccaaagct 1800 gtagtcaaga ttcaaagtga ggaaatgggg ttgcagggaa tggatgaact tagttcggtt 1860gcaaaagaaa tggttcgatt gattgaaact gcaactgctc ccatatttgc tgttgatgtt 1920 gaaggaagaa taaacggatg gaatgcaaag attgcagagt tgactggtct ttcggttagt 1980 gaagctatgg ggaaatcatt ggttcaagat ctcattttta aagagtcaca agaaatcgtc 2040 atcaggcttc ttcatcatgc tttacaaggt gaagaagaca agaacgtgga gatcaaactc 2100 cgaacattca atttatcaga agaagaaaac gcgatatttg tagtggtgaa tgcttgttgt 2160agcaaagact atacagacaa catcgttgga gtttgtttcg tgggtcaaga tgtaacgaga 2220 caaaaagtcg taatggacaa attcgtctaa 2250 SEQ ID NO: 5 (genomic DNA encoding the wild type LsPhyB protein of SEQID NO: 1; CAA at 2888 – 2890 is codon for Q750)atggcttctg ggagcaaagc aagttctggg tttcacccac aacaagttca acctcaaaac 60 ccttctacat catcaacgcc tagggttgat tcaatgagta aagccattgc acaatacgca 120 gtcgatgcta gattacacgc tgtttatgaa gaatccggtg aatctggtaa gtcttttgat 180 tactcacact caatcaaaac agccaccgat tcaatcgctg aacaacaaat gactgcttat 240 ctatccaaaa ttcaaagagg tggtcacatt caaccctttg gttgtatgat tgctatcgat 300aattctagtt ttagagtaat tgcgttcagt gaaaatgcta gagaacgatt aggtttagca 360 ccacaatccg ttcctagtct ggaaaaaacc gaaattttaa caattggaac tgatgtcaaa 420 acccttttca ccccttcgag tgctatattg ctggaaaggg ctttccgggc tcgcgaaatt 480 accctcttaa accctgtctg ggttcactcc aagaattccg gtaaaccatt ttacgcgatt 540 ctgcacagaa tcgatgttgg tatagttatc gatttggaac ctgctagaac cgaggatcct 600gctttatcaa ttgctggggc tgttcaatct cagaagctcg ctgttcgagc catttcaaat 660 ttacaggcgt tgccaggtgg cgatattaag cttctgtgtg acaccgttgt acaaaacgtg 720 agagagctca ctggttacga tcgtgtaatg gtctacaagt ttcacgaaga tgaacatggt 780 gaagtggtgg cggaatgcaa gaggcctgat ttggatcctt atctcgggtt acattatccc 840 gcaactgata tcccacaggc ttcaagattc ttgtttaggc agaatcgtgt cagaatgata 900gttgattgtc acgctaaccc tgttcctgta atccaagacg attgtttgat gcagcctttg 960 tgtttagtag ggtccaccct tcgggcccct catggttgcc atgctcaata catggctaac 1020 atgggttcaa tagcttcatt agctttggca gtaatcatca atggaaacga agattccgga 1080 ggtgggagag ggacaatggg gctatggggg ttagtagttt gtcaccatac atcggcacga 1140 tgcattccgt ttccattacg ttacgcgtgt gaattcttga tgcaagcttt tggactccaa 1200ctaaacttgg aattacaatt agcttctcaa atgttggaaa aacggattct aagaacacaa 1260 actttgttat gtgatatgct cctacgtgat tcccctaccg gaatcgtgac tcaaagtcca 1320 agcatcatgg atcttgtgaa atgtgatggt gctgctcttt tttaccaagg aaagtactat 1380 gcggccggaa tcacaccaac ggaatcacaa atcaaagata tagtggaatg gctattggca 1440 tgtcataccg attccaccgg tttaagcacc gattcattag cggatgccgg ttaccctcaa 1500gctgcttcac ttggtgatgt ggtttgtggg atggcagttg cttatataac ttcaaaagat 1560 ttcttgtttt ggttccggtc ccacactgca aaagagatga aatggggtgg agctaaacat 1620 catccggaag ataaagatga tgggcaacga atgcatccac gttcttcatt caacgcgttt 1680 cttgaagttg tgaagagtag aagcttgcca tgggagaatg ctgaaatgga tgcaatccat 1740 tctttacaac ttattttaag agattcgttt aaagaagaac gtgattccaa ttccaaagct 1800gtagtcaaga ttcaaagtga ggaaatgggg ttgcagggaa tggatgaact tagttcggtt 1860 gcaaaagaaa tggttcgatt gattgaaact gcaactgctc ccatatttgc tgttgatgtt 1920Nunhems Netherlands B.V. 240134WO0166 gaaggaagaa taaacggatg gaatgcaaag attgcagagt tgactggtct ttcggttagt 1980 gaagctatgg ggaaatcatt ggttcaagat ctcattttta aagagtcaca agaaatcgtc 2040 atcaggcttc ttcatcatgc tttacaaggt acttctttat gtcctctcca tcattccaac 2100 atttcatggt ttcaaagttt cttgtctttt gatgtcaaga tttcaagatt gcaaagtgtc 2160 ttgattttta atgccaagat ttcaaaattg caaactttct tgcttttcaa tgccatgatt 2220tcaagttgca aagtttatat cttttttttt tcataccaag atttcaagat tgcaaagttt 2280 cctgcttttt aatgccaata ttcaagattg caattaaaga ttcttgctta ttatgccaag 2340 atttcaagat ttcaaagttt cctgctcttt cctctcttta acccacaaac aataatcaca 2400 tgcacttgac aacaagtcat taattctgtt atatacactg ttttcactgt ttttcaatgc 2460 cacaaacaga ttttagataa tacaagatca actttaatct ctttaaaatt atgctattat 2520agtatactat gaatttaagg tccaaaaaac ttttaagaac cccttgtcgt cccaaaagca 2580 atgatcactt tgttgttaga aagttgttca tgcagttgta tactctgttt tctctgtttc 2640 ttcccacaac aaaaagatct tgttgttttc ttgtgaacat acacacttat tttgctttga 2700 cataataggt gaagaagaca agaacgtgga gatcaaactc cgaacattca atttatcaga 2760 agaagaaaac gcgatatttg tagtggtgaa tgcttgttgt agcaaagact atacagacaa 2820catcgttgga gtttgtttcg tgggtcaaga tgtaacgaga caaaaagtcg taatggacaa 2880 attcgtccaa attcaaggcg attatcgggc cattgtacat agtccaaatc ccttaatccc 2940 acccatcttt gcatccgatg aaaacacatg ttgctcagaa tggaacaccg ctatggaaaa 3000 actcacaggg tgggggagag atgatgtcat cgggaaaatg ttggttgggg agatttttgg 3060 aagttgttgt cgcctaaagg gtccggattc tttaacaaaa ttcatgatca ttttgcataa 3120tgcaattagt ggacaagata gcgataagta tccgttttca ttctttgatc gacgtgggaa 3180 atttgttcaa gctttgttgt ccgcaaacaa aagggtaaat ttgtccggtg gtgatgctac 3240 aggggcgttt tgtttcttgc aaatcgcaag ccccgagcta caacaagctt taaagataca 3300 aagacaacaa gagaacaaat gttttgcaag aatgaaagaa ttagcgtata tttgtcatga 3360 aatcaagagt ccattaagtg ggattcgctt tgctaatttg cttcttgaag ctacggattt 3420gtccgaagat caaaagcagt tgttggaaac cagcgcagct tgtgagaaac aaatgttgaa 3480 gattataaaa gatgttgata tggagaacat tcaagaaggg tgagttacgt taggattata 3540 ctactatgtt gttacatttg tagaaacaaa taatataata tgaatatgat cttgtgttgg 3600 cagacatttg gaggttgaaa agcgggagtt tgtggttggg agtgtgatcg atgcggtggt 3660 tagccaagtg atgttgatat tgagggatcg aggggtgcaa ttgattcggg atattccgga 3720agaagtcaaa acgttgactg tttgtggtga tcaaactagg gttcaacaag tgttgactaa 3780 tttcttgttg aatatggttc aacattcgcc ttcgcctaat ggttgggttg