Metabolic Engineering

Abstract

To provide novel systems for synthesizing QA, which contribute to the technical field.SOLUTION: The invention relates generally to materials and methods for biosynthesizing quillaic acid in a host by expressing heterologous nucleotide sequences in the host, where the heterologous nucleotide sequences encode respective polypeptides which in combination have the QA biosynthesis activity. Example polypeptides include: (i) a beta-amyrin synthase; (ii) an enzyme capable of oxidizing beta-amyrin or an oxidized derivative thereof at the C-28 position to a carboxylic acid; (iii) an enzyme capable of oxidizing beta-amyrin or an oxidized derivative thereof at the C-16α position to an alcohol; and (iv) an enzyme capable of oxidizing beta-amyrin or an oxidized derivative thereof at the C-23 position to an aldehyde. Preferred nucleotide sequences are obtained or derived from Q. saponaria.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates generally to genes and polypeptides that have utility in manipulating or modifying chelic acid production or hydrolysis in host cells. The invention further relates to systems, methods and products utilizing the same. [Background technology]

[0002] Plants produce a wide variety of cyclic triterpenes, including sterols and triterpenoids, which are the major products of the mevalonate (MVA) pathway.

[0003] QS-21 is a complex triterpenoid saponin synthesized by the Chilean tree Quillaja saponaria (Fabaceae).

[0004] The core QS-21 triterpene skeleton is quilacic acid ("QA"), and this scaffold is modified with a branched trisaccharide at the C-3 position and a linear tetrasaccharide at the C-28 position. The C-28 linear tetrasaccharide also features a complex arabinosylated acyl chain (Figure 1).

[0005] QS-21 has utility as an immunostimulatory adjuvant, however, biological sources of QS-21 are limited and chemical synthesis is difficult due to its structural complexity and the complexity of QA. Summary of the Invention [Problem to be solved by the invention]

[0006] It can therefore be seen that a novel system for synthesizing QA, which has utility in, among other things, preparing QS-21, represents a contribution to the art. [Means for solving the problem]

[0007] The core aglycone of QS-21 (chiraic acid) is a derivative of the simple triterpene, β-amyrin, which is synthesized by cyclization of the universal linear precursor 2,3-oxidosqualene (OS) by oxidosqualene cyclase (OSC) (Figure 2).

[0008] The β-amyrin scaffold is further oxidized at C-16α, C-23, and C-28 with an alcohol, aldehyde, and carboxylic acid, respectively, to form quinoline acid. A proposed linear biosynthetic pathway for this is shown in Figure 2, although it is understood that these oxidation reactions can occur in different orders via different intermediates (see Figure 11).

[0009] Therefore, QA biosynthesis from OS involves at least four different enzymatic steps. The enzymes involved include: Oxidosqualene cyclase, an enzyme capable of oxidizing β-amyrin or its oxidized derivatives at C-28 to a carboxylic acid, enzymes capable of oxidizing β-amyrin or its oxidized derivatives, such as oleanolic acid, to alcohols at the C-16α position, Enzymes capable of oxidizing β-amyrin or its oxidized derivatives, such as echinocystic acid, to aldehydes at the C-23 position.

[0010] The oxidized derivatives of β-amyrin resulting from sequential oxidation by these enzymes are shown in Figure 11 and summarized in the table below:

[0011] [Table 1]

[0012] By way of example, using the exemplary scheme of FIG. 2, these enzymes may respectively be: β-amyrin synthase, an enzyme capable of oxidizing β-amyrin to oleanolic acid, an enzyme capable of oxidizing oleanol to echinocystic acid, · An enzyme capable of oxidizing echinocystic acid to QA.

[0013] The present inventors have successfully engineered the entire QA biosynthetic pathway in a heterologous organism that is not otherwise a QA producer. Specifically, the inventors demonstrated this by co-infiltration of N. benthamiana with an Agrobacterium tumefaciens strain. This is the first description of heterologous production of quinoline acid achieved by co-expression of biosynthetic genes and represents a significant contribution to the art.

[0014] More specifically, we demonstrated that a minimum of four additional genes were sufficient for QA biosynthesis (bAS and three CYP450 genes), which advantageously increased product levels when combined with an optional HMG-CoA reductase.

[0015] Furthermore, in a further contribution to the art, the present inventors have identified a gene in Quillaja saponaria that encodes a polypeptide that acts in QA biosynthesis.

