Modulation of alkaloid levels in tobacco via mutation of quinolinate synthase

Abstract

There is disclosed a Nicotiana tabacum plant or part thereof comprising: (a) a mutated polynucleotide sequence encoding a Nicotiana tabacum quinolinate synthase (NtQS-T) polypeptide comprising a contiguous polypeptide sequence of SEQ ID NO: 3 and comprising at least one mutation therein that modulates alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant; (b) a mutated polypeptide sequence encoded by the polynucleotide sequence set forth in (a); or (c) a construct, vector or expression vector comprising the mutated polynucleotide sequence set forth in (a), wherein the cysteine at amino acid position 133 of NtQS-T is substituted in the mutated polypeptide.

Description

[0001] MODULATION OF ALKALOID LEVELS IN TOBACCO VIA MUTATION OF QUINOLINATE SYNTHASE FIELD OF THE INVENTION The present invention relates to Nicotiana tabacum plants having modulated (for example, decreased) (total) alkaloid levels by mutating quinolinate synthase (QS). TSNA levels can also be modulated (for example, decreased). Plant material from the plants, products containing the plant material and methods are also described. BACKGROUND Certain plants - such as tobacco plants - accumulate high levels of free nitrate in their leaves, which is undesirable because high levels of nitrate have been associated with the formation of carcinogenic compounds referred to as tobacco-specific nitrosamines (TSNAs). TSNAs are a class of compounds that are predominantly produced during the curing of tobacco leaves, though additional formation can occur in the subsequent processing and storage of leaf, and possibly via pyrosynthesis during combustion. Two of the TSNAs found in the cured leaf, N-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-l-(3-pyridyl)-l - butanone (NNK), are classified as Group I carcinogens (the highest designation) by the International Agency for Research on Cancer. Due to the volume of evidence implicating these compounds with various tobacco-associated cancers, the World Health organization has recommended that mandates be implemented to ensure that future tobacco products have reduced levels of these toxicants. TSNAs represent nitrosation products of tobacco alkaloids. In air-cured tobaccos, there is a general consensus that nitrite is the agent directly responsible for TSNA formation. Due to its cellular toxicity, however, endogenous nitrite levels are typically very low in plant tissues. Instead, it is believed that the great majority of the nitrite involved in TSNA formation is derived from the nitrate reductase activity of microbes residing on the leaf surface during the 6-10 week curing process that converts a portion of the leaf nitrate pools to nitrite as cellular membranes and organelles become degraded during this period. TSNAs are formed primarily during the curing process of leaves and involve the nitrosation of tobacco alkaloids. Genetic strategies to lower TSNA content and levels in cured leaf have focused on targeting either: (1) the alkaloid precursor(s); or (2) the nitrosating agent(s) involved. Most efforts to reduce TSNAs at the level of altering the genetics of tobacco have targeted the alkaloid precursors to TSNAs. Such strategies provide substantial reductions in NNN through the downregulation of the gene family responsible for the synthesis of its alkaloid precursor nomicotine. Modified tobacco plants having reduced nitrate levels are described by the present applicant in WO2016 / 046288. As described therein, the expression or activity of a nitrate reductase enzyme is deregulated. Overexpression of the mutant nitrate reductase enzyme gave a dramatic increase in nitrate assimilation, resulting in low nitrate / TSNA content and higher amino acid levels. Plants displayed 90% less nitrate compared to the control. Another way to reduce TSNAs in tobacco products is by lowering alkaloids levels. Different alkaloids naturally occurring in tobacco leaves nitrosate to different TSNAs. It can be desirable to develop non-genetically modified organism (non-GMO) approaches to reduce nitrate accumulation. Due to the difficulties of growing and commercialising genetically modified crops in countries, including Europe, it can be advantageous to work with mutants featuring single nucleotide polymorphisms rather than mutants obtained through the use of genetic engineering techniques. There remains a continuing need in the art for reducing TSNAs is tobacco plants, especially via non-transgenic approaches. SUMMARY OF THE INVENTION The present inventors have identified two genes (NtQS-S and NtQS-T), belonging to the QS enzyme family. The present invention is based, at least in part, on the finding that mutating Nicotiana tabacum QS can result in plants or plant material in which the (dried or cured) leaves thereof contain modulated (for example, decreased or reduced) levels of (total) alkaloid as compared to (dried or cured) leaves derived from a control plant. TSNA levels – such as N'-nitrosoanabasine (NAB), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N′-nitrosoanatabine (NAT) and N-Nitrosonornicotine (NNN) levels - can also be modulated (for example, decreased). One such mutation that is described herein is C133Y in NtQS-T – meaning that cysteine at amino acid position 133 of NtQS-T is substituted for tyrosine. Advantageously, dried or cured leaves containing this C133Y mutation have lower levels of (total) alkaloid as compared to dried or cured leaves of their outsegregant wild types. More specifically, a statistically significant decrease of nicotine, nornicotine, anatabine and myosmine is observed in the mutant. Anabasine levels are also impaired in the mutant. Advantageously, the dried or cured leaves containing this C133Y mutation in NtQS-T can also have lower levels of TSNAs – such as N'-nitrosoanabasine (NAB), 4- (methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N′-nitrosoanatabine (NAT) and N- Nitrosonornicotine (NNN) - as compared to dried or cured leaves of their outsegregant wild types. These results are surprising because the results observed herein are different to those results obtained in previously reported work on QS. US2016 / 0010103 describes a correlation between only a low anatabine trait and QS in tobacco. Without being bound by any particular theory, it is believed that the mutation in NtQS-T reduces the expression of NtQS-T or reduces the function or activity of NtQS-T, which causes a decrease in the level of (total) alkaloid and TSNAs – such as NAB, NNK, NAT and NNN and optionally nitrate. Producing plants according to the present disclosure provides a number of other advantages. For example, the plants described herein can, in certain embodiments, be non-genetically modified plants which overcomes the difficulties of growing and commercialising genetically modified crops. In a first aspect, there is disclosed a Nicotiana tabacum plant or part thereof comprising: (a) a mutated polynucleotide sequence encoding a Nicotiana tabacum quinolinate synthase (NtQS-T) polypeptide comprising a contiguous polypeptide sequence of SEQ ID NO: 3 and comprising at least one mutation therein that modulates (total) alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant; (b) a mutated polypeptide sequence encoded by the polynucleotide sequence set forth in (a); or (c) a construct, vector or expression vector comprising the mutated polynucleotide sequence set forth in (a), wherein the cysteine at amino acid position 133 of NtQS-T is substituted in the mutated polypeptide. In a second aspect, there is disclosed Nicotiana tabacum cured or dried plant material (for example, cured or dried leaf) comprising: (a) a mutated polynucleotide sequence encoding a Nicotiana tabacum quinolinate synthase (NtQS-T) polypeptide comprising a contiguous polypeptide sequence of SEQ ID NO: 3 and comprising at least one mutation therein that modulates (total) alkaloid levels in cured or dried plant material (for example, cured or dried leaf) as compared to control cured or dried plant material (for example, control cured or dried leaf); (b) a mutated polypeptide sequence encoded by the polynucleotide sequence set forth in (a); or (c) a construct, vector or expression vector comprising the mutated polynucleotide sequence set forth in (a), wherein the cysteine at amino acid position 133 of NtQS-T is substituted in the mutated polypeptide. Suitably, the cysteine at amino acid position 133 of NtQS-T is substituted for an aromatic amino acid selected from the group consisting of histidine, phenylalaine, tryptophan, asparagine and tyrosine. Suitably, the cysteine at amino acid position 133 of NtQS-T is substituted for tyrosine (C133Y) in the mutated polypeptide. Suitably, the mutated polypeptide comprises the contiguous polypeptide sequence of SEQ ID NO: 5. Suitably, the mutated polypeptide consists of the contiguous polypeptide sequence of SEQ ID NO: 5 Suitably, the mutated polynucleotide sequence comprises, consists or consists essentially of the polynucleotide sequence set forth in SEQ ID NO: 4. Suitably, the alkaloids are nicotine, nornicotine, anatabine and myosmine or total alkaloid. Suitably, the alkaloids are nicotine, nornicotine, anatabine, myosmine and anabasine. Suitably, at least one mutation reduces (total) alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant. In a third aspect, there is disclosed Nicotiana tabacum plant material, cured plant material, or homogenized plant material obtained from the Nicotiana tabacum plant or part thereof according to the first aspect of the present invention. In a fourth aspect, there is disclosed a method for preparing a Nicotiana tabacum plant or part thereof having modulated (total) alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant comprising: (a) providing a Nicotiana tabacum plant; (b) introducing into the Nicotiana tabacum plant one or more mutations in a quinolinate synthase (NtQS-T) polypeptide comprising or consisting of a contiguous polypeptide sequence of SEQ ID NO: 3; (c) determining if the one or more mutations modulate (total) alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant; and (d) identifying a Nicotiana tabacum plant or part thereof comprising one or more mutations in NtQS-T that modulate (total) alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant. In a fifth aspect, there is disclosed a method for producing cured Nicotiana tabacum plant material with an altered amount of (total) alkaloid as compared to control plant material, comprising: (a) providing the Nicotiana tabacum plant or part thereof according to the first aspect of the present invention or the plant material according to the third aspect of the present invention; (b) harvesting the Nicotiana tabacum plant or part thereof or Nicotiana tabacum plant material; and (c) curing the harvested Nicotiana tabacum plant or the harvested Nicotiana tabacum plant material. Suitably, the plant material is leaf and the curing method is selected from the group consisting of air curing, fire curing, smoke curing, and flue curing. In a sixth aspect, there is disclosed a cured or dried leaf obtained from the Nicotiana tabacum plant or part thereof according to the first aspect of the present invention or Nicotiana tabacum cured or dried plant material according to the second aspect of the present invention or obtained by the method according to the fourth and fifth aspects of the present invention Suitably, the leaves are air-cured or sun-cured or flue-cured or fermented. In a seventh aspect, there is disclosed a tobacco product comprising the Nicotiana tabacum plant or part thereof according to the first aspect of the present invention or the Nicotiana tabacum cured or dried plant material according to the second aspect of the present invention or the plant material according to the third aspect of the present invention or the cured or dried leaf according to the sixth aspect of the present invention. Suitably, the at least one mutation modulates TSNA levels – such as levels of N'- nitrosoanabasine (NAB), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N′- nitrosoanatabine (NAT) and N-Nitrosonornicotine (NNN) levels - in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from the control plant. DEFINITIONS Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present invention. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting. The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “and” and “the” include plural references unless the context clearly dictates otherwise. The term “and / or” means (a) or (b) or both (a) and (b). The present disclosure contemplates other embodiments “comprising,” “consisting of” and “consisting essentially of” the embodiments or elements presented herein, whether explicitly set forth or not. For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the numbers 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 and 7.0 are explicitly contemplated. As used throughout the specification and the claims, the following terms have the following meanings: “Coding sequence” or “polynucleotide encoding” means the nucleotides (RNA or DNA molecule) that comprise a polynucleotide which encodes a polypeptide. The coding sequence can further include initiation and termination signals operably linked to regulatory elements including a promoter and polyadenylation signal capable of directing expression in the cells of an individual or mammal to which the polynucleotide is administered. The coding sequence may be codon optimized. “Complement” or “complementary” can mean Watson-Crick (for example, A-T / U and C-G) or Hoogsteen base pairing between nucleotides or nucleotide analogs. “Complementarity” refers to a property shared between two polynucleotides, such that when they are aligned antiparallel to each other, the nucleotide bases at each position will be complementary. "Construct" refers to a double-stranded, recombinant polynucleotide fragment comprising one or more polynucleotides. The construct comprises a "template strand" base-paired with a complementary "sense or coding strand." A given construct can be inserted into a vector in two possible orientations, either in the same (or sense) orientation or in the reverse (or anti- sense) orientation with respect to the orientation of a promoter positioned within a vector - such as an expression vector. The term "control" in the context of a control plant or a control plant cell means a plant or plant cell containing the wild type NtQS-T gene or polypeptide as set forth in SEQ ID NOs: 3 and 4, respectively, and so it can provide a comparison with a plant containing a mutation therein that modulates (for example, reduces) the levels of (total) alkaloids, TSNAs - such as NNK, NNN, NAB and NAT – and optionally nitrate therein. As used herein, a “control plant” is a plant that is substantially equivalent to a test plant or modified plant in all parameters with the exception of the test parameters. For example, when referring to a plant into which a mutation has been introduced, a control plant is an equivalent plant into which the mutation has not been introduced. The control plant can be an outsegregant control plant. "Expression" refers to the production of a functional product. For example, expression of a polynucleotide fragment may refer to transcription of the polynucleotide fragment (for example, transcription resulting in mRNA or functional RNA) and / or translation of mRNA into a precursor or mature polypeptide. “Functional” and “full-functional” describes a polypeptide that has biological function or activity. A “functional gene” refers to a gene transcribed to mRNA, which is translated to a functional or active polypeptide. “Genetic construct" refers to DNA or RNA molecules that comprise a polynucleotide that encodes a polypeptide. The coding sequence can include initiation and termination signals operably linked to regulatory elements including a promoter and polyadenylation signal capable of directing expression. The terms "homology” or “similarity" refer to the degree of sequence similarity between two polypeptides or between two polynucleotide molecules compared by sequence alignment. The degree of homology between two discrete polynucleotides being compared is a function of the number of identical, or matching, nucleotides at comparable positions. "Identical" or "identity" in the context of two or more polynucleotides or polypeptides means that the sequences have a specified percentage of residues that are the same over a specified region. The percentage may be calculated by optimally aligning the two sequences, comparing the two sequences over the specified region, determining the number of positions at which the identical residue occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the specified region, and multiplying the result by 100 to yield the percentage of sequence identity. In cases where the two sequences are of different lengths or the alignment produces one or more staggered ends and the specified region of comparison includes only a single sequence, the residues of single sequence are included in the denominator but not the numerator of the calculation. When comparing DNA and RNA, thymine (T) and uracil (U) may be considered equivalent. Identity may be determined manually or by using a computer sequence algorithm such as ClustalW, ClustalX, BLAST, FASTA or Smith-Waterman. The popular multiple alignment program ClustalW (Nucleic Acids Research (1994) 22, 4673- 4680; Nucleic Acids Research (1997), 24, 4876-4882) is a suitable way for generating multiple alignments of polypeptides or polynucleotides. Suitable parameters for ClustalW maybe as follows: For polynucleotide alignments: Gap Open Penalty = 15.0, Gap Extension Penalty = 6.66, and Matrix = Identity. For polypeptide alignments: Gap Open Penalty = 10. o, Gap Extension Penalty = 0.2, and Matrix = Gonnet. For DNA and Protein alignments: ENDGAP = -1, and GAPDIST = 4. Those skilled in the art will be aware that it may be necessary to vary these and other parameters for optimal sequence alignment. Suitably, calculation of percentage identities is then calculated from such an alignment as (N / T), where N is the number of positions at which the sequences share an identical residue, and T is the total number of positions compared including gaps but excluding overhangs. The terms "isolated" or "purified" refer to material that is substantially or essentially free from components that normally accompany it as found in its native state. Purity and homogeneity are typically determined using analytical chemistry techniques such as polyacrylamide gel electrophoresis or high performance liquid chromatography. A polypeptide that is the predominant species present in a preparation is substantially purified. In particular, an isolated polynucleotide