aaattcaggt 3840 tcgacccagt ttgaagcagg tttttgatgg aatcaccaat gcccatattg agtttaggta 3900 tttcatttca tcttgctttc tttttttaaa attttttttt ttaaaaaaaa atttggtttt 3960 tatttttgtc aggatggtgt gcccgggaaa cggtcttcca gctgagctgg ttcaagacat 4020gtttcagagc agtcagtgga gcacagagga aggtttagga ttaagcatgt gtaggaagat 4080 cttaaagcta atgaatggag aggttcaata tataagagaa tctgaaaggt gttatttcca 4140 tattgtgatt gaactccctc ttcctcgtgg aacatga 4177 SEQ ID NO: 6 (genomic DNA encoding the mutant LsPhyB protein of SEQ IDNO: 2; TAA at 2888 – 2890 is translation STOP codon)atggcttctg ggagcaaagc aagttctggg tttcacccac aacaagttca acctcaaaac 60 ccttctacat catcaacgcc tagggttgat tcaatgagta aagccattgc acaatacgca 120 gtcgatgcta gattacacgc tgtttatgaa gaatccggtg aatctggtaa gtcttttgat 180tactcacact caatcaaaac agccaccgat tcaatcgctg aacaacaaat gactgcttat 240 ctatccaaaa ttcaaagagg tggtcacatt caaccctttg gttgtatgat tgctatcgat 300Nunhems Netherlands B.V. 240134WO0167 aattctagtt ttagagtaat tgcgttcagt gaaaatgcta gagaacgatt aggtttagca 360 ccacaatccg ttcctagtct ggaaaaaacc gaaattttaa caattggaac tgatgtcaaa 420 acccttttca ccccttcgag tgctatattg ctggaaaggg ctttccgggc tcgcgaaatt 480 accctcttaa accctgtctg ggttcactcc aagaattccg gtaaaccatt ttacgcgatt 540ctgcacagaa tcgatgttgg tatagttatc gatttggaac ctgctagaac cgaggatcct 600gctttatcaa ttgctggggc tgttcaatct cagaagctcg ctgttcgagc catttcaaat 660 ttacaggcgt tgccaggtgg cgatattaag cttctgtgtg acaccgttgt acaaaacgtg 720 agagagctca ctggttacga tcgtgtaatg gtctacaagt ttcacgaaga tgaacatggt 780 gaagtggtgg cggaatgcaa gaggcctgat ttggatcctt atctcgggtt acattatccc 840gcaactgata tcccacaggc ttcaagattc ttgtttaggc agaatcgtgt cagaatgata 900gttgattgtc acgctaaccc tgttcctgta atccaagacg attgtttgat gcagcctttg 960 tgtttagtag ggtccaccct tcgggcccct catggttgcc atgctcaata catggctaac 1020 atgggttcaa tagcttcatt agctttggca gtaatcatca atggaaacga agattccgga 1080 ggtgggagag ggacaatggg gctatggggg ttagtagttt gtcaccatac atcggcacga 1140tgcattccgt ttccattacg ttacgcgtgt gaattcttga tgcaagcttt tggactccaa 1200ctaaacttgg aattacaatt agcttctcaa atgttggaaa aacggattct aagaacacaa 1260 actttgttat gtgatatgct cctacgtgat tcccctaccg gaatcgtgac tcaaagtcca 1320 agcatcatgg atcttgtgaa atgtgatggt gctgctcttt tttaccaagg aaagtactat 1380 gcggccggaa tcacaccaac ggaatcacaa atcaaagata tagtggaatg gctattggca 1440tgtcataccg attccaccgg tttaagcacc gattcattag cggatgccgg ttaccctcaa 1500gctgcttcac ttggtgatgt ggtttgtggg atggcagttg cttatataac ttcaaaagat 1560 ttcttgtttt ggttccggtc ccacactgca aaagagatga aatggggtgg agctaaacat 1620 catccggaag ataaagatga tgggcaacga atgcatccac gttcttcatt caacgcgttt 1680 cttgaagttg tgaagagtag aagcttgcca tgggagaatg ctgaaatgga tgcaatccat 1740tctttacaac ttattttaag agattcgttt aaagaagaac gtgattccaa ttccaaagct 1800gtagtcaaga ttcaaagtga ggaaatgggg ttgcagggaa tggatgaact tagttcggtt 1860 gcaaaagaaa tggttcgatt gattgaaact gcaactgctc ccatatttgc tgttgatgtt 1920 gaaggaagaa taaacggatg gaatgcaaag attgcagagt tgactggtct ttcggttagt 1980 gaagctatgg ggaaatcatt ggttcaagat ctcattttta aagagtcaca agaaatcgtc 2040atcaggcttc ttcatcatgc tttacaaggt acttctttat gtcctctcca tcattccaac 2100atttcatggt ttcaaagttt cttgtctttt gatgtcaaga tttcaagatt gcaaagtgtc 2160 ttgattttta atgccaagat ttcaaaattg caaactttct tgcttttcaa tgccatgatt 2220 tcaagttgca aagtttatat cttttttttt tcataccaag atttcaagat tgcaaagttt 2280 cctgcttttt aatgccaata ttcaagattg caattaaaga ttcttgctta ttatgccaag 2340atttcaagat ttcaaagttt cctgctcttt cctctcttta acccacaaac aataatcaca 2400tgcacttgac aacaagtcat taattctgtt atatacactg ttttcactgt ttttcaatgc 2460 cacaaacaga ttttagataa tacaagatca actttaatct ctttaaaatt atgctattat 2520 agtatactat gaatttaagg tccaaaaaac ttttaagaac cccttgtcgt cccaaaagca 2580 atgatcactt tgttgttaga aagttgttca tgcagttgta tactctgttt tctctgtttc 2640ttcccacaac aaaaagatct tgttgttttc ttgtgaacat acacacttat tttgctttga 2700cataataggt gaagaagaca agaacgtgga gatcaaactc cgaacattca atttatcaga 2760 agaagaaaac gcgatatttg tagtggtgaa tgcttgttgt agcaaagact atacagacaa 2820 catcgttgga gtttgtttcg tgggtcaaga tgtaacgaga caaaaagtcg taatggacaa 2880 attcgtctaa attcaaggcg attatcgggc cattgtacat agtccaaatc ccttaatccc 2940acccatcttt gcatccgatg aaaacacatg ttgctcagaa tggaacaccg ctatggaaaa 3000actcacaggg tgggggagag atgatgtcat cgggaaaatg ttggttgggg agatttttgg 3060 aagttgttgt cgcctaaagg gtccggattc tttaacaaaa ttcatgatca ttttgcataa 3120Nunhems Netherlands B.V. 240134WO0168 tgcaattagt ggacaagata gcgataagta tccgttttca ttctttgatc gacgtgggaa 3180 atttgttcaa gctttgttgt ccgcaaacaa aagggtaaat ttgtccggtg gtgatgctac 3240 aggggcgttt tgtttcttgc aaatcgcaag ccccgagcta caacaagctt taaagataca 3300 aagacaacaa gagaacaaat gttttgcaag aatgaaagaa ttagcgtata tttgtcatga 3360 aatcaagagt ccattaagtg ggattcgctt tgctaatttg cttcttgaag ctacggattt 3420gtccgaagat caaaagcagt tgttggaaac cagcgcagct tgtgagaaac aaatgttgaa 3480 gattataaaa gatgttgata tggagaacat tcaagaaggg tgagttacgt taggattata 3540 ctactatgtt gttacatttg tagaaacaaa taatataata tgaatatgat cttgtgttgg 3600 cagacatttg gaggttgaaa agcgggagtt tgtggttggg agtgtgatcg atgcggtggt 3660 tagccaagtg atgttgatat tgagggatcg aggggtgcaa ttgattcggg atattccgga 3720agaagtcaaa acgttgactg tttgtggtga tcaaactagg gttcaacaag tgttgactaa 3780 tttcttgttg aatatggttc aacattcgcc ttcgcctaat ggttgggttg aaattcaggt 3840 tcgacccagt ttgaagcagg tttttgatgg aatcaccaat gcccatattg agtttaggta 3900 tttcatttca