[0016] The methods and materials described herein can be used, inter alia, to produce recombinant host organisms (e.g., plants or microorganisms) capable of producing QA even if it is not naturally produced by the wild-type host.

[0017] De novo engineering of quillic acid according to the present invention can produce plants or microorganisms containing large amounts of QA, which can then be used for further chemical synthesis of, for example, QS-21

[18] .

[0018] Thus, one aspect of the present invention provides a method for converting a host from a phenotype in which the host is unable to carry out QA biosynthesis from an OS to a phenotype in which the host is able to carry out said QA biosynthesis, comprising the steps of: expressing a heterologous nucleic acid in a host or one or more cells thereof, said step following a previous step of introducing said nucleic acid into the host or any ancestor thereof; Methods are provided wherein the heterologous nucleic acid comprises multiple nucleotide sequences each encoding a polypeptide having a combination of said QA biosynthetic activities.

[0019] Preferably, the nucleic acid is an enzyme: β-amyrin synthase (bAS) for the cyclization of the universal linear precursor 2,3-oxidosqualene (OS) to triterpenes; CYP450s capable of oxidizing β-amyrin or its oxidized derivatives at C-28 to carboxylic acids, CYP450s capable of oxidizing β-amyrin or its oxidized derivatives, such as oleanolic acid, at C-16α to alcohols, CYP450 capable of oxidizing β-amyrin or its oxidized derivatives, such as echinocystic acid, to aldehydes at C-23 The nucleotide sequence encodes some or all (one, two, three or four) of the nucleotide sequences.

[0020] In certain embodiments, these CYP450 enzymes are: CYP450, which can oxidize β-amyrin at C-28 to a carboxylic acid forming oleanolic acid; CYP450 capable of oxidizing oleanolic acid at the C-16α position to an alcohol forming echinocystic acid, CYP450 capable of oxidizing echinocystic acid at C-23 to an aldehyde forming QA may be.

[0021] Other possible intermediates will be recognized by those skilled in the art in light of the disclosure herein and particularly FIG.

[0022] For brevity, these enzymes may be referred to herein as "bAS," "C-28 oxidase," "C-16 alpha oxidase," and "C-23 oxidase," respectively.

[0023] For further brevity, these enzymes may be collectively referred to herein as "QA polypeptides."

[0024] In one embodiment, at least one of the QA polypeptides originates from (is derived from) Q. saponaria. Preferably, two, three or all four of the QA polypeptides originate from Q. saponaria.

[0025] In one embodiment: C-28 oxidase is CYP716

[0026] C-16α is CYP716 or CYP87

[0027] The C-23 oxidase is CYP714, CYP72, or CYP94

[0028] Preferred genes or polypeptides for use in practicing the present invention are shown in the Sequence Appendix.

[0029] In preferred embodiments, one, two, three or four of the respective polypeptides are selected from the Q. saponaria sequences set forth in Table 1, for example as follows: β-amyrin synthase (bAS) = SEQ ID NO: 2 C-28 oxidase = SEQ ID NO: 4 C-16 alpha oxidase = SEQ ID NO: 6 C-23 oxidase = SEQ ID NO: 8 or a variant or fragment thereof as described below.

[0030] In other embodiments, one, two, or three of the respective polypeptides are selected from the non-Q. saponaria sequences set forth in Tables 2a, 2b, or 2c, for example, as follows: C-28 oxidase = SEQ ID NO: 18 C-16 alpha oxidase = SEQ ID NO: 10 or 12 C-23 oxidase = SEQ ID NO: 14 or 16 or a variant or fragment thereof as described below.

[0031] In certain embodiments, the QA polypeptide is encoded by a nucleotide sequence set forth in any of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, or 17, or a variant or fragment thereof as described below.

[0032] In other embodiments, the C-28 oxidase is a polypeptide encoded by one of the non-Q. saponaria accessions set forth in Table 2d as SEQ ID NOs: 19-28: (VvCYP716A15, VvCYP716A17, PgCYP716A52v2, MlCYP716A75, CqCYP716A78, CqCYP716A79, BvCYP716A80, BvCYP716A81, MdCYP716A175, or CrCYP716AL1), or a variant or fragment thereof as described below. These nucleotide sequences are referred to herein as SEQ ID NOs: 19-28, respectively.