is separated from open reading frames that flank the desired gene and encode polypeptides other than the desired polypeptide. The term "purified" as used herein denotes that a polynucleotide or polypeptide gives rise to essentially one band in an electrophoretic gel. Particularly, it means that the polynucleotide or polypeptide is at least 85% pure, more suitably at least 95% pure, and most suitably at least 99% pure. Isolated polynucleotides may be purified from a host cell in which they naturally occur. Conventional polynucleotide purification methods known to skilled artisans may be used to obtain isolated polynucleotides. The term also embraces recombinant polynucleotides and chemically synthesized polynucleotides. "Modulate" or “modulating” refers to causing or facilitating a qualitative or quantitative change, alteration, or modification in a process, pathway, function or activity of interest. Without limitation, such a change, alteration, or modification may be an increase or decrease in the relative process, pathway, function or activity of interest. For example, gene expression or polypeptide expression or polypeptide function or activity can be modulated. For example, levels of (total) alkaloids and optionally nitrate can be modulated. Levels of TSNAs – such as NAB, NNK, NAT and NNN can also be modulated. Typically, the relative change, alteration, or modification will be determined by comparison to a control. The term 'non-naturally occurring' describes an entity – such as a polynucleotide, a genetic mutation, a polypeptide, a plant, a plant cell and plant material - that is not formed by nature or that does not exist in nature. Such non-naturally occurring entities or artificial entities may be made, synthesized, initiated, modified, intervened, or manipulated by methods described herein or that are known in the art. Such non-naturally occurring entities or artificial entities may be made, synthesized, initiated, modified, intervened, or manipulated by man. By way of example, a non-naturally occurring entity can be an entity that has been mutated by methods known to induce mutagenesis, including site-directed mutagenesis, oligonucleotide- directed mutagenesis, chemically-induced mutagenesis, irradiation-induced mutagenesis, mutagenesis utilizing modified bases, mutagenesis utilizing gapped duplex DNA, double- strand break mutagenesis, mutagenesis utilizing repair-deficient host strains, mutagenesis by total gene synthesis, DNA shuffling and other equivalent methods. For example, chemical mutagenesis can be used which involves the use of exogenously added chemicals – such as mutagenic, teratogenic, or carcinogenic organic compounds – to induce mutations. Mutants with advantageous properties can then be selected and identified. “Oligonucleotide” or “polynucleotide” means at least two nucleotides covalently linked together. The depiction of a single strand also defines the sequence of the complementary strand. Thus, a polynucleotide also encompasses the complementary strand of a depicted single strand. Many variants of a polynucleotide may be used for the same purpose as a given polynucleotide. Thus, a polynucleotide also encompasses substantially identical polynucleotides and complements thereof. A single strand provides a probe that may hybridize to a given sequence under stringent hybridization conditions. Thus, a polynucleotide also encompasses a probe that hybridizes under stringent hybridization conditions. Polynucleotides may be single stranded or double stranded, or may contain portions of both double stranded and single stranded sequence. The polynucleotide may be DNA, both genomic and cDNA, RNA, or a hybrid, where the polynucleotide may contain combinations of deoxyribo- and ribo-nucleotides, and combinations of bases including uracil, adenine, thymine, cytosine, guanine, inosine, xanthine hypoxanthine, isocytosine and isoguanine. Polynucleotides may be obtained by chemical synthesis methods or by recombinant methods. The specificity of single-stranded DNA to hybridize complementary fragments is determined by the "stringency" of the reaction conditions (Sambrook et al., Molecular Cloning and Laboratory Manual, Second Ed., Cold Spring Harbor (1989)). Hybridization stringency increases as the propensity to form DNA duplexes decreases. In polynucleotide hybridization reactions, the stringency can be chosen to favor specific hybridizations (high stringency), which can be used to identify, for example, full-length clones from a library. Less-specific hybridizations (low stringency) can be used to identify related, but not exact (homologous, but not identical), DNA molecules or segments. DNA duplexes are stabilised by: (1) the number of complementary base pairs; (2) the type of base pairs; (3) salt concentration (ionic strength) of the reaction mixture; (4) the temperature of the reaction; and (5) the presence of certain organic solvents, such as formamide, which decrease DNA duplex stability. In general, the longer the probe, the higher the temperature required for proper annealing. A common approach is to vary the temperature; higher relative temperatures result in more stringent reaction conditions. To hybridize under "stringent conditions" describes hybridization protocols in which polynucleotides at least 60% homologous to each other remain hybridized. Generally, stringent conditions are selected to be about 5ºC lower than the thermal melting point (Tm) for the specific sequence at a defined ionic strength and pH. The Tm is the temperature (under defined ionic strength, pH, and polynucleotide concentration) at which 50% of the probes complementary to the given sequence hybridize to the given sequence at equilibrium. Since the given sequences are generally present at excess, at Tm, 50% of the probes are occupied at equilibrium. "Stringent hybridization conditions" are conditions that enable a probe, primer, or oligonucleotide to hybridize only to its specific sequence. Stringent conditions are sequence- dependent and will differ. Stringent conditions typically comprise: (1) low ionic strength and high temperature washes, for example 15 mM sodium chloride, 1.5 mM sodium citrate, 0.1% sodium dodecyl sulfate, at 50ºC; (2) a denaturing agent during hybridization, for example, 50% (v / v) formamide, 0.1% bovine serum albumin, 0.1% Ficoll, 0.1% polyvinylpyrrolidone, 50 mM sodium phosphate buffer (750 mM sodium chloride, 75 mM sodium citrate; pH 6.5), at 42ºC; or (3) 50% formamide. Washes typically also comprise 5 x SSC (0.75 M NaCl, 75 mM sodium citrate), 50 mM sodium phosphate (pH 6.8), 0.1% sodium pyrophosphate, 5xDenhardt's solution, sonicated salmon sperm DNA (50 µg / mL), 0.1% SDS, and 10% dextran sulfate at 42ºC, with a wash at 42ºC in 0.2xSSC (sodium chloride / sodium citrate) and 50% formamide at 55ºC, followed by a high-stringency wash consisting of 0.1xSSC containing EDTA at 55ºC. Suitably, the conditions are such that sequences at least about 65%, 70%, 75%, 85%, 90%, 95%, 98%, or 99% homologous to each other typically remain hybridized to each other. "Moderately stringent conditions" use washing solutions and hybridization conditions that are less stringent, such that a polynucleotide will hybridize to the entire, fragments, derivatives, or analogs of the polynucleotide. One example comprises hybridization in 6xSSC, 5xDenhardt's solution, 0.5% SDS and 100 µg / mL denatured salmon sperm DNA at 55ºC, followed by one or more washes in 1xSSC, 0.1% SDS at 37ºC. The temperature, ionic strength, etc., can be adjusted to accommodate experimental factors such as probe length. Other moderate stringency conditions have been described (see Ausubel et al., Current Protocols in Molecular Biology, Volumes 1-3, John Wiley & Sons, Inc., Hoboken, N.J. (1993); Kriegler, Gene Transfer and Expression: A Laboratory Manual, Stockton Press, New York, N.Y. (1990); Perbal, A Practical Guide to Molecular Cloning, 2nd edition, John Wiley & Sons, New York, N.Y. (1988)). "Low stringent conditions" use washing solutions and hybridization conditions that are less stringent than those for moderate stringency, such that a polynucleotide will hybridize to the entire, fragments, derivatives, or analogs of the polynucleotide. A non-limiting example of low stringency hybridization conditions includes hybridization in 35% formamide, 5xSSC, 50 mM Tris HCl (pH 7.5), 5 mM EDTA, 0.02% PVP, 0.02% Ficoll, 0.2% BSA, 100 µg / mL denatured salmon sperm DNA, 10% (wt / vol) dextran sulfate at 40ºC, followed by one or more washes in 2xSSC, 25 mM Tris HCl (pH 7.4), 5 mM EDTA, and 0.1% SDS at 50ºC. The term "plant" refers to any plant at any stage of its life cycle or development, and its progenies. In one embodiment, the plant is a tobacco plant, which refers to a plant belonging to the genus Nicotiana. The term includes reference to whole plants, plant organs, plant tissues, plant propagules, plant seeds, plant cells and progeny of same. Plant cells include, without limitation, cells from seeds, suspension cultures, embryos, meristematic regions, callus tissue, leaves, roots, shoots, gametophytes, sporophytes, pollen, and microspores. Suitable species, cultivars, hybrids and varieties of tobacco plant are described herein. "Polynucleotide", "polynucleotide sequence" or "polynucleotide fragment" are used interchangeably herein and refer to a polymer of RNA or DNA that is single- or double- stranded, optionally containing synthetic, non-natural or altered nucleotide bases. Nucleotides (usually found in their 5'-monophosphate form) are referred to by their single letter designation as follows: "A" for adenylate or deoxyadenylate (for RNA or DNA, respectively), "C" for cytidylate or deoxycytidylate, "G" for guanylate or deoxyguanylate, "U" for uridylate, "T" for deoxythymidylate, "R" for purines (A or G), "Y" for pyrimidines (C or T), "K" for G or T, "H" for A or C or T, "I" for inosine, and "N" for any nucleotide. A polynucleotide can be, without limitation, a genomic DNA, complementary DNA (cDNA), mRNA, or antisense RNA or a fragment(s) thereof. Moreover, a polynucleotide can be single-stranded or double-stranded, a mixture of single-stranded and double-stranded regions, a hybrid molecule comprising DNA and RNA, or a hybrid molecule with a mixture of single-stranded and double-stranded regions or a fragment(s) thereof. In addition, the polynucleotide can be composed of triple-stranded regions comprising DNA, RNA, or both or a fragment(s) thereof. A polynucleotide can contain one or more modified bases, such as phosphothioates, and can be a peptide nucleic acid (PNA). Generally, polynucleotides can be assembled from isolated or cloned fragments of cDNA, genomic DNA, oligonucleotides, or individual nucleotides, or a combination of the foregoing. Although the polynucleotides described herein are shown as DNA sequences, the polynucleotides include their corresponding RNA sequences, and their complementary (for example, completely complementary) DNA or RNA sequences, including the reverse complements thereof. The polynucleotides of the present disclosure are set forth in the accompanying sequence listing. "Polypeptide” or "polypeptide sequence" refer to a polymer of amino acids in which one or more amino acid residues is an artificial chemical analogue of a corresponding naturally occurring amino acid, as well as to naturally occurring polymers of amino acids. The terms are also inclusive of modifications including, but not limited to, glycosylation, lipid attachment, sulfation, gamma-carboxylation of glutamic acid residues, hydroxylation and ADP-ribosylation. The polypeptides of the present disclosure are set forth in the accompanying sequence listing. “Recombinant" as used herein refers to an artificial combination of two otherwise separated segments of sequence – such as by chemical synthesis or by the manipulation of isolated segments of polynucleotides by genetic engineering techniques. The term also includes reference to a cell or vector, that has been modified by the introduction of a heterologous polynucleotide or a cell derived from a cell so modified, but does not encompass the alteration of the cell or vector by naturally occurring events (for example, spontaneous mutation, natural transformation or transduction or transposition) such as those occurring without deliberate human intervention. The term “tobacco” is used in a collective sense to refer to tobacco crops (for example, a plurality of tobacco plants grown in the field and not hydroponically grown tobacco), tobacco plants and parts thereof, including but not limited to, roots, stems, leaves, flowers, and seeds prepared and / or obtained, as described herein. In one embodiment, the term excludes propagating material. It is understood that “tobacco” refers to Nicotiana tabacum plants and products thereof. The term “tobacco products” refers to consumer tobacco products, including but not limited to, smoking materials (for example, cigarettes, cigars, and pipe tobacco), snuff, chewing tobacco, gum, and lozenges, as well as components, materials and ingredients for manufacture of consumer tobacco products. Suitably, these tobacco products are manufactured from tobacco leaves and stems harvested from tobacco and cut and / or dried and / or cured and / or fermented according to conventional techniques in tobacco preparation. “Variant” with respect to a peptide or polypeptide means a peptide or polypeptide that differs in sequence by the insertion, deletion, or conservative substitution of amino acids, but retain at least one biological function or activity. Variant may also mean a polypeptide that retains at least one biological function or activity. A conservative substitution of an amino acid, that is, replacing an amino acid with a different amino acid of similar properties (for example, hydrophilicity, degree and distribution of charged regions) is recognized in the art as typically involving a minor change. A variant peptide or polypeptide of the mutated peptide or polypeptide described here will be a variant that contains one or more mutations according to the present disclosure and additionally contains one or more insertions, deletions, or conservative substitutions of one or more further amino acids, whilst retaining at least one biological function or activity. The term "variety" refers to a population of plants that share constant characteristics which separate them from other plants of the same species. While possessing one or more distinctive traits, a variety is further characterized by a very small overall variation between individuals within that variety. A variety is often sold commercially. "Vector" refers to a polynucleotide vehicle that comprises a combination of polynucleotide components for enabling the transport of polynucleotides, polynucleotide constructs and polynucleotide conjugates and the like. A vector may be a viral vector, bacteriophage, bacterial artificial chromosome or yeast artificial chromosome. A vector may be a DNA or RNA vector. Suitable vectors include episomes capable of extra-chromosomal replication such as circular, double-stranded nucleotide plasmids; linearized double-stranded nucleotide plasmids; and other vectors of any origin. An "expression vector" as used herein is a polynucleotide vehicle that comprises a combination of polynucleotide components for enabling the expression of polynucleotide(s), polynucleotide constructs and polynucleotide conjugates and the like. Suitable expression vectors include episomes capable of extra-chromosomal replication such as circular, double- stranded nucleotide plasmids; linearized double-stranded nucleotide plasmids; and other functionally equivalent expression vectors of any origin. An expression vector comprises at least a promoter positioned upstream and operably-linked to a polynucleotide, polynucleotide constructs or polynucleotide conjugate, as defined below. Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those of ordinary skill in the art. For example, any nomenclatures used in connection with, and techniques of, cell and tissue culture, molecular biology, immunology, microbiology, genetics and polypeptide and polynucleotide chemistry and hybridization described herein are those that are well known and commonly used in the art. The meaning and scope of the terms should be clear; in the event however of any latent ambiguity, definitions provided herein take precedent over any dictionary or extrinsic definition. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular. “Genome editing" refers to changing an endogenous gene that encodes an endogenous polypeptide, such that polypeptide expression of a truncated endogenous polypeptide or an endogenous polypeptide having an amino acid modification - such as a substitution - is obtained. Genome editing can include replacing the region of the endogenous gene to be targeted or replacing the entire endogenous gene with a copy of the gene that has a truncation or an amino acid substitution with a repair mechanism – such as homology- directed repair. Genome editing may also include generating an amino acid substitution in the endogenous gene by generating a double stranded break in the endogenous gene that is then repaired using a non-homologous end joining (NHEJ) pathway. NHEJ may add or delete at least one base pair during repair which may generate an amino acid substitution. Genome editing may also include deleting a gene segment by the simultaneous action of two nucleases on the same DNA strand in order to create a truncation between the two nuclease target sites and repairing the DNA break by NHEJ. DETAILED DESCRIPTION The polynucleotide(s) described herein encode an active QS polypeptide that has at least about 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100% of the function or activity of the polypeptide(s) shown in the sequence listing. In certain embodiments, the polynucleotide sequence comprises, consists or consists essentially of a sequence having at least 80% sequence identity to any of the sequences described herein, including any of the polynucleotides shown in the sequence listing. Suitably, the isolated polynucleotide comprises, consists or consists essentially of a sequence having at least 80%, 85%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% 96%, 97%, 98%, 99% or 100% sequence identity thereto. For example, the isolated polynucleotide comprises, consists or consists essentially of a sequence having at least 80%, 85%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% 96%, 97%, 98%, 99% or 100% sequence identity to SEQ ID NO: 4. There is disclosed a polynucleotide sequence encoding a NtQS-T QS polypeptide comprising a contiguous polypeptide sequence of SEQ ID NO: 3, wherein the cysteine at amino acid position 133 of SEQ ID NO: 3 is altered for an amino acid that modulates (total) alkaloid and optionally nitrate levels in cured or dried leaf as compared to cured or dried leaf obtained from a control plant. Levels of TSNAs – such as NAB, NNK, NAT and NNN - in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from the control plant can also be modulated. Suitably, the cysteine at amino acid position 133 of NtQS-T is substituted in the mutated polypeptide. Suitably, the cysteine at amino acid position 133 of NtQS-T is substituted for an aromatic amino acid selected from the group consisting of histidine, phenylalaine, tryptophan, asparagine and tyrosine. Suitably, the cysteine at amino acid position 133 of NtQS-T is substituted for tyrosine (C133Y) in the mutated polypeptide. Suitably, the polynucleotide sequence comprises, consists or consists essentially of the polynucleotide sequence set forth in SEQ ID NO: 4. SEQ ID NO: 4 is a mutant polynucleotide sequence. There is also disclosed polynucleotide fragments of SEQ ID NO: 4 encoding a QS polypeptide including the mutation with substantial homology (that is, sequence similarity) or substantial identity thereto that have at least about 80%, 85%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9% or 100% sequence identity to the corresponding fragments of SEQ ID NO: 4. According to the present disclosure, a polynucleotide sequence encoding the mutation in NtQS-T is incorporated into a tobacco plant or cell thereof. Fragments of the polynucleotides incorporating the mutation(s) described herein are also disclosed. Polynucleotide fragments typically comprise at least 10, at least 20, at least 30, at least 40, at least 50, at least 100 or at least 200 contiguous nucleotides. A polynucleotide as described herein can include a polymer of nucleotides, which may be unmodified or modified deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). Accordingly, a polynucleotide can be, without limitation, a genomic DNA, complementary DNA (cDNA), mRNA, or antisense RNA or a fragment(s) or truncate(s) thereof. Moreover, a polynucleotide can be single-stranded or double-stranded DNA, DNA that is a mixture of single-stranded and double-stranded regions, a hybrid molecule comprising DNA and RNA, or a hybrid molecule with a mixture of single-stranded and double-stranded regions or a fragment(s) thereof. In addition, the polynucleotide can be composed of triple-stranded regions comprising DNA, RNA, or both or a fragment(s) thereof. Generally, polynucleotides can be assembled from isolated or cloned fragments of cDNA, genomic DNA, oligonucleotides, or individual nucleotides, or a combination of the foregoing. Although the polynucleotides described herein are shown as DNA sequences, they include their corresponding RNA sequences, and their complementary (for example, completely complementary) DNA or RNA sequences, including the reverse complements thereof. A polynucleotide as described herein will generally contain phosphodiester bonds. Other analogue polynucleotides include those with positive backbones; non-ionic backbones, and non-ribose backbones. Modifications of the ribose-phosphate backbone may be done for a variety of reasons, for example, to increase the stability and half-life of such molecules in physiological environments or as probes on a biochip. Mixtures of naturally occurring polynucleotides and analogues can be made; alternatively, mixtures of different polynucleotide analogues, and mixtures of naturally occurring polynucleotides and analogues may be made. Analogue polynucleotides can include those with positive backbones, non-ionic backbones and non-ribose backbones. Polynucleotides containing one or more carbocyclic sugars are also included. Other analogues include peptide polynucleotides which are peptide polynucleotide analogues. These backbones are substantially non-ionic under neutral conditions, in contrast to the highly charged phosphodiester backbone of naturally occurring polynucleotides. This may result in advantages. First, the peptide polynucleotide backbone may exhibit improved hybridization kinetics. Peptide polynucleotides have larger changes in the melting temperature for mismatched versus perfectly matched base pairs. DNA and RNA typically exhibit a 2-4 °C drop in melting temperature for an internal mismatch. With the non-ionic peptide polynucleotide backbone, the drop is closer to 7-9 °C. Similarly, due to their non- ionic nature, hybridization of the bases attached to these backbones is relatively insensitive to salt concentration. In addition, peptide polynucleotides may not be degraded or degraded to a lesser extent by cellular enzymes, and thus may be more stable. Among the uses of the disclosed polynucleotides, and fragments thereof, is the use of fragments as probes in hybridisation assays or primers for use in amplification assays. Such fragments generally comprise at least about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 or more contiguous nucleotides of a DNA sequence. In other embodiments, a DNA fragment comprises at least about 10, 15, 20, 30, 40, 50 or 60 or more contiguous nucleotides of a DNA sequence. Thus, in one aspect, there is also provided a method for detecting a polynucleotide comprising the use of the probes or primers or both. The basic parameters affecting the choice of hybridization conditions and guidance for devising suitable conditions are described by Sambrook, J., E. F. Fritsch, and T. Maniatis (1989, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.). Using knowledge of the genetic code in combination with the polypeptide sequences described herein, sets of degenerate oligonucleotides can be prepared. Such oligonucleotides are useful as primers, for example, in polymerase chain reactions (PCR), whereby DNA fragments are isolated and amplified. In certain embodiments, degenerate primers can be used as probes for genetic libraries. Such libraries include cDNA libraries, genomic libraries, and even electronic express sequence tag or DNA libraries. Homologous sequences identified by this method would then be used as probes to identify homologues of the sequences identified herein. Also of potential use are polynucleotides and oligonucleotides (for example, primers or probes) that hybridize under decreased stringency conditions, typically moderately stringent conditions, and commonly highly stringent conditions to the polynucleotide(s), as described herein. The basic parameters affecting the choice of hybridization conditions and guidance for devising suitable conditions are set forth by Sambrook, J., E. F. Fritsch, and T. Maniatis (1989, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. and can be readily determined by those having ordinary skill in the art based on, for example, the length or base composition of the polynucleotide. One way of achieving moderately and high stringent conditions is defined herein. It should be understood that the wash temperature and wash salt concentration can be adjusted as necessary to achieve a desired degree of stringency by applying the basic principles that govern hybridization reactions and duplex stability, as known to those skilled in the art and described further below (see, for example, Sambrook, J., E. F. Fritsch, and T. Maniatis (1989, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y). When hybridizing a polynucleotide to a polynucleotide of unknown sequence, the hybrid length is assumed to be that of the hybridizing polynucleotide. When polynucleotides of known sequence are hybridized, the hybrid length can be determined by aligning the sequences of the polynucleotides and identifying the region or regions of optimal sequence complementarity. The hybridization temperature for hybrids anticipated to be less than 50 base pairs in length should be 5 to 10 °C less than the melting temperature of the hybrid, where melting temperature is determined according to the following equations. For hybrids less than 18 base pairs in length, melting temperature (°C)=2(number of A+T bases)+4(number of G+C bases). For hybrids above 18 base pairs in length, melting temperature (°C)=81.5+16.6(log10 [Na+])+0.41(% G+C)-(600 / N), where N is the number of bases in the hybrid, and [Na+] is the concentration of sodium ions in the hybridization buffer ([Na+] for 1x Standard Sodium Citrate=0.165M). Typically, each such hybridizing polynucleotide has a length that is at least 25% (commonly at least 50%, 60%, or 70%, and most commonly at least 80%) of the length of a polynucleotide to which it hybridizes, and has at least 60% sequence identity (for example, at least 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99% or 100%) with a polynucleotide to which it hybridizes. As will be understood by the person skilled in the art, a linear DNA has two possible orientations: the 5'-to-3' direction and the 3'-to-5' direction. For example, if a first sequence is positioned in the 5'-to-3' direction, and if a second sequence is positioned in the 5'-to-3' direction within the same polynucleotide molecule / strand, then the first sequence and the second sequence are orientated in the same direction, or have the same orientation. Typically, a promoter sequence and a gene of interest under the regulation of the given promoter are positioned in the same orientation. However, with respect to the first sequence positioned in the 5'-to-3' direction, if a second sequence is positioned in the 3'-to-5' direction within the same polynucleotide molecule / strand, then the first sequence and the second sequence are orientated in anti-sense direction, or have anti-sense orientation. Two sequences having anti-sense orientations with respect to each other can be alternatively described as having the same orientation, if the first sequence (5'-to-3' direction) and the reverse complementary sequence of the first sequence (first sequence positioned in the 5'- to-3') are positioned within the same polynucleotide molecule / strand. The sequences set forth herein are shown in the 5'-to-3' direction. Vectors containing recombinant polynucleotide constructs such as those described herein are also provided. Suitable vector backbones include, for example, those routinely used in the art such as plasmids, viruses, artificial chromosomes, bacterial artificial chromosomes, yeast artificial chromosomes, or bacteriophage artificial chromosomes. Suitable expression vectors include, without limitation, plasmids and viral vectors derived from, for example, bacteriophage, baculoviruses, and retroviruses. Numerous vectors and expression systems are commercially available. In one aspect, there is provided an isolated polypeptide comprising, consisting or consisting essentially of a polypeptide having at least 80% sequence identity to any of the polypeptides described herein, including any of the polypeptides shown in the sequence listing. Suitably, the isolated polypeptide comprises, consists or consists essentially of a sequence having at least 80%, 85%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9% or 100% sequence identity thereto. For example, the isolated polypeptide comprises, consists or consists essentially of a sequence having at least 80%, 85%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9% or 100% sequence identity to SEQ ID NO: 5. For example, the isolated polypeptide comprises, consists or consists essentially of a sequence having at least 80%, 85%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9% or 100% sequence identity to SEQ ID NO: 5, with the proviso that the mutation in SEQ ID NO: 5 is retained in the sequence having at least 80%, 85%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8% or 99.9% sequence identity to SEQ ID NO: 5. In another aspect, there is disclosed a polypeptide sequence encoded by the polynucleotide sequence described herein. SEQ ID NO: 5 is a mutant polypeptide. In another aspect, there is disclosed a NtQS-T QS comprising a contiguous polypeptide sequence of SEQ ID NO: 3, wherein the cysteine at amino acid position 133 of SEQ ID NO: 4 is altered for an amino acid that modulates (total) alkaloid and optionally nitrate levels in cured or dried leaf as compared to cured or dried leaf obtained from a control plant. Levels of TSNAs – such as NAB, NNK, NAT and NNN - in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from the control plant can also be modulated. Suitably, the cysteine at amino acid position 133 of NtQS-T is substituted in the mutated polypeptide. Suitably, the cysteine at amino acid position 133 of NtQS-T is substituted for an aromatic amino acid selected from the group consisting of histidine, phenylalaine, tryptophan, asparagine and tyrosine. Suitably, the cysteine at amino acid position 133 of NtQS-T is substituted for tyrosine (C133Y) in the mutated polypeptide. Suitably, the altered or mutated polypeptide comprises the contiguous polypeptide sequence of SEQ ID NO: 5. Suitably, the altered or mutated polypeptide comprises, consists or consists essentially of the polypeptide sequence set forth in SEQ ID NO: 5. According to the present disclosure, the mutant polypeptide is incorporated into a tobacco plant. Fragments of the polypeptides incorporating the mutation(s) described herein are also disclosed. The fragments of the polypeptide(s) typically retain some or all of the function or activity of the full-length sequence. Polypeptide fragments typically comprise at least 10, at least 20, at least 30, at least 40, at least 50, at least 100 or at least 200 contiguous amino acids. The polypeptides disclosed herein include at least one mutation produced by introducing any type of one or more alterations, which can be isolated naturally. The function or activity of the QS polypeptide into which the mutation(s) is introduced may be modulated (for example, reduced or decreased) by the introduction of the mutation. The levels of (total) alkaloids and optionally nitrate in cured or dried leaf obtained from a plant or plant cell carrying the mutation described herein is modulated (for example, reduced or decreased). Levels of TSNAs – such as NAB, NNK, NAT and NNN - in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from the control plant can also be modulated (for example, decreased). Suitably, the mutation is a substitution. A substitution refers to the replacement of at least one amino acid of the QS polypeptide with another amino acid having similar properties (such as similar hydrophobicity, hydrophilicity, antigenicity, propensity to form or break alpha-helical structures or β-sheet structures and the like). A plant or plant cell comprising or carrying a mutation in one or more polynucleotides or polypeptides described herein is disclosed. The mutation results in modulated (total) alkaloid and optionally nitrate levels in cured or dried leaf obtained from the plant or plant cell as described herein. The mutation can also result in modulated levels of TSNAs – such as NAB, NNK, NAT and NNN - in cured or dried leaf obtained from the plant or plant cell as described herein. When grown under hydroponics conditions in a greenhouse, the mutation may also result in modulated levels of nitrate in cured or dried leaf obtained from the plant or plant cell, as shown in Example 3 and Table 1. When grown under field conditions, the mutation does not result in significantly modulated levels of nitrate in cured or dried leaf obtained from the plant or plant cell as shown in Example 4 and Table 2. Thus, according to certain embodiments, the modulated levels in the mutant are obtained only under field conditions. According to certain other embodiments, the modulated levels in the mutant are obtained under hydroponics conditions in a greenhouse. In one embodiment, the levels of nitrate are not modulated when the mutant plant is grown under field conditions. In another embodiment, the levels of nitrate are not modulated in the mutant plant. Suitably, the Nicotiana tabacum plant is a field grown Nicotiana tabacum plant or part thereof. Mutations described herein can include man-made mutations or synthetic mutations. Mutations in the polynucleotides and polypeptides described herein can be mutations that are obtained or obtainable via a process which includes an in vitro or an in vivo manipulation step. Mutations in the polynucleotides and polypeptides described herein can be mutations that are obtained or obtainable via a process which includes intervention by man. There is provided a method for modulating the level of a polypeptide in a (cured) plant or in (cured) plant material said method comprising introducing into the genome of said plant at least one mutation that is selected from the sequences according to the present disclosure – such as C133Y. Suitably, the gene encodes the Nicotiana tabacum QS polypeptide as described herein. There is also disclosed a plant or plant cell that is heterozygous or homozygous for one or more mutations according to the present disclosure. Methods for obtaining mutant polynucleotides and polypeptides as described herein are also disclosed. A plant of interest – such as tobacco, including a plant cell or plant material, can be genetically modified by various methods known to induce mutagenesis, including site- directed mutagenesis, oligonucleotide-directed mutagenesis, chemically-induced mutagenesis, irradiation-induced mutagenesis, mutagenesis utilizing modified bases, mutagenesis utilizing gapped duplex DNA, double-strand break mutagenesis, mutagenesis utilizing repair-deficient host strains, mutagenesis by total gene synthesis, DNA shuffling and other methods as discussed below. Methods that introduce mutations randomly in a polynucleotide can include chemical mutagenesis and radiation mutagenesis. Methods that introduce one or more targeted mutations into a polynucleotide sequence include but are not limited to genome editing technology, particularly zinc finger nuclease- mediated mutagenesis, tilling (targeting induced local lesions in genomes), homologous recombination, oligonucleotide-directed mutagenesis, and meganuclease-mediated mutagenesis. Such methods are well known in the art and are described in WO2020 / 141062, for example. Another method of genome editing involves the use of the bacterial CRISPR / Cas system. CRISPR / Cas technology was implemented in plants in WO2015 / 189693, which discloses a viral-mediated genome editing platform that is broadly applicable across plant species. In the context of the present disclosure, a guide RNA may be derived from any of the sequences disclosed herein and in the teaching of WO2015 / 189693 to edit the genome of a plant cell and obtain a desired mutant plant. The fast pace of the development of the technology has generated a great variety of protocols with broad applicability in plantae, which have been well catalogued in a number of recent scientific review articles (for example, Plant Methods (2016) 12:8; and Front Plant Sci. (2016) 7:506). A review of