tcttgctttc tttttttaaa attttttttt ttaaaaaaaa atttggtttt 3960 tatttttgtc aggatggtgt gcccgggaaa cggtcttcca gctgagctgg ttcaagacat 4020gtttcagagc agtcagtgga gcacagagga aggtttagga ttaagcatgt gtaggaagat 4080 cttaaagcta atgaatggag aggttcaata tataagagaa tctgaaaggt gttatttcca 4140 tattgtgatt gaactccctc ttcctcgtgg aacatga 4177 SEQ ID NO: 7 (promoter of the LsPhyB gene) ctcaagggaa catacatgat ttagttcaga aaatttaatt tttaattaac ctaataatag 60 ttaagcatgc aatggatatt agttgctatt cattgatttc tatactaatt aagcctattg 120 gttcgattat aaccctaatg attataagga caactaacac aatgataata taatttatta 180 ccattatttt cagtcttata gtttgtatca tgaaagattt gatctggatt gatctcaatg 240gtcatagaaa atcaactgct gcacataata gtcatcatat gcaattcata cacattagag 300 ttcattactg tattaaccta acaatagaat ttggtccatc atcagtcata attgttcatg 360 gtcattaaca attataattc aagcaaatac aatttgattg gtcctacaaa ctatatttac 420 tcaacaatag aaaataaata tatataaact tgaacacata tgaatttttg attaaacaag 480 cacaataaat gaaataactc aaaatatcca aacaataatc aatcaaaatc ttaaaggttt 540atctacatct aatcaaaagc aaaatggttt ttaagcccaa aatatgaagt agaaaacata 600 aggaaattat aaaaaaaatg ataaacatgg ttagaaaagc aaaccaaata acatctgtaa 660 cgattttgct catgatcctt catattcccg ctcctagcca acctttcagc ctcaacacac 720 cttctggact ctcaaaacgg atgctctctg atgtattttt gatctatgag ttcagatatg 780 cctcctaggt caagataatg cattatttat agatttttct gttgaactat ttacatggtg 840tgcgagtcag ttggatgcaa cacatagtta gatgaatccg agtataaatt gaactcttga 900 tttcggcata caagaagcat gtaggtggcg cataattgat tgatttccct tttccaactt 960 cttttatctc gacatagaat tcaacttcag ttttcttcct aactctaaca tctctattaa 1020 tatgcaaaat atcaattcaa agctttataa gcacctcata gcttcaaatg catcaaaata 1080 caactcacaa cattaagata ttactcttaa tgtatttata catataacaa tatcatattt 1140tttcaccggt atacgtggcc tagctacaag ggctctttac taccccggta ctcggtaata 1200 ccatgagcat gacaaaagtt aatgttataa tgatgctaaa taaagtagaa ttgaaaagga 1260 agtacgtaaa ctatagaaat gactacctct tgccatgcat atgatcaata tccctctcgg 1320 tgacctcatc atcaaatgag tcatataaac aagtcaaaca ccttgcaatt tgaaactgaa 1380 aaaacgatat taattaataa tcataaaagc aattttcata aagtccaccg tttcgcagtt 1440gcccactcct acatgactac ggagaaagat agaagctaaa ctatgttaag gcatttcatt 1500 agccatgatg actataatta tcattttctt ttatttattt atataattta attttatatt 1560Nunhems Netherlands B.V. 240134WO0169 atattaaatt attcaacaaa ctttcttttt acaagtacaa ctatgtatta agtcgttata 1620 aaaattaaat ttcgttatgt aagttactaa aattttaata gcatattgtt cacatgttaa 1680 aattaaattc atatttaatt aaaataaatt aaaacatata tatatatata tatatatata 1740 tatatatata tatatatata tatatatata tatatatata tatatatata tatatatata 1800 tatatatata tatatatata tatatatata tatatatata tatatatata tatatatata 1860tatatatata ttattttcta taaagttgcg atgtaatgag atcagatgag atgtggagag 1920 aatccaggac tgaatgacta taaatgcaac caaagcttca aaccaacacc tcaaatccac 1980 cacaagtata cttgtaaacc tcatcgctcc cttcttgatc ttgttgttaa tcaccaaaac 2040 tgcatttaat ctttcatccc caattccaaa ttcattcaag attcataaac 2090 SEQ ID NO: 8 (Cucumber, Cucumis sativus, wild type CsPhyB protein) MVSSNRATHS HQQQAQSSNT NTSNLRSHRT DSISKAIAQY TVDARLHAVF EQSGESGKSF 60 DYSQSIKTST QSVPEQQITA YLSKIQRGGH IQPFGCMIAI EEASFRVIAY SENARELLGL 120 TPQSVPSLEK PEILTIGTDV RNLFTSNSAI LLEKAFGARE ITLLNPVWIH SKNSGKPFYA 180 ILHRIDVGIV IDLEPARTED PALSIAGAVQ SQKLAVRAIS QLQALPGGDI KLLCDTVVES 240VRELTGYDRV MVYKFHEDEH GEVVAESKRP DLEPYIGLHY PSTDIPQASR FLFKQNRVRM 300 IVDCHASPVR VIQDAGLMQH LCLVGSTLRA PHGCHAQYMA NMGSIASLAM AVVINGNDDE 360 AIGGRNSTRL WGLVVCHHTS ARCIPFPLRY ACEFLMQAFG LQLNMELQLA SQLSEKHVLR 420 TQTLLCDMLL RDSPAGIVTQ SPSIMDLVKC DGAALYYQGK YYPLGVTPTE AQIKDIVEWL 480 LAFHGDSTGL STDSLADAGY PGAALLGDAV CGMAVAYITK KDFLFWFRSH TAKEIKWGGA 540KHHPEDKDDG QRMHPRSSFK AFLEVVKSRS LPWENAEMDA IHSLQLILRD SFKNDVAINS 600 KAVVHPHLGD LDLQGIDELS SVAREMVRLI ETATAPIFAV DADGRINGWN AKIAELTGLA 660 VEEAMGKSLV RDLVYKESEE TVDRLVSRAL KGEEDKNIEI KMRTFGPEED QRTPFFVVVN 720 ACSSRDYTDN IVGVCFVGQD VTCQKVFMDK FVSIQGDYKA IIHSPNPLIP PIFASDDNTC 780 CSEWNTAMEK LTGWSREDII GKMLVGEVFG SCCRLKGPDA LTKFMIVLHS AIGGQDNEKY 840PFSFYDKKGK YVQALLTANK RMNMEGQIVG AFCFLQIASP ELQQTLRMQR QQEKNRFARM 900 KELAYICQEV KSPLSGIRFT NSLLEATDLS EDQKQFLETS VACEKQMLKI IEDMDLECID 960 DGTMELEKGE FLLGSVINAV VSQVMILLRE RSLQLIRDIP EEVKTMAVYG DQVRIQQVLA 1020 DFLLNMVRYA PSPEGWVEIR VCPLLKQNSD GITLAHTEFR IVCPGEGLPP ELVQDMFHSG 1080 RWVTQEGLGL SMCRKILKLM NGEVQYIRES ERCYFLITLE LPLTERGLND VG 1132SEQ ID NO: 9 (Arabidopsis thaliana wild type AtPhyB protein) MVSGVGGSGG GRGGGRGGEE EPSSSHTPNN RRGGEQAQSS GTKSLRPRSN TESMSKAIQQ 60 YTVDARLHAV FEQSGESGKS FDYSQSLKTT TYGSSVPEQQ ITAYLSRIQR GGYIQPFGCM 120 IAVDESSFRI IGYSENAREM LGIMPQSVPT LEKPEILAMG TDVRSLFTSS SSILLERAFV 180AREITLLNPV WIHSKNTGKP FYAILHRIDV GVVIDLEPAR TEDPALSIAG AVQSQKLAVR 240 AISQLQALPG GDIKLLCDTV VESVRDLTGY DRVMVYKFHE DEHGEVVAES KRDDLEPYIG 300 LHYPATDIPQ ASRFLFKQNR VRMIVDCNAT PVLVVQDDRL TQSMCLVGST LRAPHGCHSQ 360 YMANMGSIAS LAMAVIINGN EDDGSNVASG RSSMRLWGLV VCHHTSSRCI PFPLRYACEF 420 LMQAFGLQLN MELQLALQMS EKRVLRTQTL LCDMLLRDSP AGIVTQSPSI MDLVKCDGAA 480FLYHGKYYPL GVAPSEVQIK DVVEWLLANH ADSTGLSTDS LGDAGYPGAA ALGDAVCGMA 540 VAYITKRDFL FWFRSHTAKE IKWGGAKHHP EDKDDGQRMH PRSSFQAFLE VVKSRSQPWE 600 TAEMDAIHSL QLILRDSFKE SEAAMNSKVV DGVVQPCRDM AGEQGIDELG AVAREMVRLI 660 ETATVPIFAV DAGGCINGWN AKIAELTGLS VEEAMGKSLV SDLIYKENEA TVNKLLSRAL 720 RGDEEKNVEV KLKTFSPELQ GKAVFVVVNA CSSKDYLNNI VGVCFVGQDV TSQKIVMDKF 