[0033] For brevity, the nucleotide sequences of either of Tables 1 and 2 may be referred to herein as the "QA gene."

[0034] variant In addition to the use of these QA genes (and polypeptides), the present invention encompasses the use of variants of these genes (and polypeptides).

[0035] A "variant" QA nucleic acid or QA polypeptide molecule shares homology with or is identical to all or a portion of a QA gene or polypeptide described herein.

[0036] Variant polypeptides share the relevant biological activity of the native QA polypeptide. Variant nucleic acids encode the relevant variant polypeptides.

[0037] In this context, the "biological activity" of a QA polypeptide is its ability to catalyze the respective reaction shown in Figure 2 and described above (i.e., cyclase or oxidase activity). The relevant biological activities can be assayed in vitro based on the reaction shown in Figure 2 (or the corresponding oxidation reaction, e.g., as in Figure 11). Alternatively, they can be assayed by in vivo activity as described in the Examples, i.e., by introducing multiple heterologous constructs to produce QA, which can be assayed by LC-MS, etc.

[0038] Table 8 shows pairwise comparisons of the P450 enzymes described herein obtained using Clustal Omega (version 1.2.4 accessed via https: / / www.ebi.ac.uk).

[0039] Variants of the sequences disclosed herein preferably share at least 50%, 55%, 56%, 57%, 58%, 59%, 60%, 65%, or 70%, or 80% identity, and most preferably at least about 90%, 95%, 96%, 97%, 98%, or 99% identity. Such variants are sometimes referred to herein as "substantially homologous."

[0040] Preferred variants may be: (i) Naturally occurring nucleic acids, such as alleles (containing polymorphisms or mutations in one or more bases) or pseudoalleles (which may occur at loci closely related to the QA genes of the present invention). Also included are paralogs, isogenes, or other homologous genes belonging to the same family as the QA genes of the present invention. Also included are orthologs or homologs from other plant species.

[0041] Table 4 shows the minor sequence differences identified between the gene sequences found in the 1KP dataset and the sequenced clones obtained by PCR from Q. saponaria plants in the present disclosure. This demonstrates that even in the approximately 1500 bp OQHZ-2012090, 19 mutations (more than 1% mutations) were identified. Specifically, the use of QA genes or polypeptides containing one or more of the mutations listed in Table 4 in their respective sequences is contemplated by the present disclosure. Furthermore, nucleic acid molecules encoding amino acid sequences that are homologs of the QA genes of the present invention are included within the scope of the present invention. Homology can be at the nucleotide sequence and / or amino acid sequence level, as explained below.

[0042] (ii) Artificial nucleic acids, which can be prepared by one skilled in the art in light of the present disclosure. Such derivatives can be prepared, for example, by site-directed or random mutagenesis, or by direct synthesis. Preferably, the variant nucleic acids are generated either directly or indirectly (e.g., via one or more amplification or replication steps) from an original nucleic acid having all or part of the sequence of a QA gene of the present invention.

[0043] Also included are nucleic acids which correspond to the above nucleic acids but which are extended at the 3' or 5' ends.

[0044] As used herein, the term "QA variant nucleic acid" encompasses all of these possibilities. When used in the context of a polypeptide or protein, it refers to the encoded expression product of a variant nucleic acid.

[0045] In each case, preferred QA biosynthetic modified nucleic acids are any of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15 and 17, or substantially homologous variants thereof.

[0046] Preferred QA biosynthetic modified polypeptides are any of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16 and 18, or substantially homologous variants thereof.

[0047] Other preferred QA biosynthetic modified nucleic acids for use in the present invention are any of SEQ ID NOs: 19-28, or substantially homologous variants or fragments thereof. Other preferred QA biosynthetic modified polypeptides are polypeptides encoded by any of these sequences or variants or fragments.

[0048] Complementary genes In embodiments of the invention, in addition to the QA genes and variant nucleic acids of the invention described herein, it may be preferable to introduce additional genes that can affect the flux of QA production.

[0049] For example, MVA is a key intermediate in triterpenoid synthesis, and therefore, expression of the rate-limiting MVA pathway genes in the host may be desirable to maximize the yield of QA.

[0050] HMG-CoA reductase (HMGR) is thought to be the rate-limiting enzyme in the MVA pathway.

[0051] The use of a recombinant feedback-insensitive truncated form of HMGR (tHMGR) has been demonstrated to increase triterpene (β-amyrin) content upon transient expression in Nicotiana benthamiana [5], also Figure 10.