CRISPR / Cas systems with a particular focus on its application is described in Biotechnology Advances (2015) 33, 1, 41- 52). More recent developments in the use of CRISPR / Cas for manipulating plant genomes are discussed in Acta Pharmaceutica Sinica B (2017) 7, 3, 292-302 and Curr. Op. in Plant Biol. (2017) 36, 1–8. CRISPR / Cas9 plasmids for use in plants are listed in “addgene”, the non-profit plasmid repository (addgene.org), and CRISPR / Cas plasmids are commercially available. One or more introduced mutations – such as the mutation described herein - can be identified or selected using methods known to those of skill in the art - such as Southern blot analysis, DNA sequencing, PCR analysis, or phenotypic analysis. Mutations can be determined using methods that are well known in the art. The plants or plant cells according to the present disclosure comprise the mutation described herein and optionally any combination of one or more further mutations in one or more genes. For example, the plants or plant cells may have a single mutation in a single gene – such as the C133Y mutation in NtQS-T; multiple mutations in a single gene; a single mutation in two or more or three or more or four or more genes; or multiple mutations in two or more or three or more or four or more genes. In one embodiment, seeds from plants are mutagenised and then grown into first generation mutant plants. The first-generation plants are then allowed to self-pollinate and seeds from the first-generation plant are grown into second generation plants, which are then screened for mutations – such as the mutation described herein - in their loci. Though the mutagenized plant material can be screened for mutations, an advantage of screening the second-generation plants is that all somatic mutations correspond to germline mutations. One of skill in the art will understand that a variety of plant materials, including but not limited to, seeds, pollen, plant tissue or plant cells, may be mutagenised to create the mutant plants. However, the type of plant material mutagenised may affect when the plant polynucleotide is screened for mutations. For example, when pollen is subjected to mutagenesis prior to pollination of a non-mutagenized plant the seeds resulting from that pollination are grown into first generation plants. Every cell of the first-generation plants will contain mutations created in the pollen; thus these first generation plants may then be screened for mutations instead of waiting until the second generation. Prepared polynucleotide from individual plants, plant cells, or plant material can optionally be pooled to expedite screening for at least the mutation described herein in the population of plants originating from the mutagenized plant tissue, cells or material. One or more subsequent generations of plants, plant cells or plant material can be screened. The size of the optionally pooled group is dependent upon the sensitivity of the screening method used. After the samples are optionally pooled, they can be subjected to polynucleotide-specific amplification techniques, such as PCR. Any one or more primers or probes specific to the gene or the sequences immediately adjacent to the gene may be utilized to amplify the sequences within the optionally pooled sample. Suitably, the one or more primers or probes are designed to amplify the regions of the locus where useful mutations are most likely to arise. Most suitably, the primer is designed to detect mutations within regions of the polynucleotide. Suitably, the primer(s) and probe(s) avoid known polymorphic sites to ease screening for point mutations. To facilitate detection of amplification products, the one or more primers or probes may be labelled using any conventional labelling method. Primer(s) or probe(s) can be designed based upon the sequences described herein using methods that are well understood in the art. To facilitate detection of amplification products, the primer(s) or probe(s) may be labelled using any conventional labelling method. These can be designed based upon the sequences described herein using methods that are well understood in the art. Polymorphisms may be identified by means known in the art and some have been described in the literature. Accordingly, in a further aspect there is provided a method of preparing a plant comprising the mutation described herein. The method involves providing at least one cell of a plant comprising a gene encoding a functional QS polynucleotide. Next, the at least one cell of the plant is treated under conditions effective to incorporate at least one mutation into the QS polynucleotide as described herein. The at least one mutant plant cell is then propagated into a mutant plant, where the mutant plant has a modulated levels of (total) alkaloid and optionally nitrate levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant. Levels of TSNAs – such as NAB, NNK, NAT and NNN - can also be modulated. In one embodiment, the treating step involves subjecting the at least one cell to a chemical mutagenising agent as described herein and under conditions effective to yield at least one mutant plant cell. In another embodiment of this method, the treating step involves subjecting the at least one cell to a radiation source under conditions effective to yield at least one mutant plant cell. The term "mutant plant" includes mutant plants in which the genotype is modified as compared to a control plant, suitably by means other than genetic engineering or genetic modification. In certain embodiments, the mutant plant, mutant plant cell or mutant plant material may comprise one or more mutations that have occurred naturally in another plant, plant cell or plant material and confer a desired trait. This mutation can be incorporated (for example, introgressed) into another plant, plant cell or plant material (for example, a plant, plant cell or plant material with a different genetic background to the plant from which the mutation was derived) to confer the trait thereto. Thus, by way of example, a mutation that occurred naturally in a first plant may be introduced into a second plant – such as a second plant with a different genetic background to the first plant. The skilled person is therefore able to search for and identify a plant carrying naturally in its genome one or more mutant alleles of the genes described herein which confer a desired trait. The mutant allele(s) that occurs naturally can be transferred to the second plant by various methods including breeding, backcrossing and introgression to produce lines, varieties or hybrids that have one or more mutations in the genes described herein. The same technique can also be applied to the introgression of one or more non-naturally occurring mutation(s) from a first plant into a second plant. Plants showing a desired trait may be screened out of a pool of mutant plants. Suitably, the selection is carried out utilising the knowledge of the polynucleotide as described herein. Consequently, it is possible to screen for a genetic trait as compared to a control. Such a screening approach may involve the application of conventional amplification and / or hybridization techniques as discussed herein. Thus, a further aspect of the present disclosure relates to a method for identifying a mutant plant comprising the steps of: (a) providing a sample comprising polynucleotide from a plant; and (b) determining the sequence of the polynucleotide, wherein a difference in the sequence of the polynucleotide as compared to the polynucleotide of a control plant is indicative that said plant is a mutant plant. In another aspect there is provided a method for identifying a mutant plant in which the leaves thereof contain modulated (for example, reduced or decreased) levels of (total) alkaloid and optionally nitrate as compared to leaves derived from a control plant comprising the steps of: (a) providing a sample from a plant to be screened; (b) determining if said sample comprises one or more mutations as described herein in a QS polynucleotide; and (c) determining the level of (total) alkaloid and optionally nitrate in said plant. Suitably the level of (total) alkaloid and optionally nitrate is determined in cured or dried leaves. Levels of TSNAs – such as NAB, NNK, NAT and NNN - can also be modulated. In another aspect there is provided a method for preparing a mutant plant which has decreased levels of (total) alkaloid and optionally nitrate as compared to a control plant comprising the steps of: (a) providing a sample from a first plant; (b) determining if said sample comprises one or more mutations as described herein in a QS polynucleotide that results in decreased levels of (total) alkaloid and optionally nitrate; and (c) transferring the one or more mutations into a second plant. Suitably the level of (total) alkaloid and optionally nitrate is determined in dried or cured leaves. Levels of TSNAs – such as NAB, NNK, NAT and NNN - can also be modulated. The mutation(s) can be transferred into the second plant using various methods that are known in the art – such as by genetic engineering, genetic manipulation, introgression, plant breeding, backcrossing and the like. In one embodiment, the first plant is a naturally occurring plant. In one embodiment, the second plant has a different genetic background to the first plant. In another aspect there is provided a method for preparing a mutant plant which has decreased levels of (total) alkaloid and optionally nitrate as compared to a control plant comprising the steps of: (a) providing a sample from a first plant; (b) determining if said sample comprises one or more mutations as described herein in a QS polynucleotide that results in decreased levels of (total) alkaloid and optionally nitrate; and (c) introgressing the one or more mutations from the first plant into a second plant. Suitably the level of (total) alkaloid and optionally nitrate is determined in dried or cured leaves. Levels of TSNAs – such as NAB, NNK, NAT and NNN - can also be modulated. In one embodiment, the step of introgressing comprises plant breeding, optionally including backcrossing and the like. In one embodiment, the first plant is a naturally occurring plant. In one embodiment, the second plant has a different genetic background to the first plant. In one embodiment, the first plant is not a cultivar or an elite cultivar. In one embodiment, the second plant is a cultivar or an elite cultivar. A further aspect relates to a mutant plant (including a cultivar or elite cultivar mutant plant) obtained or obtainable by the methods described herein. In certain embodiments, the “mutant plants” may have one or more mutations localised only to a specific region of the plant – such as within the sequence of the one or more polynucleotide(s) described herein. According to this embodiment, the remaining genomic sequence of the mutant plant will be the same or substantially the same as the plant prior to the mutagenesis. In a further aspect there is provided a method of identifying a plant, a plant cell or plant material comprising a mutation in a gene encoding a QS polynucleotide comprising: (a) subjecting a plant, a plant cell or plant material to mutagenesis; (b) obtaining a sample from said plant, plant cell or plant material or descendants thereof; and (c) determining the presence of a mutated polynucleotide sequence carrying the mutation described herein. The disclosed compositions and methods are applied to Nicotiana tabacum. Suitably, the Nicotiana tabacum is grown under field conditions – such as according to the agricultural practices of Grandes cultures fiches techniques, agridea - developpement de l’agriculture et de l’espace rural, www.agridea.ch). The use of tobacco cultivars and elite tobacco cultivars is also contemplated herein. The plant may therefore be a tobacco variety or elite tobacco cultivar that comprises one or more genetic mutations. The genetic mutation(s) (for example, one or more polymorphisms) can be mutations that do not exist naturally in the individual tobacco variety or tobacco cultivar (for example, elite tobacco cultivar) or can be genetic mutation(s) that do occur naturally provided that the mutation does not occur naturally in the individual tobacco variety or tobacco cultivar (for example, elite tobacco cultivar). Nicotiana tabacum varieties include Burley type, dark type, flue-cured type, and Oriental type tobaccos. Non-limiting examples of varieties or cultivars are: AA37, BD 64, CC 101, CC 200, CC 27, CC 301, CC 400, CC 500, CC 600, CC 700, CC 800, CC 900, Coker 176, Coker 319, Coker 371 Gold, Coker 48, CD 263, DF911, DT 538 LC Galpao tobacco, GL 26H, GL 350, GL 600, GL 737, GL 939, GL 973, HB 04P, HB 04P LC, HB3307PLC, Hybrid 403LC, Hybrid 404LC, Hybrid 501 LC, K 149, K 326, K 346, K 358, K394, K 399, K 730, KDH 959, KT 200, KT204LC, KY10, KY14, KY 160, KY 17, KY 171, KY 907, KY907LC, KY14xL8 LC, Little Crittenden, McNair 373, McNair 944, msKY 14xL8, Narrow Leaf Madole, Narrow Leaf Madole LC, NBH 98, N-126, N-777LC, N-7371LC, NC 100, NC 102, NC 2000, NC 291, NC 297, NC 299, NC 3, NC 4, NC 5, NC 6, NC7, NC 606, NC 71, NC 72, NC 810, NC BH 129, NC 2002, Neal Smith Madole, OXFORD 207, PD 7302 LC, PD 7309 LC, PD 7312 LC, ’Perique' tobacco, PVH03, PVH09, PVH19, PVH50, PVH51, R 610, R 630, R 7-11, R 7-12, RG 17, RG 81, RG H51, RGH 4, RGH 51, RS 1410, Speight 168, Speight 172, Speight 179, Speight 210, Speight 220, Speight 225, Speight 227, Speight 234, Speight G-28, Speight G- 70, Speight H-6, Speight H20, Speight NF3, TI 1406, TI 1269, TN 86, TN86LC, TN 90, TN 97, TN97LC, TN D94, TN D950, TR (Tom Rosson) Madole, VA 309, VA359, AA 37-1, B13P, Xanthi (Mitchell-Mor), Bel-W3, 79-615, Samsun Holmes NN, KTRDC number 2 Hybrid 49, Burley 21, KY8959, KY9, MD 609, PG01, PG04, PO1, PO2, PO3, RG11, RG 8, VA509, AS44, Banket A1, Basma Drama B84 / 31, Basma I Zichna ZP4 / B, Basma Xanthi BX 2A, Batek, Besuki Jember, C104, Coker 347, Criollo Misionero, Delcrest, Djebel 81, DVH 405, Galpão Comum, HB04P, Hicks Broadleaf, Kabakulak Elassona, Kutsage E1, LA BU 21, NC 2326, NC 297, PVH 2110, Red Russian, Samsun, Saplak, Simmaba, Talgar 28, Wislica, Yayaldag, Prilep HC-72, Prilep P23, Prilep PB 156 / 1, Prilep P12-2 / 1, Yaka JK-48, Yaka JB 125 / 3, TI-1068, KDH-960, TI-1070, TW136, Basma, TKF 4028, L8, TKF 2002, GR141, Basma xanthi, GR149, GR153, Petit Havana. Low converter subvarieties of the above, even if not specifically identified herein, are also contemplated. In one embodiment, the cultivar is AA37 which is generally understood to be a cross between a South American dark tobacco and American Burley germplasm. Embodiments are also directed to compositions and methods for producing plants that have been modified to modulate (total) alkaloid and optionally nitrate levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant. Levels of TSNAs – such as NAB, NNK, NAT and NNN can also be modulated. Advantageously, the plants that are obtained may be similar or substantially the same in overall appearance to control plants. Various phenotypic characteristics such as degree of maturity, number of leaves per plant, stalk height, leaf insertion angle, leaf size (width and length), internode distance, and lamina-midrib ratio can be assessed by field observations. One aspect relates to a seed of a tobacco plant described herein. A further aspect relates to pollen or an ovule of a plant that is described herein. Also provided is a tissue culture of regenerable cells of the plant as described herein, which culture regenerates plants capable of expressing all the morphological and physiological characteristics of the parent. The regenerable cells include cells from leaves, pollen, embryos, cotyledons, hypocotyls, roots, root tips, anthers, flowers and a part thereof, ovules, shoots, stems, stalks, pith and capsules or callus or protoplasts derived therefrom. One object is to provide plants or parts thereof that exhibit modulated (for example, reduced or decreased) levels of (total) alkaloid and optionally nitrate in the plant material, for example, in dried or cured leaves. Suitably, the plants or parts thereof exhibit modulated (for example, reduced or decreased) levels of (total) alkaloid and optionally nitrate as compared to a control plant. Levels of TSNAs – such as NAB, NNK, NAT and NNN - can also be modulated. Suitably, the plants or parts thereof have substantially the same total harvest biomass (indicated as fresh leaf biomass per plant) as the control plant. Suitably, the amounts of (total) alkaloids in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of (total) alkaloids in dried leaf from a control plant or part thereof. Suitably, the amount of nicotine in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of nicotine in dried leaf from a control plant or part thereof. Suitably, the amount of nicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40% or at least about 50% as compared to the amount of nicotine in dried leaf from a control plant or part thereof. Suitably, the amount of nicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 54% as compared to the amount of nicotine in dried leaf from a control plant or part thereof. Suitably, the amount of nornicotine in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of nornicotine in dried leaf from a control plant or part thereof. Suitably, the amount of nornicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50% or at least about 55% as compared to the amount of nornicotine in dried leaf from a control plant or part thereof. Suitably, the amount of nornicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 58% as compared to the amount of nicotine in dried leaf from a control plant or part thereof. Suitably, the amount of anatabine in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of anatabine in dried leaf from a control plant or part thereof. Suitably, the amount of anatabine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50% at least about 60%, at least about 70%, at least about 80%, or at least about 90% as compared to the amount of anatabine in dried leaf from a control plant or part thereof. Suitably, the amount of anatabine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 92% as compared to the amount of anatabine in dried leaf from a control plant or part thereof. Suitably, the amount of myosmine in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of anatabine in dried leaf from a control plant or part thereof. Suitably, the amount of myosmine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, or at least about 50% as compared to the amount of myosmine in dried leaf from a control plant or part thereof. Suitably, the amount of myosmine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 56% as compared to the amount of myosmine in dried leaf from a control