780INIQGDYKAI VHSPNPLIPP IFAADENTCC LEWNMAMEKL TGWSRSEVIG KMIVGEVFGS 840 CCMLKGPDAL TKFMIVLHNA IGGQDTDKFP FPFFDRNGKF VQALLTANKR VSLEGKVIGA 900Nunhems Netherlands B.V. 240134WO0170 FCFLQIPSPE LQQALAVQRR QDTECFTKAK ELAYICQVIK NPLSGMRFAN SLLEATDLNE 960 DQKQLLETSV SCEKQISRIV GDMDLESIED GSFVLKREEF FLGSVINAIV SQAMFLLRDR 1020 GLQLIRDIPE EIKSIEVFGD QIRIQQLLAE FLLSIIRYAP SQEWVEIHLS QLSKQMADGF 1080 AAIRTEFRMA CPGEGLPPEL VRDMFHSSRW TSPEGLGLSV CRKILKLMNG EVQYIRESER 1140 SYFLIILELP VPRKRPLSTA SGSGDMMLMM PY 1172Non-limiting examples are described below.EXAMPLES EXAMPLE 1The lettuce M2 TILLING population (Ethyl Methane Sulfonate, EMS, induced mutations) wasscreened (summer in open field condition at Roggel, Netherlands) for delayed bolting through forward screening approach. Mutants with a significant delay in bolting (elongation of the main stem and flowering primordia) were identified through visual assessment by comparison to the corresponding non-mutated wild- type genotype. Subsequently putative M2 mutants were selfed to stabilize the background mutations and resulting M3 generations were retested to validate the delayed bolting phenotypein the summer season in the open field in Roggel (the Netherlands).For visual assessment the lettuce heads were cut open (traverse sections) to determine whether there is an elongation and differentiation of shoot apical meristem to flowering primordia.In lettuce (Lactuca sativa L.), the transition from the vegetative to reproductive stage occurs inthe meristem concealed within the rosette. During the transition, the vegetative shoot apical meristem cap is elongated, and then, the microscopic floral primordia are formed (Chen et. al.,2018, Inflorescence Development and the Role of LsFT in Regulating Bolting in Lettuce (Lactucasativa L.), Front. Plant Sci., Volume 8, Article 2248). Subsequently, rapid elongation of the steminternodes occurs, a process called bolting, and the inflorescence expands followed by flowers opening over the course of several days. Putative M2 mutants were selfed to stabilize the background mutations and resulting M3 generations were retested to validate the delayed bolting phenotype.Among the putative late / slow bolting mutants, one mutant from butter head (BTH) type of lettucewas selected (WENDEL-325-1-7) showing delay in bolting, as shown in Table A.Table A: Phenotypic differences in bolting time between the wild type WENDEL and theWENDEL-325-1-7 mutant. Wild type Mutant Difference (days) (Wendel) (WENDEL-325-1-7) Bolting time (DAS,About 45-48 About 66-69 About 21 daysdays after sowing)Nunhems Netherlands B.V. 240134WO0171 The WENDEL-325-1-7 mutant was crossed to fast bolting BTH elite lines ‘Fidel’ and ‘Maurice’ to generate two F2 populations. These two populations were subsequently phenotyped at 52 DASfor bolting time in summer in the open field in Roggel (the Netherlands) as described above. BothF2 populations exhibited a classical 3:1 phenotypic segregation pattern (Fig.1 and Fig. 2) indicating monogenic recessive inheritance of the trait. Initial QTL mapping results from the two F2 populations (n=180 per population), with genotypic data from an Infinium XT genotyping array, revealed in both populations a major QTL on chromosome 1 spanning an interval from 45Mbp to 53Mbp on the ILGC lettuce reference genome version v11. In each of the two populations, this region was further saturated with SNP markers which reduced the region to an interval of 49.6Mbp to 51.5Mbp. The field evaluation showed a difference in bolting by about three weeks. The exact timedifferences in the elongation of shoot apical meristem between the wild type and the mutant willbe compared in either an open field trial or under indoor conditions, whereby at weekly intervalsthe heads will be cut open transversely and as soon as the wild type starts bolting measurementswill be started. This way the average start of bolting can be determined in the wild types and inthe mutant, as well as the average start of flowering. EXAMPLE 2 Using whole-genome re-sequencing (WGrS) data to compare the sequences of candidate genes in the QTL interval between the WENDEL-325-1-7 EMS mutant and WENDEL wild-type fast bolting line, a G / A SNP was identified that occurred exclusively in the LSAT1V11_C10001743 gene at position chr01: 51,200,182, see Table 1 below. The mutation corresponds to a predicted pre-mature stop codon in the mutant version of this gene. This gene encodes a Phytochrome Bprotein (LsPhyB). The mutation should be present homozygously to achieve slow bolting.Thus, as mentioned above, QTL mapping and WGrS revealed a Single Nucleotide Polymorphism,SNP, at nucleotide position 51200182 of chromosome 1 of the L. sativa V11 reference genome.Table 1: EMS induced G / A SNP as shown in WGrS data from the recurrent parents of the F2mapping populations, the individual EMS mutant, a bulk of the EMS mutant and the WT Wendel line. V11 Recurrent Recurrent Mutant Mutant Wild type genome of parent Fidel parent WENDEL325- WENDEL325- WENDEL-99- lettuce line Maurice line 1-7 1-7 BULK 13 Chr.1 G / G G / G A / A A / A G / G position 51200182 (On (On (On (On (On complement complement complement complement complement