[0052] Thus, one embodiment of the present invention includes the use of a heterologous HMGR (e.g., a feedback-insensitive HMGR) in conjunction with the QA genes described herein. Exemplary HMGR coding or polypeptide sequences include SEQ ID NOs: 29-32, or variants or fragments thereof. Variants may be homologs, alleles, or artificial derivatives, etc., as described above in connection with the QA genes or polypeptides. For example, an HMGR native to the host utilized, such as a yeast HMGR in a yeast host, may be preferred. HMGR genes are known in the art and can be appropriately selected in light of the present disclosure.

[0053] It has also been reported that squalene synthase (SQS; see Figure 10) is a potential rate-limiting step [5].

[0054] Thus, one embodiment of the present invention includes the use of a heterologous SQS in conjunction with the QA genes described herein and optionally HMGR.

[0055] Examples of SQS code or polypeptide sequences include SEQ ID NOs: 33-34, or variants or fragments thereof. Variants may be homologs, alleles, or artificial derivatives, as described above in connection with the QA genes or polypeptides. For example, an SQS native to the host being used, such as yeast SQS in a yeast host, may be preferred. SQS genes are known in the art and can be appropriately selected in light of the present disclosure, as needed.

[0056] When using certain hosts (e.g., yeast), it may be desirable to introduce additional genes to improve the flux of QA production. Examples can include one or more plant cytochrome P450 reductases (CPRs) that serve as redox partners for the introduced P450. Thus, one embodiment of the present invention includes the use of a heterologous cytochrome P450 reductase, such as AtATR2 (Arabidopsis thaliana cytochrome P450 reductase 2), in conjunction with the QA genes described herein. Examples of AtATR2 coding or polypeptide sequences include SEQ ID NOs: 35-36, or variants or fragments thereof. Variants can be homologs, alleles, or artificial derivatives, etc., as described in connection with the QA genes or polypeptides described above.

[0057] It will be understood by those of skill in the art in light of the present disclosure that additional genes may be utilized in the practice of the present invention to provide further activity and / or improve expression or activity. These include those that express cofactors or helper proteins, or other factors. Examples may include genes involved in the synthesis of QS-21 from QA.

[0058] For brevity, any of these nucleic acid sequences ("QA genes of the invention" and "QA variant nucleic acids," as well as other genes that result in QA synthesis or secondary modifications to QA) may be referred to herein as "QA nucleic acids" or "QA biosynthetically modified nucleic acids." Similarly, the encoded polypeptides may be referred to herein as "QA polypeptides" or "QA biosynthetically modified polypeptides."

[0059] It is understood that when these generic terms are used in relation to any aspect or embodiment, the meaning is to be construed as applying to any of these sequences individually.

[0060] vector In one aspect of the present invention, a method is disclosed that utilizes the co-infiltration of multiple Agrobacterium tumefaciens strains, each harboring one or more of the QA nucleic acids described above for their coordinated expression in the biosynthetic pathways described above.

[0061] In some embodiments, for example, at least three or four different Agrobacterium tumefaciens strains each carrying a QA nucleic acid are co-infiltrated.

[0062] These genes can be displayed from transient expression vectors.

[0063] A preferred expression system utilizes what is referred to as the "Hyper-Translatable" Cowpea Mosaic Virus ("CPMV-HT") system, described in WO2009 / 087391, the disclosure of which is specifically incorporated herein in support of embodiments using vectors based on the CPMV-HT system, e.g., the pEAQ-HT expression plasmid.

[0064] Thus, vectors (typically binary vectors) for use in the present invention typically contain: (i) a promoter, operably linked to: (ii) an enhancer sequence derived from the RNA-2 genome segment of a bipartite RNA virus, in which the target initiation site in the RNA-2 genome segment has been mutated; (iii) the QA nucleic acid sequence described above; (iv) a transcription termination sequence, and optionally (v) a 3'UTR located upstream of the transcription termination sequence; The expression cassette comprises:

[0065] Further examples of vectors and expression systems useful in practicing the present invention are described in more detail herein below.

[0066] host In embodiments of the present invention, a host can be converted from a phenotype in which the host is unable to carry out efficient QA biosynthesis from OS to a phenotype in which the host is able to carry out said QA biosynthesis, such that QA can be recovered from the host or utilized in vivo to synthesize downstream products. Examples of hosts include plants such as Nicotiana benthamiana and microorganisms such as yeast. These are described in more detail below.