plant or part thereof. Suitably, the amount of anabasine in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of anabasine in dried leaf from a control plant or part thereof. Suitably, the amount of anabasine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10% as compared to the amount of anabasine in dried leaf from a control plant or part thereof. Suitably, the amount of anabasine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 12.5% as compared to the amount of anabasine in dried leaf from a control plant or part thereof. In certain embodiments, the amount of nitrate in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of nitrate in dried leaf from a control plant or part thereof. In certain embodiments, the amount of nitrate in dried leaf from the plant or part thereof according to the present invention is unchanged as compared to the amount of nitrate in dried leaf from a control plant or part thereof. Optionally, the amount of nitrate in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, or at least about 50% as compared to the amount of nitrate in dried leaf from a control plant or part thereof. Optionally, the amount of nitrate in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 54% as compared to the amount of nitrate in dried leaf from a control plant or part thereof. Suitably, the amount of NNK in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of NNK in dried leaf from a control plant or part thereof. Suitably, the amount of NNK in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 55% as compared to the amount of NNK in dried leaf from a control plant or part thereof. Suitably, the amount of NNK in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 58 or 59% as compared to the amount of NNK in dried leaf from a control plant or part thereof. Suitably, the amount of NNN in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of NNN in dried leaf from a control plant or part thereof. Suitably, the amount of NNN in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 60% as compared to the amount of NNN in dried leaf from a control plant or part thereof. Suitably, the amount of NNN in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 63 or 64% as compared to the amount of NNN in dried leaf from a control plant or part thereof. Suitably, the amount of NAB in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of NAB in dried leaf from a control plant or part thereof. Suitably, the amount of NAB in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 80% as compared to the amount of NAB in dried leaf from a control plant or part thereof. Suitably, the amount of NAB in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 82% as compared to the amount of NAB in dried leaf from a control plant or part thereof. Suitably, the amount of NAT in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of NAT in dried leaf from a control plant or part thereof. Suitably, the amount of NAT in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 90% as compared to the amount of NAB in dried leaf from a control plant or part thereof. Suitably, the amount of NAT in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 95% as compared to the amount of NAB in dried leaf from a control plant or part thereof. Suitably, the amount of total alkaloid in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of total alkaloid in dried leaf from a control plant or part thereof. Suitably, the amount of total alkaloid in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 70% as compared to the amount of total alkaloid in dried leaf from a control plant or part thereof. Suitably, the amount of total alkaloid in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 72% as compared to the amount of total alkaloid in dried leaf from a control plant or part thereof. Suitably, the amount of nicotine, nornicotine, anatabine and myosmine in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of nicotine, nornicotine, anatabine and myosmine in dried leaf from a control plant or part thereof. More suitably, the amount of nicotine, nornicotine, anatabine, myosmine and optionally nitrate in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of nicotine, nornicotine, anatabine, myosmine and optionally nitrate in dried leaf from a control plant or part thereof. More suitably, the amount of nicotine, nornicotine, anatabine, myosmine, NNK, NNN, NAB and NAT and optionally nitrate in dried leaf from the plant or part thereof is decreased as compared to the amount of nicotine, nornicotine, anatabine, myosmine, NNK, NNN, NAB and NAT and optionally nitrate in dried leaf from a control plant or part thereof. More suitably, the amount of nicotine, nornicotine, anatabine, myosmine, NNK, NNN, NAB, NAT, total alkaloid and optionally nitrate in dried leaf from the plant or part thereof is decreased as compared to the amount of nicotine, nornicotine, anatabine, myosmine, NNK, NNN, NAB and NAT and optionally nitrate in dried leaf from a control plant or part thereof.Suitably, the amount of nicotine, nornicotine, anatabine, myosmine and anabasine in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of nicotine, nornicotine, anatabine, myosmine and anabasine in dried leaf from a control plant or part thereof. More suitably, the amount of nicotine, nornicotine, anatabine, myosmine, anabasine and optionally nitrate in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of nicotine, nornicotine, anatabine, myosmine and anabasine in dried leaf from a control plant or part thereof. More suitably, the amount of nicotine, nornicotine, anatabine, myosmine, anabasine, NNK, NNN, NAB and NAT and optionally nitrate in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of nicotine, nornicotine, anatabine, myosmine, anabasine, NNK, NNN, NAB and NAT and optionally nitrate in dried leaf from a control plant or part thereof. More suitably, the amount of nicotine, nornicotine, anatabine, myosmine, anabasine, NNK, NNN, NAB, NAT, total alkaloid and optionally nitrate in dried leaf from the plant or part thereof according to the present invention is decreased as compared to the amount of nicotine, nornicotine, anatabine, myosmine, anabasine, NNK, NNN, NAB, NAT, total alkaloid and optionally nitrate in dried leaf from a control plant or part thereof. Suitably, the amount of nicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40% or at least about 50% as compared to the amount of nicotine in dried leaf from a control plant or part thereof; and the amount of nornicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50% or at least about 55% as compared to the amount of nornicotine in dried leaf from a control plant or part thereof; and the amount of anatabine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50% at least about 60%, at least about 70%, at least about 80%, or at least about 90% as compared to the amount of anatabine in dried leaf from a control plant or part thereof; and the amount of myosmine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, or at least about 50% as compared to the amount of myosmine in dried leaf from a control plant or part thereof; optionally the amount of nitrate in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, or at least about 50% as compared to the amount of nitrate in dried leaf from a control plant or part thereof; and the amount of NNK in dried leaf from the plant or part thereof is decreased by at least about 55%, at least about 58% or at least about 59% as compared to the amount of NNK in dried leaf from a control plant or part thereof; and the amount of NNN in dried leaf from the plant or part thereof is decreased by at least about 60%, or at least about 63% or at least about 64% as compared to the amount of NNN in dried leaf from a control plant or part thereof; the amount of NAB in dried leaf from the plant or part thereof is decreased by at least about 80% or at least about 82% as compared to the amount of NAB in dried leaf from a control plant or part thereof; and the amount of NAT in dried leaf from the plant or part thereof is decreased by at least about 90% or at least about 95% as compared to the amount of NAB in dried leaf from a control plant or part thereof; and the amount of total alkaloid in dried leaf from the plant or part thereof is decreased by at least about 70%, or at least about 72% as compared to the amount of NNK in dried leaf from a control plant or part thereof. More suitably, the amount of nicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40% or at least about 50% as compared to the amount of nicotine in dried leaf from a control plant or part thereof; and the amount of nornicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50% or at least about 55% as compared to the amount of nornicotine in dried leaf from a control plant or part thereof; and the amount of anatabine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50% at least about 60%, at least about 70%, at least about 80%, or at least about 90% as compared to the amount of anatabine in dried leaf from a control plant or part thereof; and the amount of myosmine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, or at least about 50% as compared to the amount of myosmine in dried leaf from a control plant or part thereof; and the amount of anabasine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10% as compared to the amount of anabasine in dried leaf from a control plant or part thereof; and optionally the amount of nitrate in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 10%, at least about 20%, at least about 30%, at least about 40%, or at least about 50% as compared to the amount of nitrate in dried leaf from a control plant or part thereof; the amount of NNK in dried leaf from the plant or part thereof is decreased by at least about 55%, at least about 58% or at least about 59% as compared to the amount of NNK in dried leaf from a control plant or part thereof; and the amount of NNN in dried leaf from the plant or part thereof is decreased by at least about 60%, or at least about 63% or at least about 64% as compared to the amount of NNN in dried leaf from a control plant or part thereof; and the amount of NAB in dried leaf from the plant or part thereof is decreased by at least about 80% or at least about 82% as compared to the amount of NAB in dried leaf from a control plant or part thereof; the amount of NAT in dried leaf from the plant or part thereof is decreased by at least about 90% or at least about 95% as compared to the amount of NAB in dried leaf from a control plant or part thereof; and the amount of total alkaloid in dried leaf from the plant or part thereof is decreased by at least about 70%, or at least about 72% as compared to the amount of NNK in dried leaf from a control plant or part thereof. Suitably, the amount of nicotinein dried leaf from the plant or part thereof according to the present invention is decreased by at least about 54% as compared to the amount of nicotine in dried leaf from a control plant or part thereof; and the amount of nornicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 58% as compared to the amount of nicotine in dried leaf from a control plant or part thereof; and the amount of anatabine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 92% as compared to the amount of anatabine in dried leaf from a control plant or part thereof; and the amount of myosmine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 56% as compared to the amount of myosmine in dried leaf from a control plant or part thereof; and optionally the amount of nitrate in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 54% as compared to the amount of nitrate in dried leaf from a control plant or part thereof; and the amount of NNK in dried leaf from the plant or part thereof is decreased by at least about 55%, at least about 58% or at least about 59% as compared to the amount of NNK in dried leaf from a control plant or part thereof; and the amount of NNN in dried leaf from the plant or part thereof is decreased by at least about 60%, or at least about 63% or at least about 64% as compared to the amount of NNN in dried leaf from a control plant or part thereof; and the amount of NAB in dried leaf from the plant or part thereof is decreased by at least about 80% or at least about 82% as compared to the amount of NAB in dried leaf from a control plant or part thereof; and the amount of NAT in dried leaf from the plant or part thereof is decreased by at least about 90% or at least about 95% as compared to the amount of NAB in dried leaf from a control plant or part thereof; and the amount of total alkaloid in dried leaf from the plant or part thereof is decreased by at least about 70%, or at least about 72% as compared to the amount of NNK in dried leaf from a control plant or part thereof. Suitably, the amount of nicotinein dried leaf from the plant or part thereof according to the present invention is decreased by at least about 54% as compared to the amount of nicotine in dried leaf from a control plant or part thereof; and the amount of nornicotine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 58% as compared to the amount of nicotine in dried leaf from a control plant or part thereof; and the amount of anatabine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 92% as compared to the amount of anatabine in dried leaf from a control plant or part thereof; and the amount of myosmine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 56% as compared to the amount of myosmine in dried leaf from a control plant or part thereof; and the amount of anabasine in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 12.5% as compared to the amount of anabasine in dried leaf from a control plant or part thereof; and optionally the amount of nitrate in dried leaf from the plant or part thereof according to the present invention is decreased by at least about 54% as compared to the amount of nitrate in dried leaf from a control plant or part thereof; and the amount of NNK in dried leaf from the plant or part thereof is decreased by at least about 55%, at least about 58% or at least about 59% as compared to the amount of NNK in dried leaf from a control plant or part thereof; and the amount of NNN in dried leaf from the plant or part thereof is decreased by at least about 60%, or at least about 63% or at least about 64% as compared to the amount of NNN in dried leaf from a control plant or part thereof; and the amount of NAB in dried leaf from the plant or part thereof is decreased by at least about 80% or at least about 82% as compared to the amount of NAB in dried leaf from a control plant or part thereof; and the amount of NAT in dried leaf from the plant or part thereof is decreased by at least about 90% or at least about 95% as compared to the amount of NAB in dried leaf from a control plant or part thereof; and the amount of total alkaloid in dried leaf from the plant or part thereof is decreased by at least about 70%, or at least about 72% as compared to the amount of NNK in dried leaf from a control plant or part thereof.Embodiments are also directed to compositions and methods for producing the plants or plant cells that are described herein. An increase in function or activity as compared to a control may be from about 5 % to about 100 %, or an increase of at least 10 %, at least 20 %, at least 25 %, at least 30 %, at least 40 %, at least 50 %, at least 60 %, at least 70 %, at least 75 %, at least 80 %, at least 90 %, at least 95 %, at least 98 %, or 100 % or more - such as 200%, 300%, 500%, 1000% or more. A decrease in function or activity as compared to a control may be from about 5 % to about 100 %, or a decrease of at least 10 %, at least 20 %, at least 25 %, at least 30 %, at least 40 %, at least 50 %, at least 60 %, at least 70 %, at least 75 %, at least 80 %, at least 90 %, at least 95 %, at least 98 %, or 100 %. A plant carrying the mutation described herein in a QS polynucleotide can be used in a plant breeding program to create useful lines, varieties and hybrids. In particular, the mutant can be introgressed into the commercially important varieties described above. Thus, methods for breeding plants are provided, that comprise crossing plant as described herein with a plant comprising a different genetic identity. The method may further comprise crossing the progeny plant with another plant, and optionally repeating the crossing until a progeny with the desirable genetic traits or genetic background is obtained. One purpose served by such breeding methods is to introduce a desirable genetic trait into other varieties, breeding lines, hybrids or cultivars, particularly those that are of commercial interest. Another purpose is to facilitate stacking of genetic modifications of different genes in a single plant variety, lines, hybrids or cultivars. Intraspecific as well as interspecific matings are contemplated. The progeny plants that arise from such crosses, also referred to as breeding lines, are examples of plants of the disclosure. In one embodiment, a method is provided for producing a plant comprising: (a) crossing a plant of the present disclosure with a second plant to yield progeny tobacco seed; (b) growing the progeny tobacco seed, under plant growth conditions, to yield a non-naturally occurring plant. The method may further comprise: (c) crossing the previous generation of non-naturally occurring plant with itself or another plant to yield progeny tobacco seed; (d) growing the progeny tobacco seed of step (c) under plant growth conditions, to yield additional non-naturally occurring plants; and (e) repeating the crossing and growing steps of (c) and (d) multiple times to generate further generations of non-naturally occurring plants. The method may optionally comprises prior to step (a), a step of providing a parent plant which comprises a genetic identity that is characterized and that is not identical to the plant of the present disclosure. In some embodiments, depending on the breeding program, the crossing and growing steps are repeated from 0 to 2 times, from 0 to 3 times, from 0 to 4 times, 0 to 5 times, from 0 to 6 times, from 0 to 7 times, from 0 to 8 times, from 0 to 9 times or from 0 to 10 times, in order to generate generations of non-naturally occurring plants. Backcrossing is an example of such a method wherein a progeny is crossed with one of its parents or another plant genetically similar to its parent, in order to obtain a progeny plant in the next generation that has a genetic identity which is closer to that of one of the parents. Techniques for plant breeding, particularly plant breeding, are well known and can be used in the methods of the disclosure. Certain embodiments exclude the step of selecting a plant. According to the disclosure, in a breeding program, successful crosses yield F1 