strand C / C) strand C / C) strand T / T) strand T / T) strand C / C) The mutation is in the LsPhyB (phytochrome B) gene of lettuce. The G / A SNP is with reference to the V11 reference genome strand, while the LsPhyB gene is on the complement (reverse) strand and the SNP in the gene is, therefore, a C / T SNP. The wild type codon CAA (Q750) isNunhems Netherlands B.V. 240134WO0172changed into codon TAA (Stop codon) in the mutant. The mutant plant therefore has a Q750*(Q750STOP) mutation, whereby the phytochrome B protein is truncated and lacks amino acids 750 to 1125. Wild type LsPhyB protein (SEQ ID NO: 1) MASGSKASSGFHPQQVQPQNPSTSSTPRVDSMSKAIAQYAVDARLHAVYEESGESGKSFDYSHSIKTAT DSIAEQQMTAYLSKIQRGGHIQPFGCMIAIDNSSFRVIAFSENARERLGLAPQSVPSLEKTEILTIGTD VKTLFTPSSAILLERAFRAREITLLNPVWVHSKNSGKPFYAILHRIDVGIVIDLEPARTEDPALSIAGA VQSQKLAVRAISNLQALPGGDIKLLCDTVVQNVRELTGYDRVMVYKFHEDEHGEVVAECKRPDLDPYLG LHYPATDIPQASRFLFRQNRVRMIVDCHANPVPVIQDDCLMQPLCLVGSTLRAPHGCHAQYMANMGSIA SLALAVIINGNEDSGGGRGTMGLWGLVVCHHTSARCIPFPLRYACEFLMQAFGLQLNLELQLASQMLEK RILRTQTLLCDMLLRDSPTGIVTQSPSIMDLVKCDGAALFYQGKYYAAGITPTESQIKDIVEWLLACHT DSTGLSTDSLADAGYPQAASLGDVVCGMAVAYITSKDFLFWFRSHTAKEMKWGGAKHHPEDKDDGQRMH PRSSFNAFLEVVKSRSLPWENAEMDAIHSLQLILRDSFKEERDSNSKAVVKIQSEEMGLQGMDELSSVA KEMVRLIETATAPIFAVDVEGRINGWNAKIAELTGLSVSEAMGKSLVQDLIFKESQEIVIRLLHHALQG EEDKNVEIKLRTFNLSEEENAIFVVVNACCSKDYTDNIVGVCFVGQDVTRQKVVMDKFVQIQGDYRAIV HSPNPLIPPIFASDENTCCSEWNTAMEKLTGWGRDDVIGKMLVGEIFGSCCRLKGPDSLTKFMIILHNA ISGQDSDKYPFSFFDRRGKFVQALLSANKRVNLSGGDATGAFCFLQIASPELQQALKIQRQQENKCFAR MKELAYICHEIKSPLSGIRFANLLLEATDLSEDQKQLLETSAACEKQMLKIIKDVDMENIQEGHLEVEK REFVVGSVIDAVVSQVMLILRDRGVQLIRDIPEEVKTLTVCGDQTRVQQVLTNFLLNMVQHSPSPNGWV EIQVRPSLKQVFDGITNAHIEFRMVCPGNGLPAELVQDMFQSSQWSTEEGLGLSMCRKILKLMNGEVQY IRESERCYFHIVIELPLPRGT Mutant LsPhyB protein (SEQ ID NO: 2) MASGSKASSGFHPQQVQPQNPSTSSTPRVDSMSKAIAQYAVDARLHAVYEESGESGKSFDYSHSIKTAT DSIAEQQMTAYLSKIQRGGHIQPFGCMIAIDNSSFRVIAFSENARERLGLAPQSVPSLEKTEILTIGTD VKTLFTPSSAILLERAFRAREITLLNPVWVHSKNSGKPFYAILHRIDVGIVIDLEPARTEDPALSIAGA VQSQKLAVRAISNLQALPGGDIKLLCDTVVQNVRELTGYDRVMVYKFHEDEHGEVVAECKRPDLDPYLG LHYPATDIPQASRFLFRQNRVRMIVDCHANPVPVIQDDCLMQPLCLVGSTLRAPHGCHAQYMANMGSIA SLALAVIINGNEDSGGGRGTMGLWGLVVCHHTSARCIPFPLRYACEFLMQAFGLQLNLELQLASQMLEK RILRTQTLLCDMLLRDSPTGIVTQSPSIMDLVKCDGAALFYQGKYYAAGITPTESQIKDIVEWLLACHT DSTGLSTDSLADAGYPQAASLGDVVCGMAVAYITSKDFLFWFRSHTAKEMKWGGAKHHPEDKDDGQRMH PRSSFNAFLEVVKSRSLPWENAEMDAIHSLQLILRDSFKEERDSNSKAVVKIQSEEMGLQGMDELSSVA KEMVRLIETATAPIFAVDVEGRINGWNAKIAELTGLSVSEAMGKSLVQDLIFKESQEIVIRLLHHALQG EEDKNVEIKLRTFNLSEEENAIFVVVNACCSKDYTDNIVGVCFVGQDVTRQKVVMDKFV* In the NCBI database the LsPhyB wild type protein has NCBI reference number XP_023763453.1. To compare the conserved domains of the lettuce PhyB protein (LsPhyB) with the phytochrome B protein of other plants, the cucumber (CsPhyB, NCBI Reference XP_004134246.2, hereinNunhems Netherlands B.V. 240134WO0173SEQ ID NO: 8) and Arabidopsis thaliana (AtPhyB, NCBI Reference NP_179469.1, herein SEQID NO: 9) proteins were downloaded. Pairwise alignments between the wild type LsPhyB (SEQ ID NO: 1) and AtPhyB (SEQ ID NO: 9) proteins using Emboss Needle showed a sequence identity of 72.6%. Pairwise alignments between the wild type LsPhyB (SEQ ID NO: 1) and CsPhyB (SEQ ID NO: 8) proteins using Emboss Needle showed a sequence identity of 80.4%, see Figure 3. The conserved domains areindicated in Figure 3, based on the publication of Hu et al. 2023, Theoretical Applied Genetics136: 68. EXAMPLE 3To further analyze the phenotype of the lettuce Q750* mutant under different light conditionsexperiments under indoor controlled conditions were set up, using normal lighting (white light, ~150µmol / m2 / s, with a ratio of Red:FarRed, R:FR, of 1.0) and light stress (white light 150µmol / m2 / splus Far Red light, with a ratio of Red:FarRed, R:FR, of 0.4) conditions, as well as various seedlingdensities (D1 = 100 plants per square meter, D2 = 200 plants per square meter and D3 = 400 plants per square meter). Seedling densities of 400 plants per square meter are extremely high densities.Initial phenotyping at 30 DAS (week 4, W4) and 37 DAS (week 5, W5) was done.Results were as follows. Plant height and plant weight at 30 DAS and 37 DAS Plant height is the length from the cotyledons to the tip of the longest leaf (measured in cm). Plant weight is the total weight per plant. Only data for 37 DAS is shown as the data for 30 DAS are similar. Several plants per genotype were measured and the average value is provided. Treatment Plant height (cm) of Plant height (cm) of wild type mutant at 37 DAS at 37 DAS (light treatment and seedling density: (WENDEL325-1-7, (WENDEL-99) D1 = 100 seedlings / m2, comprising Q750* homozygous) D2 = 200 seedlings / m2, D3 = 400 seedlings / m2) White light - D1 17.7 18.9White light - D2 20.9 21.1White light - D3 20.2 22.2Mean White Light 19.6 20.7White light +FR (R:FR = 0.4) - D1 17.6 19.2Nunhems Netherlands B.V. 240134WO0174 White light +FR (R:FR = 0.4) - D2 20.6 (Figure 4, right side) 24.0 (Figure 4, left side)White light +FR (R:FR = 0.4) - D3 19.9 (Figure 5, right side) 24.6 (Figure 5, left side)Mean White light + FR (ratio 19.3 22.6Red:FarRed = 0.4) Mean D1 17.6 19.1Mean D2 20.7 22.6Mean D3 20.0 