[0067] The invention can include transforming a host with a heterologous nucleic acid as described above by introducing a QA nucleic acid into a host cell via a vector and causing or allowing recombination between the vector and the host cell genome to introduce a nucleic acid according to the invention into the genome.

[0068] Another aspect of the invention provides a host cell transformed with heterologous nucleic acid, wherein the heterologous nucleic acid comprises a plurality of nucleotide sequences encoding polypeptides each having a combination of the QA biosynthetic activities described above, A host cell is provided in which expression of the nucleic acid confers to the transformed host the ability to carry out QA biosynthesis from OS or improves said ability in the host.

[0069] The present invention further encompasses host cells, particularly plant or microbial cells, transformed with the above-described nucleic acids or vectors (e.g., containing QA biosynthetic modified nucleotide sequences). In transgenic host cells (i.e., transgenic for the nucleic acid of interest), the transgene may be on an extragenomic vector or may be stably integrated into the genome, preferably. More than one heterologous nucleotide sequence may be present per haploid genome.

[0070] The methods and materials described herein can be used, inter alia, to generate stable crop plants that accumulate QAs.

[0071] Also provided is a plant comprising a plant cell according to the invention.

[0072] Production of products The methods described above can be used to produce QAs in heterologous hosts. QAs generally do not naturally occur in the species into which they are introduced.

[0073] QA from the plants or methods of the present invention may be isolated and commercially utilized.

[0074] The above method can form part of, or in some cases form a step in, a method for producing QS-21 in a host. The method can include culturing the host (if it is a microorganism) or growing the host (if it is a plant) and then harvesting and purifying the QA or QS-21 product therefrom. The product so produced forms a further aspect of the invention. The utility of the QA or QS-21 product has been described above.

[0075] Alternatively, QA may be recovered to allow further chemical synthesis of QS-21

[18] .

[0076] The novel gene of the present invention In support of the present invention, the inventors have newly characterized sequences from Q. saponaria (see SEQ ID NOs: 1-8) that are thought to be involved in the synthesis of QA in that species.

[0077] In preferred embodiments, the methods of the invention involve the use of one or more of these newly characterized QA nucleic acids of the invention (e.g., one, two, three, or four such QA nucleic acids), optionally in combination with the manipulation of other genes affecting QA biosynthesis known in the art.

[0078] These newly characterized QA sequences from Q. saponaria (SEQ ID NOs: 1-8) as well as variants derived from these sequences and sources of these sequences, and methods of using them, themselves form aspects of the present invention.

[0079] Some aspects and embodiments of the invention will now be described in more detail. DETAILED DESCRIPTION OF THE INVENTION

[0080] In various embodiments, the present invention provides a means to manipulate the total level of QA in a host cell, such as a microorganism or a plant.

[0081] In one aspect of the invention, the QA biosynthetic modified nucleic acids described above are in the form of recombinant, preferably replicable, vectors.

[0082] A "vector" is defined to include, inter alia, any plasmid, cosmid, phage, or Agrobacterium binary vector, in double- or single-stranded, linear, or circular form, which may or may not be self-transmissible or mobilizable and which is capable of transforming a prokaryotic or eukaryotic host either by integration into the cellular genome or by extrachromosomal presence (e.g., a self-replicating plasmid with an origin of replication).

[0083] As is well known to those skilled in the art, a "binary vector" system contains (a) border sequences that allow the transfer of the desired nucleotide sequence into the plant cell genome; and (b) the desired nucleotide sequence itself, which generally includes an expression cassette for (i) a plant-active promoter operably linked to (ii) a targeting sequence and / or enhancer, as needed. The desired nucleotide sequence is located between the border sequences and can be inserted into the plant genome under appropriate conditions. Binary vector systems generally require other sequences (derived from A. tumefaciens) to effect integration. This can generally be achieved through the use of Agrobacterium-mediated transient transformation, a process known as "agroinfiltration." Briefly, this technique is based on the ability of Agrobacterium tumefaciens to transfer a portion of its DNA ("T-DNA") into host cells, where it can be integrated into the nuclear DNA. The T-DNA is defined by left and right border sequences, approximately 21-23 nucleotides in length. Infiltration can be achieved, for example, by injection (in the leaves) or vacuum (whole plant). In the present invention, border sequences are generally included near the desired nucleotide sequence (T-DNA) introduced by one or more vectors into the plant material by agroinfiltration.