plants that are fertile. Selected F1 plants can be crossed with one of the parents, and the first backcross generation plants are self-pollinated to produce a population that is again screened for variant gene expression (for example, the null version of the gene). The process of backcrossing, self-pollination, and screening is repeated, for example, at least 4 times until the final screening produces a plant that is fertile and reasonably similar to the recurrent parent. This plant, if desired, is self-pollinated and the progeny are subsequently screened again to confirm that the plant exhibits variant gene expression. In some embodiments, a plant population in the F2 generation is screened for variant gene expression, for example, a plant is identified that fails to express a polypeptide due to the absence of the gene according to standard methods, for example, by using a PCR method with primers based upon the polynucleotide sequence information for the polynucleotide(s) described herein (or any combination thereof as described herein). Aside from the mutation described herein, the plants or plant cells described herein can have one or more further mutations either in the same polynucleotides or polypeptides as described herein or in one or more other polynucleotides or polypeptides within the genome. One or more further genetic modifications (for example, mutations) can be present in the plants and parts thereof. Parts of the plants described herein, particularly the leaf lamina and midrib of such plants, can be incorporated into or used in making various consumable products including but not limited to aerosol forming materials, aerosol forming devices, smoking articles, smokable articles, smokeless products, medicinal or cosmetic products, intravenous preparations, tablets, powders, and tobacco products. Examples of aerosol forming materials include tobacco compositions, tobaccos, tobacco extract, cut tobacco, cut filler, cured tobacco, expanded tobacco, homogenized tobacco, reconstituted tobacco, and pipe tobaccos. Smoking articles and smokable articles are types of aerosol forming devices. Examples of smoking articles or smokable articles include cigarettes, cigarillos, and cigars. Examples of smokeless products comprise chewing tobaccos, and snuffs. In certain aerosol forming devices, rather than combustion, a tobacco composition or another aerosol forming material is heated by one or more electrical heating elements to produce an aerosol. In another type of heated aerosol forming device, an aerosol is produced by the transfer of heat from a combustible fuel element or heat source to a physically separate aerosol forming material, which may be located within, around or downstream of the heat source. Smokeless tobacco products and various tobacco-containing aerosol forming materials may contain tobacco in any form, including as dried particles, shreds, granules, powders, or a slurry, deposited on, mixed in, surrounded by, or otherwise combined with other ingredients in any format, such as flakes, films, tabs, foams, or beads. As used herein, the term ‘smoke’ is used to describe a type of aerosol that is produced by smoking articles, such as cigarettes, or by combusting an aerosol forming material. In one embodiment, there is also provided cured plant material from the plants described herein. Processes of curing green tobacco leaves are known by those having skills in the art and include without limitation air-curing, fire-curing, flue-curing and sun-curing as described herein. In another embodiment, there is described tobacco products including tobacco-containing aerosol forming materials comprising plant material – such as leaves, suitably cured leaves - from the tobacco plants described herein. The tobacco products described herein can be a blended tobacco product which may further comprise unmodified tobacco. The plants may have other uses in, for example, agriculture. For example, plants described herein can be used to make animal feed and human food products. The disclosure also provides methods for producing seeds comprising cultivating the plant described herein, and collecting seeds from the cultivated plants. Seeds from plants described herein can be conditioned and bagged in packaging material by means known in the art to form an article of manufacture. Packaging material such as paper and cloth are well known in the art. A package of seed can have a label, for example, a tag or label secured to the packaging material, a label printed on the package that describes the nature of the seeds therein. Compositions, methods and kits for genotyping plants for identification, selection, or breeding can comprise a means of detecting the presence of a polynucleotide (or any combination thereof as described herein) in a sample of polynucleotide. Accordingly, a composition is described comprising one or more primers for specifically amplifying at least a portion of one or more of the polynucleotides and optionally one or more probes and optionally one or more reagents for conducting the amplification or detection. Accordingly, gene specific oligonucleotide primers or probes comprising about 10 or more contiguous polynucleotides corresponding to the polynucleotide(s) described herein are disclosed. Said primers or probes may comprise or consist of about 15, 20, 25, 30, 40, 45 or 50 more contiguous polynucleotides that hybridise (for example, specifically hybridise) to the polynucleotide(s) described herein. In a further aspect, there is also provided a method of detecting a QS polynucleotide(s) described herein (or any combination thereof as described herein) in a sample comprising the step of: (a) providing a sample comprising, or suspected of comprising, a polynucleotide; (b) contacting said sample with one or more primers or one or more probes for specifically detecting at least a portion of the polynucleotide(s); and (c) detecting the presence of an amplification product, wherein the presence of an amplification product is indicative of the presence of the polynucleotide(s) in the sample. In a further aspect, there is also provided the use of one or more primers or probes for specifically detecting at least a portion of the polynucleotide(s). Kits for detecting at least a portion of the polynucleotide(s) are also provided which comprise one or more primers or probes for specifically detecting at least a portion of the polynucleotide(s). The kit may comprise reagents for polynucleotide amplification - such as PCR - or reagents for probe hybridization-detection technology - such as Southern Blots, Northern Blots, in-situ hybridization, or microarray. The kit may comprise reagents for antibody binding-detection technology such as Western Blots, ELISAs, SELDI mass spectrometry or test strips. The kit may comprise reagents for DNA sequencing. The kit may comprise reagents and instructions for using the kit. In some embodiments, a kit may comprise instructions for one or more of the methods described. The kits described may be useful for genetic identity determination, phylogenetic studies, genotyping, haplotyping, pedigree analysis or plant breeding particularly with co- dominant scoring. The present disclosure also provides a method of genotyping a plant, a plant cell or plant material comprising a polynucleotide as described herein. Genotyping provides a means of distinguishing homologs of a chromosome pair and can be used to differentiate segregants in a plant population. Molecular marker methods can be used for phylogenetic studies, characterizing genetic relationships among crop varieties, identifying crosses or somatic hybrids, localizing chromosomal segments affecting monogenic traits, map based cloning, and the study of quantitative inheritance. The specific method of genotyping may employ any number of molecular marker analytic techniques including amplification fragment length polymorphisms (AFLPs). AFLPs are the product of allelic differences between amplification fragments caused by polynucleotide variability. Thus, the present disclosure further provides a means to follow segregation of one or more genes or polynucleotides as well as chromosomal sequences genetically linked to these genes or polynucleotides using such techniques as AFLP analysis. The Nicotiana tabacum may be propagatable or non-propagatable. The Nicotiana tabacum may not be obtained exclusively by an essentially biological process. The process may not consist exclusively of entirely natural phenomena - such as crossing or selection. The genome of the Nicotiana tabacum can be purposefully (genetically) modified or engineered. The Nicotiana tabacum described herein may be obtained by techniques which differ from conventional breeding techniques in that they work primarily through the purposeful insertion and / or modification of one or more genes or polynucleotides or polypeptides in a plant. The invention is further described in the Examples below, which are provided to describe the invention in further detail. These examples, which set forth a preferred mode presently contemplated for carrying out the invention, are intended to illustrate and not to limit the invention. EXAMPLE Example 1 - Identification of NtQS-T C133Y mutant Through a field screening for low alkaloid levels performed under high nitrate fertilisation conditions, a single tobacco mutant line (AA37) is identified. Through a QTL-like approach, a variant exhibiting a recessive mutation is identified. A guanine nucleotide in the wild-type plant is replaced by an adenine in the mutant, within the sequence gtaccgggttg / acactacacag (mutation site indicated in bold) belonging to the T form of the QS gene (Ntab-TN90_AYMY-SS91625) located on the tobacco chromosome 4. This specific mutation leads to a change in an amino acid: cysteine (Cys or C) in position 133 becomes a tyrosine (Tyr or Y). Example 2 - Methods for alkaloid and nitrate measurement Samples for UHPLC-MS alkaloid analysis are prepared by extracting approximately 25 mg of fine powder with water / methanol (3:7 ratio, with 500 ng mL-1 quinoline as internal standard; 5 mL) by agitating on a rotary shaker for 48 hours, filtering (Fisherbrand™ Sterile PES Syringe Filter with pore size of 0.2 pm), and diluting 1:50 with the extraction mixture. A simultaneous determination of alkaloids is performed on an Ultimate 3000 UHPLC system coupled to a Q-Exactive mass spectrometer (Thermo Fisher Scientific, Waltham, MA USA). Chromatographic separation is performed on an Acquity HSS T3 column (1.7 pm; 100 x 2.1 mm; Waters, Milford, MA USA); the column temperature is set to 45°C. Eluents are ammonium acetate in water (10 mM; pH = 8.9; eluent A) and ammonium acetate in methanol (10 mM; eluent B) applied as a gradient (0 min, 10% B; 0.25 min, 10% B; 4.25 min, 98% B; 5.25 min, 98% B; flow: 0.5 mL min-1). The injection volume is 5 pL. Nicotine, anabasine, myosmine, nornicotine and anatabine, elute after 3.89, 3.27, 3.47, 2.76, 3.36 min, respectively, and are detected as [M + H]+ pseudomolecular ions after positive electrospray ionization. Nitrate analysis is according to the CORESTA recommended method No. 36 for determination of nitrate in tobacco and smokeless tobacco products by reduction to nitrite and continuous flow analysis. Quantification of NAB, NNK, NAT and NNN were conducted in accordance with "Method 1" of Morgan et al. (Beit. Tabakforschung 23:192-203 (2004)). Methods for total alkaloid analysis in tobacco are reported in the CORESTA recommended method No.35. Example 3 - Analysis of NtQS-T C133Y mutant grown under hydroponic conditions The AA37 mutant plant is crossed (F1) with Burley TN90 (AA37xTN90) and F2 plantlets are grown under hydroponic conditions in a greenhouse environment. The leaves are collected in young growing plants of AA37xTN90 tobacco NtQS-T C133Y homozygous mutants and dried. The CORESTA recommendation for tobacco curing is described in CORESTA Guide N°17, April 2016, Sustainability in Leaf Tobacco Production. The alkaloid analyses shows a decrease compared to their outsegregant wild types. More specifically, a statistically significant decrease of nicotine (-54%, p value=0.003337), decrease of nornicotine (-58%, p value=0.003855), decrease of anatabine (-92%, p value=0.001953) and decrease of myosmine (-56%, p value=0.073082) is observed in the NtQS-T C133Y mutant compared to the wild type. Anabasine levels are also decreased in the NtQS-T C133Y mutant, but the reduced statistical power of the experiments (n=5 lines) did not allow a robust conclusion for this specific alkaloid (-12.5%, p value=0.123206). Surprisingly, NtQS-T C133Y mutant lines also demonstrated decreased nitrate levels compared to outsegregant wild type lines (-54%, p value=0.002993). Alkaloid and nitrate values are reported in Table 1, together with standard deviations and P values calculated in a two-tailed t student test. Example 4 - Analysis of NtQS-T C133Y mutant grown under field conditions Tobacco-Specific Nitrosamine (TSNA) and nitrate values for the mutant and wild type plants grown under field conditions are reported in Table 2. Plants are grown according to standard good agricultural practices for Burley tobacco (according to Grandes cultures fiches techniques, agridea - developpement de l’agriculture et de l’espace rural, www.agridea.ch). The leaves are collected in plants of AA37xTN90 tobacco NtQS-T C133Y homozygous mutants and dried, as described above. The field conditions confirmed the low total alkaloid phenotype for the mutant plant and indicated lower NNK (about 58.8% reduction as compared to the wild-type), lower NNN (about 63.6% reduction as compared to the wild- type), lower NAB (about 82% reduction as compared to the wild-type) and lower NAT (about 95.1.% reduction as compared to the wild-type) levels for the mutant plant. Nitrate levels did not significantly decrease under field conditions. Further aspects of the present invention are set forth in the following numbered paragraphs: 1. A Nicotiana tabacum plant or part thereof comprising: (a) a mutated polynucleotide sequence encoding a Nicotiana tabacum quinolinate synthase (NtQS-T) polypeptide comprising a contiguous polypeptide sequence of SEQ ID NO: 3 and comprising at least one mutation therein that modulates alkaloid and nitrate levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant; (b) a mutated polypeptide sequence encoded by the polynucleotide sequence set forth in (a); or (c) a construct, vector or expression vector comprising the mutated polynucleotide sequence set forth in (a). 2. The Nicotiana tabacum plant or part thereof according to paragraph 1, wherein the cysteine at amino acid position 133 of NtQS-T is substituted in the mutated polypeptide. 3. The Nicotiana tabacum plant or part thereof according to paragraph 2, wherein the cysteine at amino acid position 133 of NtQS-T is substituted for an aromatic amino acid selected from the group consisting of histidine, phenylalaine, tryptophan, asparagine and tyrosine. 4. The Nicotiana tabacum plant or part thereof according to paragraph 2, wherein the cysteine at amino acid position 133 of NtQS-T is substituted for tyrosine (C133Y) in the mutated polypeptide. 5. The Nicotiana tabacum plant or part thereof according to paragraph 4, wherein the mutated polypeptide comprises the contiguous polypeptide sequence of SEQ ID NO: 5; or wherein the mutated polypeptide consists of the contiguous polypeptide sequence of SEQ ID NO: 5. 6. The Nicotiana tabacum plant or part thereof according to any of the preceding paragraphs, wherein the mutated polynucleotide sequence comprises, consists or consists essentially of the polynucleotide sequence set forth in SEQ ID NO: 4. 7. The Nicotiana tabacum plant or part thereof according to any of the preceding paragraphs, wherein the alkaloids are nicotine, nornicotine, anatabine and myosmine, suitably, wherein the alkaloids are nicotine, nornicotine, anatabine, myosmine and anabasine. 8. The Nicotiana tabacum plant or part thereof according to any of the preceding paragraphs, wherein the at least one mutation reduces alkaloid and nitrate levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant. 9. Nicotiana tabacum plant material, cured plant material, or homogenized plant material obtained from the Nicotiana tabacum plant or part thereof according to any of paragraphs 1 to 8. 10. A method for preparing a Nicotiana tabacum plant or part thereof having modulated alkaloid and nitrate levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant comprising: (a) providing a Nicotiana tabacum plant; (b) introducing into the Nicotiana tabacum plant one or more mutations in a quinolinate synthase (NtQS-T) polypeptide comprising or consisting of a contiguous polypeptide sequence of SEQ ID NO: 3; (c) determining if the one or more mutations modulate alkaloid and nitrate levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant; and (d) identifying a Nicotiana tabacum plant or part thereof comprising one or more mutations in NtQS-T that modulate alkaloid and nitrate levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant. 11. A method for producing cured Nicotiana tabacum plant material with an altered amount of alkaloid and nitrate as compared to control plant material, comprising: providing the Nicotiana tabacum plant or part thereof according to any of paragraphs 1 to 8 or the plant material according to paragraph 9; (b) harvesting the Nicotiana tabacum plant or part thereof or Nicotiana tabacum plant material; and (c) curing the harvested Nicotiana tabacum plant or the harvested Nicotiana tabacum plant material. 12. The method according to paragraph 11, wherein the plant material is leaf and the curing method is selected from the group consisting of air curing, fire curing, smoke curing, and flue curing. 13. A cured or dried leaf obtained from the Nicotiana tabacum plant or part thereof according to any of paragraphs 1 to 8 or obtained by the method of paragraph 11 or 12. 14. The cured or dried leaf according to paragraph 13, wherein the leaves are air-cured or sun-cured or flue-cured or fermented. 15. A tobacco product comprising the Nicotiana tabacum plant or part thereof of any of paragraphs 1 to 8, the plant material according to paragraph 9 or the cured or dried leaf according to paragraph 13 or paragraph 14. Any publication cited or described herein provides relevant information disclosed prior to the filing date of the present application. Statements herein are not to be construed as an admission that the inventors are not entitled to antedate such disclosures. All publications mentioned in the above specification are herein incorporated by reference. Various modifications and variations of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in cellular, molecular and plant biology or related fields are intended to be within the scope of the claims.