23.4Mean mutant vs wild type 19.5 21.7*FR = Far RedAs can be seen from the data and in Figures 4 and 5 (taken at 35 DAS), there is a difference inplant height between the mutant and the wild type under light stress conditions and high density of seedlings. The wild type shows extension of the internodes and the plants are higher underthese stress conditions compared to the mutant. The wild type plants, thus, show a typical shadeavoidance reaction (also referred to as shade avoidance syndrome, SAS), while the mutant does not. Plant weight is the weight of the total plant (grams). Several plants per genotype were measuredand the average value is provided. Only data for 37 DAS is shown as the data for 30 DAS aresimilar. Treatment Plant weight (grams) of Plant weight (grams) of wild Mutant at 37 DAS type at 37 DAS (light treatment and seedling density: (WENDEL325-1-7, (WENDEL-99) D1 = 100 seedlings / m2, comprising Q750* homozygous) D2 = 200 seedlings / m2, D3 = 400 seedlings / m2) White light - D1 25.0 29.1White light - D2 20.1 22.7White light - D3 12.8 18.3Mean White Light 19.3 23.4White light +FR (R:FR = 0.4) - D1 27.1 30.0White light +FR (R:FR = 0.4) - D2 19.2 26.6Nunhems Netherlands B.V. 240134WO0175 White light +FR (R:FR = 0.4) - D3 16.3 19.2Mean White light + FR (ratio 20.9 25.3Red:FarRed = 0.4) Mean D1 26.0 29.5Mean D2 19.6 24.7Mean D3 14.5 18.8Mean mutant vs wild type 20.1 26.6*FR = Far RedAs can be seen from the data, there is a difference in plant weight between the mutant and thewild type, with the mutant plant weight being somewhat less than the wild type plant weight. This is largely due to a thinner stem being present in the mutant and due to the differences in plant height (see table further above). Internodal length index The index of plant height (mm) / number of fully opened leaves gives an indication of mean internodal length, referred to as mean internodal length index. Treatment Mean internodal length Mean internodal length index index of mutant of wild type (light treatment and seedling density: (WENDEL325-1-7, (WENDEL-99) D1 = 100 seedlings / m2, comprising Q750* homozygous) D2 = 200 seedlings / m2, D3 = 400 seedlings / m2) White light - D1 10.6 11.0White light - D2 15.2 16.3White light - D3 18.8 17.4Mean White Light 14.2 14.5White light +FR (R:FR = 0.4) - D1 11.9 13.2White light +FR (R:FR = 0.4) - D2 15.8 17.1White light +FR (R:FR = 0.4) - D3 16.2 18.9Nunhems Netherlands B.V. 240134WO0176 Mean White light + FR (ratioRed:FarRed = 0.4) 14.5 16.3Mean D1 11.2 12.0Mean D2 15.5 16.7Mean D3 17.4 18.2Mean mutant vs wild type 14.4 15.4*FR = Far Red As can be seen above the wild type plant responds to stress conditions (R:FR = 0.4 and increased plant density) by elongation of the internodes, while the mutant plant does not show internode elongation in response to stress conditions. See also Figures 4 and 5 showing internode elongation of the wild type plants (left side). Leaf length and leaf width at 30 DAS Leaf length and leaf width were measured at 30 DAS for the mutant and the wild type seedlings.Again measurements were done for several seedlings per genotype and the average values areshown. Treatment Leaf length Leaf length (cm) of Leaf width (cm) Leaf width (cm) (cm) of Mutant wild type at 30 of Mutant at 30 of wild type at (light treatment and at 30 DAS DAS DAS 30 DAS seedling density: (WENDEL325- (WENDEL-99) (WENDEL325- (WENDEL-99) D1 = 100 1-7, 1-7, comprising seedlings / m2, comprising Q750* Q750* homozygous) D2 = 200 homozygous) seedlings / m2, D3 = 400 seedlings / m2) White light - D1 14.9 14.8 8.6 9.4White light - D2 16.5 19.1 8.0 7.9White light - D3 16.2 16.2 7.9 7.5Mean White Light 15.8 16.7 8.2 8.3White light +FR (R:FR =0.4) - D1 15.0 15.0 9.9 9.2Nunhems Netherlands B.V. 240134WO0177 White light +FR (R:FR =0.4) - D2 15.2 18.2 9.3 9.6White light +FR (R:FR =0.4) - D3 17.0 17.8 9.8 8.5Mean White light + FR (ratio Red:FarRed= 0.4) 15.7 17.0 9.7 9.1Mean D1 14.9 14.9 9.3 9.3Mean D2 15.8 18.6 8.7 8.8Mean D3 16.6 17.0 8.8 8.0Mean mutant vs wild type 15.8 16.8 8.9 8.7*FR = Far RedFor leaf width no differences were found between the mutant and the wild type under any of theconditions. For leaf length the mutant had slightly shorter leaves under stress conditions (light stress and density stress) compared to the wild type. Number of leaves at 30 DAS and 37 DAS No significant difference was found between the number of leaves (full open leaves counted) between the mutant and the wild type at 30 DAS and at 37 DAS under any of the conditions. Data not shown. EXAMPLE 4 Targeted mutagenesis Target-specific genome editing using engineered nucleases has become widespread in various fields. Single-base substitutions can be performed by homologous recombination (HR). Calli from plants can be mutagenized by co-transformation with a plasmid and e.g. donor fragment throughparticle bombardment, as described in e.g. Okamoto et al. (2019) Scientific Reports 9:4811. Suchplasmid would harbour cassettes expressing e.g. CAS9 and two guideRNAs (gRNAs) and e.g. a donor fragment as template for homology-directed repair (HDR). Expression of the Cas9 gene and gRNA are driven by a strong promoter such as a ubiquitin