[0084] In general, those skilled in the art are fully capable of constructing vectors and designing protocols for recombinant gene expression. Suitable vectors containing appropriate regulatory sequences, including promoter sequences, transcription termination fragments, polyadenylation sequences, enhancer sequences, marker genes, and other sequences as needed, can be selected or constructed. For further details, see, for example, Molecular Cloning: a Laboratory Manual: 2nd ed., Sambrook et al., 1989, Cold Spring Harbor Laboratory Press, or Current Protocols in Molecular Biology, 2nd ed., Ausubel et al., eds., John Wiley & Sons, 1992.

[0085] Specifically included are shuttle vectors, which refer to DNA vehicles that are naturally or by design capable of replication in two different host organisms, which may be selected from actinomycetes and related species, bacteria and eukaryotes (e.g., higher plant, moss, yeast or fungal cells).

[0086] Vectors containing nucleic acids according to the invention need not contain promoters or other regulatory sequences, particularly if the vector is used to introduce the nucleic acid into a cell for recombination into the genome.

[0087] Preferably, the nucleic acid in the vector is under the control of, and operably linked to, a suitable promoter or other regulatory element for transcription in a host cell, such as a microorganism, e.g., yeast and bacteria, or a plant cell. The vector may also be a bifunctional expression vector that functions in multiple hosts. In the case of genomic DNA, it may contain its own promoter or other regulatory element (optionally in combination with a heterologous enhancer, such as the 35S enhancer described in the Examples below). The advantage of using a native promoter is that it can avoid pleiotropic responses. In the case of cDNA, it may be under the control of a suitable promoter or other regulatory element for expression in a host cell.

[0088] By "promoter" is meant a sequence of nucleotides from which transcription of DNA operably linked downstream (ie, in the 3' direction on the sense strand of double-stranded DNA) can be initiated.

[0089] "Operably linked" means association as part of the same nucleic acid molecule, appropriately positioned and oriented for transcription to be initiated from the promoter. DNA operably linked to a promoter is "under the transcription initiation control" of the promoter.

[0090] In a preferred embodiment, the promoter is an inducible promoter.

[0091] The term "inducible" as applied to a promoter is well understood by those of skill in the art. Essentially, expression under the control of an inducible promoter is "switched on" or increased in response to a given stimulus. The nature of the stimulus varies among promoters. Some inducible promoters cause little or undetectable levels of expression (or no expression) in the absence of the appropriate stimulus. Other inducible promoters cause detectable constitutive expression in the absence of the stimulus. Regardless of the level of expression in the absence of the stimulus, expression from any inducible promoter increases in the presence of the correct stimulus.

[0092] Thus, the nucleic acids of the present invention can be placed under the control of an externally inducible gene promoter to place expression under the user's control. An advantage of introducing heterologous genes into plant cells, particularly when the cells are contained in a plant, is the ability to place gene expression under the control of a promoter of choice, so that gene expression, and thereby QA biosynthesis, can be influenced according to choice. Furthermore, mutants and derivatives of wild-type genes, e.g., with higher or lower activity than the wild-type, can be used in place of endogenous genes.

[0093] Thus, this aspect of the invention provides a genetic construct, preferably a replicable vector, comprising a promoter (optionally inducible) operably linked to a nucleotide sequence provided by the invention, e.g., a QA biosynthetic modified gene, most preferably one of the Qs QA nucleic acids described below, or a derivative thereof.

[0094] Of particular interest in the context of the present invention are nucleic acid constructs that function as plant vectors. Specific procedures and vectors that have previously been used with widespread success in plants are described by Guerineau and Mullineaux (1993) (Plant transformation and expression vectors. In: Plant Molecular Biology Labfax (Croy RRD ed) Oxford, BIOS Scientific Publishers, pp 121-148). Suitable vectors may include plant virus-derived vectors (see, e.g., EP-A-194809).

[0095] Preferably, the vectors of the invention for use in plants contain border sequences that allow the transfer and integration of the expression cassette into the plant genome. Preferably, the construct is a plant binary vector. Preferably, the binary transformation vector is based on pPZP (Hajdukiewicz, et al. 1994). Other exemplary constructs include pBin19 (see Frisch, DA, LW Harris-Haller, et al. (1995). "Complete Sequence of the binary vector Bin 19." Plant Molecular Biology 27: 405-409).