[0002] SEQUENCE LISTING SEQ ID NO: 1 – genomic sequence of NtQS-T wild type gggagcacacgttttctctacattaaacaattgatgcacacacctctctaactcagaattccacaacataatttc attcttgctccccaaagcacattatatataatcacacaacacataagcatagacactaagagctgagagatagca gcagaaaaggtcttcgattccagcacttttctaaagtttctttggagcttctaatattactgaagagcttttttc tactaaaggtccatttcctcttctttacttttccgatattggttcatattatgcttcactgtgatctttgagttt ttttctgtgttcgtttgcttaatattgtttcatcatagtttactgtttctttcgattaaccatagattagacttg aaagaaatctgggtctaatttggattgaaattagttaaagagaaattgggctgtgaacagagttgggctcctttt taatcaaatgtcaggtccaatagtttcagtatttatttggaataccaaagcttaattccaattgaggttttgacc atcaaaacttaagcagattttaaaaaacaaattacttattgtcaatataataatttatataatttttgtgctgac cattttcgcgggtgattataggtggccatcgtcggaatttcaatttgctaccattaatttgcaaggccctcctcc tcccgttccctttgtcctctcctctctcttctgcacatccaaatccaacttccctaccgccattttccgcacttc gataactcgttaacccctcagtctctaatttcttcctcacccccaaaaaaaaaaaactttcatttctctgtcttc tttccaaacttttttcttcctcccctgcttacacacaagaatctgtgatggatgccgcaaatttagtcatgaaat cttccttgttttcgaaatccccatgtcccctttttagttctaaactcattcctagagcaccaccctctgtcttta ctctgccttctacctttagacccctcgttaaatgcatacaagcttcattcccaccaaaccctgattccaaaaaac cctcaaacaattcaacctttacgtgttcagctgtgacttccttcccttctcaacaatctcagcctcacgcgcctt ccgatgccaagctccaactcctgatctctgaattccagtccctcgtcgaaccaatggaccgcgtgaaacgcctct tgcactactccacactcctccctccaatggacgcgtccttcaaaacccctgagaatcgcgtaccgggttgcacta cacaggtatggctgaacgtgagtttcgatgaggctgagaacaggatgaaatttttggcggacagtgactcggaaa taactaaagggttttgcgcgtgtttggtttcgctgctggacggggctactcccgatgaggtgctggcgttgaaaa cggaggacttgaatgctttgaatgttgcggggttgaacgggaaaggatcggcatctagggcgaatacgtggcata atgtgttggtcagcatgcagaaaaggacaagggccttagttgcggagcgtgaaggcaggccgcgcggcgagctct ttccatctctagtaatcacagctgatggtatccaaccccaaggcagctacgctgaagcccaggtactctttcttc tttacttgaacattttaggcatttaggaaatgcttgttcatcatttgttttgtgtcctagattactgtttaccgt ttgttgttatcttcaatttagttaggatccatacatattctaggcacaatctgaaaatatagctcatttatgttt atagggcaaggagaaaagagagattcacattatggcaaaaaggaaagaaagatacacgtttagtattagtgaggc ttgaacttcctgacatttaaagtcctaagttagtttctattgtaattgcaggcaaggttcctgtttcctgatgaa tcaagggtccaaaaacttgccagtttgctaaaggagaagaaaataggagttgttgctcatttctacatggaccct gaggtgcaaggtgttctaactgcagcgcagaagctttggccccatatacatatatctgattctttagtcatggct gataaagctgtcagtatggcaaaagctggatgtgaatatatatctgtattgggtgtagatttcatgtcagagaat gtgcgagccattcttgatctagctggattcccagaggtagacacatcccccgtttttgtgttctattatatgagt gctttgtagtgatgacctgacttctaagttagtccgtgtttgcttggtcaaccagttgggagtaccattctaatt gatttcctcgtgctagacaatgtgcaaaatttacaaagaaaaccctaagtttttctgcatatgatatacacaata ttaaaagagcagcagggaacagtttcttccgctgatagatgcacaatgaattgtcacatgttaagttctctgttt accgctcaattggattcctacttggaaattttccatctggctgttttcctgtgaaataatcccctatgttgttga tctttgttgaacctaaggtatacttggttgataggtatcttctgctttatacaggtccagttttctgctatgaaa atgaaatcttttctgtatattaccaatttcattgtgcacatgagtttatcttcaagggtaaatggtctanttaat gaatctgaagcgcatttgtaggtgaatttggcaactcaaatctatttccactcaaatacccttgatatccccctc tacctgtagatgtagaatgcttcccccctcaggcggaacgaaattaacagaaggagaagttaatgaacaccaaaa ataaacactggttgcttgttatattttttatttgtatctttaaggcttgatctctgctgaacattccatttaact gaacgtcttaatttagtaacatttatgagcttagtttaaagtgcactgtggcaacaaaataggtaaaatagcaag agcaagtcaatgtatgaagcttccaagcctttgagatttgccatgttattttgggactatgctctttttggatat tgatagtttaatggattatatctatttacataacttgacaggcaggtgcaagtatgccgtctctaatatattctg catgtattaatacttctttttgtaggttggagtttatcggatgtcggacgaacgcattggttgttctttggctga tgctgcagccagcccagcatacttggattatcttaaaacagcttcaacttcttctccatctctgcatgttgtgta cataaatacttcactggagacaaaagcatattctcatgagcttgttccgactataacatgtacttcctctaatgt tgtgcaaactattctgcaggtttgttggttatttccattgatttagtttttttttttcaagttcttcataattca tcttttgtcttttcaatgattaaatatcagtatatcttcttcaactaatgaagctgcatctaatatcgatccagg catttgctgaagtacctgacttggaagtgttgtatggtcctgatacctacatgggttcaaacattgcggaattgt tcacccagatgtccacgatgactgatgaagaaatttctgcgatacatcctttgcacaacagaatctccattaaat ctttgcttcctcgactgcattattttcaggtaattctgagttttttacactcatggaaatgaaggaggtcttaat ggccattctttactgtaatttaatttgaagcattggtcaagcggaagctttgaggaaaggactgatctcctcaaa gctttatctgagaaccatcaataatgcttcaatttgctgtatgatattgttcaggtctgctatcccccgtcatca ttttaattaataaataacctttgtctcctttgcttttcccctccaggatgggacatgtattgttcatcacctctt tggtcatgaagttgtggagaagataaatgaaatgtatggggatgcattccttactgcacactttgaagttcctgg tgaaatgttttccctggcaatggaagcgaagaaaaggggcatgggagtagtaggttctacctcgaacatactcga ctttatcaaagaaagggtagaagagtccttgaatagaaacgtagatgaacatcttcagtttgttttgggaacgga atcaggaatgattacggcaatagttgcagcagtcggtaaattactaggttctgctgactcctcttccggtggagc aaaagtaagtgttgagattgtctttcctgtctcgtcagaatcagtgacaagaacatctacgggttcgcctctgga ccaaaataaggtcaatattatacctggagttgcaagtggagaggggtgttctctacatggtggatgtgcctcctg tccatatatgaaggttagcattatttgtctgtcatctattgcctgcttctttttttctttgtactgactaattct ctcagttcctagctgttacggtttggtatttgccaaaaataaactaaacataagtgttgtttgttttcttccata tcactcatattcttagtgcatattagagaagaattctgtcaacaatctttgtatcctattgcctgtgtatgtaag gggagtgcattatggggattggcggatgcgccatattcgacctgcttggaaaaaatgttcataggggattgtgaa ggcagagagtattggtcaagaaatgttctttcaatggttgaatgcataccttcatattctcctgtttttcattgt gaagtgataggtctagcgcggcttaggaatcctcgtgccactctcccgatttcagaacttcattctcatttgtca ctccccacgcttgaaccgaaaaaaaatcttcacgtttctttttcaattattttttagctaccatgcaaatcatat gtggacttaaatgaaataactttggctagaatgtaaatgcagggcggtcatgttacccttttcatgtgttttgtg gagttaagtgaataagctgtagccctggcatgataatggtttccgatctttctatagatggttgctccaaatagg tgccttgatgtacggtctaatgaggctactatgaaatatttactcatggatggggcaagctcttctattctggtt catgttgcattgttgacatagaatgacttattgctacatgttatgctgtttcaaatgttgcattgttgacataga ataacttactgctacattttacacttcaacttcataagtgcagttttgtagtggatgtcttcctggaccatatag aacctattacttttctaaagatggattctcatttgcttacatcctttatctgtcagatgaactctcttagctcgt tgctaaaagtttgccagagcttgccccatggcaaagccgaactttcagcttatgaggcaggacgattcagtttgc gaacccccaagggaaaacaaattgcggatgttggttgtgagccggttctgcacatgagacactttcaggtttgtt tcctcattttctgtattagcaaaatgagtgtatccatgtaacttgacaatcctaatgttgcccaagtcatgattt gaaaaactgcactgagcatgtgatagggacattcagttagatatcgacttttgagtgttttctttttgaaccccc tttgtgcaggcaacaaagagattaccagagcagctaatcaatcaaatacttcaacctcgtgataatggacgatca agctctgcttaaacaagacgaaagctagacagacagtggtatttactcgagacaaataaaagtttacttcccttc accatacttggcaagggaaggcctagaggagcattatgccagcctcattttttctgcataggacatggattatac aggaattttatgctgtgcacatgctttggttgttccgtttcttacctttctttttatttttacctggtttaagtg tgattgtaatagatggaggaaaataatggttgtacttttgtttcccctacaaaatattgaaggtgtttgtattcg ttatgcttaaataagctttaaagctcttttagttttgttcttttttagtgtttggcaatattgtcaaatttattt tggttgaccaatcattttatatttgtatcccttttaacttttcgtaatcccaacattaccct SEQ ID NO: 2 – transcript of NtQS-T wild type; site of polynucleotide to be mutated is indicated gggagcacacgttttctctacattaaacaattgatgcacacacctctctaactcagaattccacaacataatttc attcttgctccccaaagcacattatatataatcacacaacacataagcatagacactaagagctgagagatagca gcagaaaaggtcttcgattccacttctaatattactgaagagcttttttctactaaaggtggccatcgtcggaat ttcaatttgctaccattaatttgcaaggccctcctcctcccgttccctttgtcctctcctctctcttctgcacat ccaaatccaacttccctaccgccattttccgcacttcgataactcgttaacccctcagtctctaatttcttcctc accccaaaaaaaaaaaaactttcatttctctgtcttctttccaaacttttttcttcctcccctgcttacacacaa gaatctgtgatggatgccgcaaatttagtcatgaaatcttccttgttttcgaaatccccatgtcccctttttagt tctaaactcattcctagagcaccaccctctgtctttactctgccttctacctttagacccctcgttaaatgcata caagcttcattcccaccaaaccctgattccaaaaaaccctcaaacaattcaacctttacgtgttcagctgtgact tccttcccttctcaacaatctcagcctcacgcgccttccgatgccaagctccaactcctgatctctgaattccag tccctcgtcgaaccaatggaccgcgtgaaacgcctcttgcactactccacactcctccctccaatggacgcgtcc ttcaaaacccctgagaatcgcgtaccgggttgcactacacaggtatggctgaacgtgagtttcgatgaggctgag aacaggatgaaatttttggcggacagtgactcggaaataactaaagggttttgcgcgtgtttggtttcgctgctg gacggggctactcccgatgaggtgctggcgttgaaaacggaggacttgaatgctttgaatgttgcggggttgaac gggaaaggatcggcatctagggcgaatacgtggcataatgtgttggtcagcatgcagaaaaggacaagggcctta gttgcggagcgtgaaggcaggccgcgcggcgagctctttccatctctagtaatcacagctgatggtatccaaccc caaggcagctacgctgaagcccaggcaaggttcctgtttcctgatgaatcaagggtccaaaaacttgccaatttg ctaaaggagaagaaaataggagttgttgctcatttctacatggaccctgaggtgcaaggtgttctaactgcagcg cagaagctttggccccatatacatatatctgattctttagtcatggctgataaagctgtcagtatggcaaaagct ggatgtgaatatatatctgtattgggtgtagatttcatgtcagagaatgtgcgagccattcttgatctagctgga ttcccagaggttggagtttatcggatgtcggacgaacgcattggttgttctttggctgatgctgcagccagccca gcatacttggattatcttaaaacagcttcaacttcttctccatctctgcatgttgtgtacataaatacttcactg gagacaaaagcatattctcatgagcttgttccgactataacatgtacttcctctaatgttgtgcaaactattctg caggcatttgctgaagtacctgacttggaagtgttgtatggtcctgatacctacatgggttcaaacattgcggaa ttgttcacccagatgtccacgatgactgatgaagaaatttctgcgatacatcctttgcacaacagaatctccatt aaatctttgcttcctcgactgcattattttcaggatgggacatgtattgttcatcacctctttggtcatgaagtt gtggagaagataaatgaaatgtatggggatgcattccttactgcacactttgaagttcctggtgaaatgttttcc ctggcaatggaagcgaagaaaaggggcatgggagtagtaggttctacctcgaacatactcgactttatcaaagaa agggtagaagagtccttgaatagaaacgtagatgaacatcttcagtttgttttgggaacggaatcaggaatgatt acggcaatagttgcagcagtcggtaaattactaggttctgctgactcctcttccggtggagcaaaagtaagtgtt gagattgtctttcctgtctcgtcagaatcagtgacaagaacatctacgggttcgcctctggaccaaaataaggtc aatattatacctggagttgcaagtggagaggggtgttctctacatggtggatgtgcctcctgtccatatatgaag atgaactctcttagctcgttgctaaaagtttgccagagcttgccccatggcaaagccgaactttcagcttatgag gcaggacgattcagtttgcgaacccccaagggaaaacaaattgcggatgttggttgtgagccggttctgcacatg agacactttcaggcaacaaagagattaccagagcagctaatcaatcaaatacttcaacctcgtgataatggacga tcaagctctgcttaaacaagacgaaagctagacagacagtggtatttactcgagacaaataaaagtttacttccc ttcaccatacttggcaagggaaggcctagaggagcattatgccagcctcattttttctgcataggacatggatta tacaggaattttatgctgtgcacatgctttggttgttccgtttcttacctttctttttatttttacctggtttaa gtgtgattgtaatagatggaggaaaataatggttgtacttttgtttcccctacaaaatattgaaggtgtttgtat tcgttatgcttaaataagctttaaagctcttttagttttgttcttttttagtgtttggcaatattgtcaaattta ttttggttgaccaatcattttatatttgtatcccttttaacttttcgtaatcccaacattaccct SEQ ID NO: 3 - protein sequence of NtQS-T wild type; site of polypeptide to be mutated is indicated MDAANLVMKSSLFSKSPCPLFSSKLIPRAPPSVFTLPSTFRPLVKCIQASFPPNPDSKKPSNNSTFTCSAVTSFP SQQSQPHAPSDAKLQLLISEFQSLVEPMDRVKRLLHYSTLLPPMDASFKTPENRVPGCTTQVWLNVSFDEAENRM KFLADSDSEITKGFCACLVSLLDGATPDEVLALKTEDLNALNVAGLNGKGSASRANTWHNVLVSMQKRTRALVAE REGRPRGELFPSLVITADGIQPQGSYAEAQARFLFPDESRVQKLANLLKEKKIGVVAHFYMDPEVQGVLTAAQKL WPHIHISDSLVMADKAVSMAKAGCEYISVLGVDFMSENVRAILDLAGFPEVGVYRMSDERIGCSLADAAASPAYL DYLKTASTSSPSLHVVYINTSLETKAYSHELVPTITCTSSNVVQTILQAFAEVPDLEVLYGPDTYMGSNIAELFT QMSTMTDEEISAIHPLHNRISIKSLLPRLHYFQDGTCIVHHLFGHEVVEKINEMYGDAFLTAHFEVPGEMFSLAM EAKKRGMGVVGSTSNILDFIKERVEESLNRNVDEHLQFVLGTESGMITAIVAAVGKLLGSADSSSGGAKVSVEIV FPVSSESVTRTSTGSPLDQNKVNIIPGVASGEGCSLHGGCASCPYMKMNSLSSLLKVCQSLPHGKAELSAYEAGR FSLRTPKGKQIADVGCEPVLHMRHFQATKRLPEQLINQILQPRDNGRSSSA* SEQ ID NO: 4 – transcript of NtQS-T C133Y mutant; polynucleotide mutation is indicated gggagcacacgttttctctacattaaacaattgatgcacacacctctctaactcagaattccacaacataatttc attcttgctccccaaagcacattatatataatcacacaacacataagcatagacactaagagctgagagatagca gcagaaaaggtcttcgattccacttctaatattactgaagagcttttttctactaaaggtggccatcgtcggaat ttcaatttgctaccattaatttgcaaggccctcctcctcccgttccctttgtcctctcctctctcttctgcacat ccaaatccaacttccctaccgccattttccgcacttcgataactcgttaacccctcagtctctaatttcttcctc accccaaaaaaaaaaaaactttcatttctctgtcttctttccaaacttttttcttcctcccctgcttacacacaa gaatctgtgatggatgccgcaaatttagtcatgaaatcttccttgttttcgaaatccccatgtcccctttttagt tctaaactcattcctagagcaccaccctctgtctttactctgccttctacctttagacccctcgttaaatgcata caagcttcattcccaccaaaccctgattccaaaaaaccctcaaacaattcaacctttacgtgttcagctgtgact tccttcccttctcaacaatctcagcctcacgcgccttccgatgccaagctccaactcctgatctctgaattccag tccctcgtcgaaccaatggaccgcgtgaaacgcctcttgcactactccacactcctccctccaatggacgcgtcc ttcaaaacccctgagaatcgcgtaccgggttacactacacaggtatggctgaacgtgagtttcgatgaggctgag aacaggatgaaatttttggcggacagtgactcggaaataactaaagggttttgcgcgtgtttggtttcgctgctg gacggggctactcccgatgaggtgctggcgttgaaaacggaggacttgaatgctttgaatgttgcggggttgaac gggaaaggatcggcatctagggcgaatacgtggcataatgtgttggtcagcatgcagaaaaggacaagggcctta gttgcggagcgtgaaggcaggccgcgcggcgagctctttccatctctagtaatcacagctgatggtatccaaccc caaggcagctacgctgaagcccaggcaaggttcctgtttcctgatgaatcaagggtccaaaaacttgccaatttg ctaaaggagaagaaaataggagttgttgctcatttctacatggaccctgaggtgcaaggtgttctaactgcagcg cagaagctttggccccatatacatatatctgattctttagtcatggctgataaagctgtcagtatggcaaaagct ggatgtgaatatatatctgtattgggtgtagatttcatgtcagagaatgtgcgagccattcttgatctagctgga ttcccagaggttggagtttatcggatgtcggacgaacgcattggttgttctttggctgatgctgcagccagccca gcatacttggattatcttaaaacagcttcaacttcttctccatctctgcatgttgtgtacataaatacttcactg gagacaaaagcatattctcatgagcttgttccgactataacatgtacttcctctaatgttgtgcaaactattctg caggcatttgctgaagtacctgacttggaagtgttgtatggtcctgatacctacatgggttcaaacattgcggaa ttgttcacccagatgtccacgatgactgatgaagaaatttctgcgatacatcctttgcacaacagaatctccatt aaatctttgcttcctcgactgcattattttcaggatgggacatgtattgttcatcacctctttggtcatgaagtt gtggagaagataaatgaaatgtatggggatgcattccttactgcacactttgaagttcctggtgaaatgttttcc ctggcaatggaagcgaagaaaaggggcatgggagtagtaggttctacctcgaacatactcgactttatcaaagaa agggtagaagagtccttgaatagaaacgtagatgaacatcttcagtttgttttgggaacggaatcaggaatgatt acggcaatagttgcagcagtcggtaaattactaggttctgctgactcctcttccggtggagcaaaagtaagtgtt gagattgtctttcctgtctcgtcagaatcagtgacaagaacatctacgggttcgcctctggaccaaaataaggtc aatattatacctggagttgcaagtggagaggggtgttctctacatggtggatgtgcctcctgtccatatatgaag atgaactctcttagctcgttgctaaaagtttgccagagcttgccccatggcaaagccgaactttcagcttatgag gcaggacgattcagtttgcgaacccccaagggaaaacaaattgcggatgttggttgtgagccggttctgcacatg agacactttcaggcaacaaagagattaccagagcagctaatcaatcaaatacttcaacctcgtgataatggacga tcaagctctgcttaaacaagacgaaagctagacagacagtggtatttactcgagacaaataaaagtttacttccc ttcaccatacttggcaagggaaggcctagaggagcattatgccagcctcattttttctgcataggacatggatta tacaggaattttatgctgtgcacatgctttggttgttccgtttcttacctttctttttatttttacctggtttaa gtgtgattgtaatagatggaggaaaataatggttgtacttttgtttcccctacaaaatattgaaggtgtttgtat tcgttatgcttaaataagctttaaagctcttttagttttgttcttttttagtgtttggcaatattgtcaaattta ttttggttgaccaatcattttatatttgtatcccttttaacttttcgtaatcccaacattaccct SEQ ID NO: 5 – polypeptide sequence of NtQS-T C133Y; polypeptide mutation is indicated MDAANLVMKSSLFSKSPCPLFSSKLIPRAPPSVFTLPSTFRPLVKCIQASFPPNPDSKKPSNNSTFTCSAVTSFP SQQSQPHAPSDAKLQLLISEFQSLVEPMDRVKRLLHYSTLLPPMDASFKTPENRVPGYTTQVWLNVSFDEAENRM KFLADSDSEITKGFCACLVSLLDGATPDEVLALKTEDLNALNVAGLNGKGSASRANTWHNVLVSMQKRTRALVAE REGRPRGELFPSLVITADGIQPQGSYAEAQARFLFPDESRVQKLANLLKEKKIGVVAHFYMDPEVQGVLTAAQKL WPHIHISDSLVMADKAVSMAKAGCEYISVLGVDFMSENVRAILDLAGFPEVGVYRMSDERIGCSLADAAASPAYL DYLKTASTSSPSLHVVYINTSLETKAYSHELVPTITCTSSNVVQTILQAFAEVPDLEVLYGPDTYMGSNIAELFT QMSTMTDEEISAIHPLHNRISIKSLLPRLHYFQDGTCIVHHLFGHEVVEKINEMYGDAFLTAHFEVPGEMFSLAM EAKKRGMGVVGSTSNILDFIKERVEESLNRNVDEHLQFVLGTESGMITAIVAAVGKLLGSADSSSGGAKVSVEIV FPVSSESVTRTSTGSPLDQNKVNIIPGVASGEGCSLHGGCASCPYMKMNSLSSLLKVCQSLPHGKAELSAYEAGR FSLRTPKGKQIADVGCEPVLHMRHFQATKRLPEQLINQILQPRDNGRSSSA* SEQ ID NO: 6 – part of the wild type polynucleotide sequence of NtQS-T (Ntab- TN90_AYMY-SS91625) gtaccgggttgcactacacag SEQ ID NO: 7 – SEQ ID NO: 6 containing a ‘g’ to ‘a’ mutation shown in bold gtaccgggttacactacacag