promoter. The gRNAs are be designed at complementary strands of the of the two targeting sites.The donor fragment contains the desired mutation e.g. in the middle of a fragment of, for example,476 bp that corresponds to the sequence of the target gene (except for the mutation). Optionally, additional synonymous mutations, that do not change amino acid residues in the donor fragment, would prevent Cas9 from cutting the donor fragment again, once HDR is successfully achieved.The fragment is flanked with two gRNA target sequences including the PAM motifs, respectively,Nunhems Netherlands B.V. 240134WO0178 so that the donor DNA can be released by Cas9 / gRNAs from the plasmid; see e.g. Sun et al. (2016) Molecular Plant 9, 628–631 DOI: 10.1016 / j.molp.2016.01.001. To increase HDR, additional free DNA donor fragment can be co-introduced in the plant calli by particle bombardment. After calli bombardment, regenerated shoots selected based on plasmid encoded antibiotics resistance, are grown and analysed for the presence of mutations. This could be done by primers to amplify a target gene sequence from DNA by PCR. Primer are designed so that they cannot amplify a fragment from the plasmid. The amplified product can be sequenced to validate the presence of the mutation. Plants can be regenerated from plant material comprising the desired mutation, such as calli orcultured plant cells, using standard methods.Obviously other targeted gene editing systems may be used, e.g. Cas12 (or a subtype of Cas12,such as Cas12a) or other systems. Alternatively base editing or prime editing systems may beused, see e.g. review Molla et al. 2021, Nature Plants, VOL 7, p 1166–1187).EXAMPLE 5An indoor controlled environment experiment was carried out in Haelen (the Netherlands) toassess the response of hypocotyl length of the LsPhyB mutant (WENDEL-325-1-7) mutantcomprising the Q750* mutant allele. A shade-stress-inducing environmental condition wassimulated through far-red light enrichment (white light + FR <~150 µmol / m2 / s>, with R / FR = 0.4).As a control condition regular light (white light <~150 µmol / m2 / s>, with R / FR = 1.0) was used.Planting density was 200 plants per m2 in both shade stress and control treatment.The following table shows a comparison of the average hypocotyl lengths (mm) of the mutant and wild type seedlings under control conditions and shade stress-inducing conditions 8 days after sowing: Treatments Wild type - average hypocotyl Mutant - average hypocotyllength (mm) length (mm) White Light condition21.4 32.8(control) Shade stress condition 27.6 27.4Difference between shade6.2 - 5.4stress vs control See also Figure 6.Nunhems Netherlands B.V. 240134WO0179 The hypocotyl of the wild type seedlings responded to the shade stress conditions by elongation, while the hypocotyl of the LsPhyB mutant (WENDEL-325-1-7) was elongated both under whitelight conditions and shade stress conditions, which is in agreement with observations of PhyBmutants described in cucumber (Hu et al.2023, supra). EXAMPLE 6A lettuce TILLING populations (see also Example 1), background Wendel, was screened forplants comprising mutations in the LsPhyB gene.A large number of plants comprising mutant phyB alleles were identified, with in total 4 plantscomprising mutant alleles encoding truncated proteins due to a premature stop codon and 183 plants comprising mutant alleles wherein a single amino acid is substituted by a different amino acid. Line Mutation Amino acid change in theProtein domain containing wild type PhyB protein of the amino acid change SEQ ID NO: 1 WENDEL_M-1839H1 C / T Q91Stop N-terminal regionWENDEL_M-1597H1 G / A W369Stop GAF-domainWENDEL_M-4H1 G / A W524Stop Phy-domainWENDEL_M-207H1 G / T E707Stop Pas1-domainPlants homozygous for the mutant alleles will be analyzed for their phenotype compared to controlplants which comprise the wild type LsPhyB allele in homozygous form and optionally comparedto the Q750* mutant described in the preceding examples above. Especially delayed bolting willbe analyzed. EXAMPLE 7 TILLING mutants homozygous for the mutant allele were analyzed by growing plants in peat soilin pots in the greenhouse together with suitable controls comprising the wild type LsPhyB allele.At 65 days after sowing the bolting phenotype was assessed visually. At this time the controls showed a bolting phenotype. Line Amino acidProtein domain Bolting phenotype change in the containing theat 65 days ofwild type PhyB amino acid change homozygous protein of SEQ mutant plant ID NO: 1 WENDEL_M-1839H1 Q91Stop N-terminal region No bolting signsNunhems Netherlands B.V. 240134WO0180 WENDEL_M-1597H1 W369Stop GAF-domain No bolting signsWENDEL_M-4H1 W524Stop Phy-domain No bolting signsModulator loop No bolting signs WENDEL_325 Q750StopdomainThe four mutants which encoded truncated lsphyb proteins had a significant delay in boltingcompared to the wild type controls. At 65 days after sowing the controls showed a bolting phenotype, while the plants homozygous for the mutant alleles were in vegetative state and nosigns of bolting were seen. These data confirm that a loss-of-function of LsPhyB results in a delayin bolting in lettuce.