[0096] Suitable promoters that operate in plants include the cauliflower mosaic virus 35S (CaMV 35S). Other examples are disclosed in Lindsey & Jones (1989) "Plant Biotechnology in Agriculture," Published by OU Press, Milton Keynes, UK, p. 120. Promoters can be selected to contain one or more sequence motifs or elements that confer developmental and / or tissue-specific regulatory control of expression. Inducible plant promoters include the ethanol-inducible promoter of Caddick et al. (1998) Nature Biotechnology 16:177-180.

[0097] If desired, a selectable genetic marker can be included in the construct, such as one that confers a selectable phenotype, such as resistance to antibiotics or herbicides (e.g., kanamycin, hygromycin, phosphinotricin, chlorsulfuron, methotrexate, gentamicin, spectinomycin, imidazolinones, and glyphosate). Positive selection systems such as those described in Haldrup et al., 1998, Plant Molecular Biology 37, 287-296 can be used to generate antibiotic-independent constructs.

[0098] As explained above, a preferred vector is the "CPMV-HT" vector as described in WO2009 / 087391. The following examples demonstrate the use of these pEAQ-HT expression plasmids.

[0099] These vectors (typically binary vectors) for use in the present invention typically comprise: (i) a promoter, operably linked to: (ii) an enhancer sequence derived from the RNA-2 genome segment of a bipartite RNA virus, in which the target initiation site in the RNA-2 genome segment has been mutated; (iii) the QA nucleic acid sequence described above; (iv) a transcription termination sequence, and optionally (v) a 3'UTR located upstream of the transcription termination sequence; The expression cassette comprises:

[0100] As referred to herein, an "enhancer" sequence (or enhancer element) is a sequence derived from (or sharing homology with) the RNA-2 genome segment of a bipartite RNA virus, such as a comovirus, in which the target initiation site has been mutated. Such sequences can enhance downstream expression of heterologous ORFs to which they are linked. Without limitation, it is believed that such sequences, when present in a transcribed RNA, can enhance translation of heterologous ORFs to which they are linked.

[0101] The "target initiation site" referred to herein is the initiation site (start codon) in the wild-type RNA-2 genome segment of a bipartite virus (e.g., a comovirus) from which the enhancer sequence in question is derived and which serves as the initiation site for the production (translation) of the longer of the two carboxy-coterminal proteins encoded by the wild-type RNA-2 genome segment.

[0102] Typically, the RNA virus is a comovirus as previously described herein.

[0103] The most preferred vector is the pEAQ vector of WO2009 / 087391, which allows for a direct cloning version by using a polylinker between the 5' leader and 3' UTR of an expression cassette containing the translational enhancer of the present invention located in a T-DNA that also contains a suppressor of gene silencing and an NPTII cassette.

[0104] The presence of a gene silencing suppressor in such a gene expression system is preferred, but not essential.Gene silencing suppressors are known in the art and are described in WO / 2007 / 135480.They include HcPro from potato virus Y, He-Pro from TEV, P19 from TBSV, rgsCam, B2 protein from FHV, CPMV small coat protein, and coat protein from TCV.When producing stable transgenic plants, a preferred suppressor is the P19 suppressor incorporating the R43W mutation.

[0105] The present invention also provides methods comprising introducing such constructs into plant cells or microbial (e.g., bacterial, yeast or fungal) cells and / or inducing expression of the constructs in plant cells by application of an appropriate stimulus, e.g., an effective exogenous inducer.

[0106] As an alternative to microorganisms, cell suspension cultures of QA-producing plant species, including the moss Physcomitrella patens, can be grown in fermentation tanks (see, e.g., Grotewold et al. (Engineering Secondary Metabolites in Maize Cells by Ectopic Expression of Transcription Factors, Plant Cell, 10, 721-740, 1998)).

[0107] In a further aspect of the present invention, a host cell, in particular a plant or microbial cell, containing a heterologous construct according to the present invention is disclosed.

[0108] The host cell descriptions above regarding the reconstitution of QA biosynthesis in heterologous organisms apply mutatis mutandis here.

[0109] Thus, a further aspect of the present invention provides a method of transforming a plant cell which involves the introduction of a construct as described above into the plant cell, causing or allowing recombination between the vector and the plant cell genome to introduce a nucleic acid according to the present invention into the genome.