[0003] TABLE 1 Alkaloid and nitrate values for the mutant and wild type plants grown under hydroponic conditions in a greenhouse.

[0004] TABLE 2 Alkaloid, nitrate and Tobacco-Specific Nitrosamine (TSNA) values for the mutant and wild type plants grown under field conditions. NAB = N'-nitrosoanabasine NNK = 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone NAT = N′-nitrosoanatabine NNN= N-Nitrosonornicotine

Claims

CLAIMS 1. A Nicotiana tabacum plant or part thereof comprising: (a) a mutated polynucleotide sequence encoding a Nicotiana tabacum quinolinate synthase (NtQS-T) polypeptide comprising a contiguous polypeptide sequence of SEQ ID NO: 3 and comprising at least one mutation therein that modulates alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant; (b) a mutated polypeptide sequence encoded by the polynucleotide sequence set forth in (a); or (c) a construct, vector or expression vector comprising the mutated polynucleotide sequence set forth in (a), wherein the cysteine at amino acid position 133 of NtQS-T is substituted in the mutated polypeptide.

2. The Nicotiana tabacum plant or part thereof according to claim 1, wherein the cysteine at amino acid position 133 of NtQS-T is substituted for an aromatic amino acid selected from the group consisting of histidine, phenylalaine, tryptophan, asparagine and tyrosine.

3. The Nicotiana tabacum plant or part thereof according to claim 1, wherein the cysteine at amino acid position 133 of NtQS-T is substituted for tyrosine (C133Y) in the mutated polypeptide.

4. The Nicotiana tabacum plant or part thereof according to claim 3, wherein the mutated polypeptide comprises the contiguous polypeptide sequence of SEQ ID NO: 5; or wherein the mutated polypeptide consists of the contiguous polypeptide sequence of SEQ ID NO:

5.

5. The Nicotiana tabacum plant or part thereof according to any of the preceding claims, wherein the mutated polynucleotide sequence comprises, consists or consists essentially of the polynucleotide sequence set forth in SEQ ID NO: 4.

6. The Nicotiana tabacum plant or part thereof according to any of the preceding claims, wherein the alkaloids are nicotine, nornicotine, anatabine and myosmine, suitably, wherein the alkaloids are nicotine, nornicotine, anatabine, myosmine and anabasine.

7. The Nicotiana tabacum plant or part thereof according to any of the preceding claims, wherein the at least one mutation reduces alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant.

8. Nicotiana tabacum plant material, cured plant material, or homogenized plant material obtained from the Nicotiana tabacum plant or part thereof according to any of claims 1 to 7.

9. A method for preparing a Nicotiana tabacum plant or part thereof having modulated alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant comprising: (a) providing a Nicotiana tabacum plant; (b) introducing into the Nicotiana tabacum plant one or more mutations in a quinolinate synthase (NtQS-T) polypeptide comprising or consisting of a contiguous polypeptide sequence of SEQ ID NO: 3; (c) determining if the one or more mutations modulate alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant; and (d) identifying a Nicotiana tabacum plant or part thereof comprising one or more mutations in NtQS-T that modulate alkaloid levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from a control plant.

10. A method for producing cured Nicotiana tabacum plant material with an altered amount of alkaloid as compared to control plant material, comprising: (a) providing the Nicotiana tabacum plant or part thereof according to any of claims 1 to 7 or the plant material according to claim 8;(b) harvesting the Nicotiana tabacum plant or part thereof or Nicotiana tabacum plant material; and (c) curing the harvested Nicotiana tabacum plant or the harvested Nicotiana tabacum plant material.

11. The method according to claim 10, wherein the plant material is leaf and the curing method is selected from the group consisting of air curing, fire curing, smoke curing, and flue curing.

12. A cured or dried leaf obtained from the Nicotiana tabacum plant or part thereof according to any of claims 1 to 7 or obtained by the method of claim 10 or 11.

13. The cured or dried leaf according to claim 12, wherein the leaves are air-cured or sun-cured or flue-cured or fermented.

14. A tobacco product comprising the Nicotiana tabacum plant or part thereof of any of claims 1 to 7, the plant material according to claim 8 or the cured or dried leaf according to claim 12 or claim 13.

15. The Nicotiana tabacum plant or part thereof according to any of claims 1 to 7, or the Nicotiana tabacum plant material, cured plant material, or homogenized plant material according to claim 8, or the method according to any of claims 9 to 11, or the cured or dried leaf according to claim 12 or claim 13 or the tobacco product according to claim 14, wherein the at least one mutation modulates N'-nitrosoanabasine (NAB), 4-(methylnitrosamino)-1-(3- pyridyl)-1-butanone (NNK), N′-nitrosoanatabine (NAT) and N-Nitrosonornicotine (NNN) levels in cured or dried leaf obtained from the plant as compared to cured or dried leaf obtained from the control plant.