Claims

Nunhems Netherlands B.V. 240134WO0181 CLAIMS1. A Lactuca sativa plant or plant part or seed comprising in its genome at least one copy of amutant allele of the Phytochrome B (LsPhyB) gene, wherein the mutant allele encodes amutant protein comprising a deletion, truncation, insertion and / or replacement of one or more amino acids compared to the wild type LsPhyB protein encoded by the wild type allele, resulting in a loss-of-function of the mutant protein, wherein the mutant allele confers delayed bolting when the mutant allele is present in homozygous form compared to the control plant lacking the mutant allele, wherein the wild type LsPhyB protein of the wild type allele is encoded by nucleic acid molecules selected from the group consisting of: a) nucleic acid molecules, which encode a protein with the amino acid sequence given under SEQ ID NO: 1;b) nucleic acid molecules, which encode a protein, the sequence of which has an identity of at least 95%, 96%, 97%, 98% or 99% with the amino acid sequence given under SEQ IDNO: 1;c) nucleic acid molecules, which comprise the nucleotide sequence shown under SEQ ID NO: 5 or a complimentary sequence thereof;d) nucleic acid molecules, which have an identity of at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% with the nucleic acid sequences described under c);e) nucleic acid molecules, which hybridize with at least one strand of the nucleic acid molecules described under a), b), c), or d) under stringent conditions of at least one wash in 0.2X SSC at a temperature of at least 50°C for 20 min; and f) nucleic acid molecules, the nucleotide sequence of which deviates from the sequence of the nucleic acid molecules identified under a) or b) due to the degeneration of the genetic code.

2. The Lactuca sativa plant or plant part or seed according to claim 1, wherein said plant is ahorticultural type selected from a butterhead lettuce type and a loose leaf type, such as amulti-leaf lettuce type.

3. The Lactuca sativa plant according to claim 1 or 2, wherein in the mutant allele a codon inthe Modulator Loop domain or preceding the Modulator loop domain, or a codon in the PAS2-domain or preceding the PAS2-domain is replaced by a premature STOP codon, whereby the protein is truncated as of the premature STOP codon.

4. The Lactuca sativa plant according to any one of claims 1 to 3, wherein in the mutant allelethe codon for Glutamine (Q, Gln) at position 750 of SEQ ID NO: 1, or the codon for aGlutamine (Q, Gln) at position 91 of SEQ ID NO: 1, or the codon for a Tryptophan (W, Trp)at position 369 of SEQ ID NO: 1, or the codon for a Tryptophan (W, Trp) at position 524 of SEQ ID NO: 1, or at the equivalent amino acid in a sequence comprising at least 95%sequence identity to SEQ ID NO: 1, is replaced by a STOP codon.Nunhems Netherlands B.V. 240134WO01825. The Lactuca sativa plant according to any one of claims 1 to 4, wherein the Lactuca sativaplant is homozygous for the mutant allele.

6. The Lactuca sativa plant according to any one of claims 1 to 5, wherein the Lactuca sativaplant is an inbred plant, a dihaploid plant or a hybrid plant.

7. The Lactuca sativa plant according to any one of claims 1 to 6, wherein the Lactuca sativaplant is of the head lettuce type or of the teen-leaf or baby-leaf type.

8. A seed from which the Lactuca sativa plant according to any one of claims 1 to 7 can begrown.

9. A plant cell, tissue or plant part of the Lactuca sativa plant according to any one of claims 1to 7 or of the seed according to claim 8, comprising the mutant allele as defined in anyone of claims 1 to 4.

10. A method for producing harvested lettuce plant material, said method comprising growing aLactuca sativa plant according to any one of claims 5 to 8 and harvesting plant materialproduced by said Lactuca sativa plant.

11. The method according to claim 10, wherein said lettuce plants are grown under conditions where a plant comprising the wild type LsPhyB allele in homozygous form shows shadeavoidance symptoms, such as an increase in internode length and / or an increase in plant height.

12. The method according to claim 11, wherein said conditions are seedling densities of at least 200 plants / m2 and / or a Red to FarRed (R:FR) light ratio of 0.6, 0.5, 0.4 or less.

13. A method for identifying and / or selecting a Lactuca sativa plant or plant part or seed comprising in its genome at least one copy of a mutant allele of the Phytochrome B (LsPhyB) gene, wherein the mutant allele encodes a loss-of-function protein, said method comprising analysing whether the genomic DNA of said Lactuca sativa plant or plant part comprises the mutant allele.

14. The method according to claim 13, wherein the mutant allele encodes a mutant proteinwherein a codon in the Modulator Loop domain or preceding the Modulator loop domain, or a codon in the PAS2-domain or preceding the PAS2-domain is replaced by a premature STOP codon, whereby the protein is truncated as of the premature STOP codon, said method comprising analysing whether the genomic DNA of said Lactuca sativa plant or plant part comprises the mutant allele.

15. The method according to claim 13 or 14 wherein the mutant allele encodes a truncatedprotein wherein the codon for the Glutamine at amino acid 750 of SEQ ID NO: 1 (aminoacid Q750), or the codon for a Glutamine (Q, Gln) at position 91 of SEQ ID NO: 1, or thecodon for a Tryptophan (W, Trp) at position 369 of SEQ ID NO: 1, or the codon for a Tryptophan (W, Trp) at position 524 of SEQ ID NO: 1, or the equivalent amino acid in aNunhems Netherlands B.V. 240134WO0183 wild type LsPhyB protein comprising at least 95% sequence identity to SEQ ID NO: 1, ischanged into a stop codon.

16. The method according to any one of claims 13 to 15, comprising carrying out a methodselected from: a PCR - assay, a SNP-genotyping assay such as a KASP-assay or aTaqMan-assay, a High Resolution Melting (HRM) assay, or DNA sequencing.

17. The method according to any one of claims 13 to 15, wherein the Lactuca sativa plant orplant part is subjected to a mutation inducing step prior to determining whether the Lactuca sativa plant or plant part comprises a mutant allele of the LsPhyB gene.

18. The method according to claim 17, wherein the mutation inducing step compriseschemical mutagenesis, preferably using ethyl methanesulfonate (EMS) as mutagenic agent.

19. A method for producing a Lactuca sativa plant comprising a mutant allele which delaysbolting of said plant when present in homozygous form, said method comprising thestep(s) of: (i) crossing a first Lactuca sativa plant and a second Lactuca sativa plant, whereinthe first Lactuca sativa plant comprises in its genome at least one copy of a mutantallele according to any one of claims 1 to 4, (ii) optionally harvesting seed from the crossing of (i) and(iii) optionally selecting seed comprising said mutant allele in its genome.

20. The method according to any one of claims 10 to 12, wherein said lettuce plants are grownin a hydroponic system.

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