[0110] The present invention further encompasses host cells, particularly plant or microbial cells, transformed with a nucleic acid or vector (e.g., comprising a QA biosynthetic modified nucleotide sequence) according to the present invention. In transgenic plant cells (i.e., transgenic for the nucleic acid in question), the transgene may be on an extragenomic vector or may be preferably stably integrated into the genome. More than one heterologous nucleotide sequence may be present per haploid genome.

[0111] Yeasts have been widely used as hosts for triterpene production [6–8, 19–22] and may therefore be well suited for QA biosynthesis.

[0112] Thus, in one embodiment, the host is yeast. For such hosts, it may be desirable to introduce additional genes to improve the flux of QA production as described above. Examples may include one or more plant cytochrome P450 reductases (CPRs) [6], which serve as redox partners for the introduced P450, as well as HMGR.

[0113] Plants containing plant cells transformed as described above form a further aspect of the present invention.

[0114] If desired, after transformation of the plant cells, plants can be regenerated, for example, from single cells, callus tissue, or leaf discs, as is standard in the art. Nearly any plant can be regenerated entirely from plant cells, tissues, and organs. Available techniques are reviewed in Vasil et al., Cell Culture and Somatic Cell Genetics of Plants, Vol. I, II, and III, Laboratory Procedures and Their Applications, Academic Press, 1984, and Weissbach and Weissbach, Methods for Plant Molecular Biology, Academic Press, 1989.

[0115] In addition to regenerated plants, the present invention encompasses all of the following: clones of such plants, seeds, autologous or hybrid progeny and descendants (e.g., F1 and F2 descendants). The present invention also provides plant propagules from such plants, i.e., any part that can be used for reproduction or propagation, sexual or asexual, including cuttings, seeds, etc. The present invention also provides any part of these plants, which in all cases contain the plant cells or heterologous QA biosynthetic modified DNA described above.

[0116] The present invention also encompasses expression products of any of the disclosed encoding QA biosynthetic modified nucleic acid sequences and methods for producing the expression products by expression from the encoding nucleic acid, and therefore under suitable conditions, which may be in a suitable host cell.

[0117] As described below, a plant background such as that described above may be native or transgenic for one or more other genes, for example, related to QA biosynthesis or otherwise affecting its phenotype or trait.

[0118] In modifying the host phenotype, the QA nucleic acids described herein may be used in combination with any other gene, such as a transgene, that affects the rate or yield of QA, or modifications thereof, or any other phenotypic trait or desired characteristic.

[0119] Through the use of genetic combinations, plants or microorganisms (eg, bacteria, yeast, or fungi) can be tailored to enhance production of desired precursors or reduce undesirable metabolism.

[0120] Alternatively, downregulation of genes in the host may be desirable, for example, to reduce undesired metabolism or fluxes that may affect QA yield.

[0121] Such downregulation can be achieved by methods known in the art, for example, by using antisense technology.

[0122] When antisense gene or partial gene sequence is used to down-regulate gene expression, nucleotide sequence is placed in "reverse" direction under the control of promoter, so that transcription produces RNA complementary to normal mRNA transcribed from the "sense" strand of target gene.See, for example, Rothstein et al., 1987; Smith et al. (1988) Nature 334, 724-726; Zhang et al. (1992) The Plant Cell 4, 1575-1588; English et al. (1996) The Plant Cell 8, 179-188.Antisense technology is also reviewed in Bourque (1995), Plant Science 105, 125-149, and Flavell (1994) PNAS USA 91, 3490-3496.

[0123] An alternative to antisense is to use sense, i.e., a copy of all or part of the target gene inserted in the same direction as the target gene, to achieve co-suppression to reduce the expression of the target gene.See, for example, van der Krol et al. (1990) The Plant Cell 2, 291-299; Napoli et al. (1990) The Plant Cell 2, 279-289; Zhang et al. (1992) The Plant Cell 4, 1575-1588, and US-A-5,231,020.Further improvements in gene silencing or co-suppression technology can be found in WO95 / 34668 (Biosource); Angell & Baulcombe (1997) The EMBO Journal 16, 12:3675-3684; and Voinnet & Baulcombe (1997) Nature 389:553.

[0124] Double-stranded RNA (dsRNA) has been found to be more effective in gene silencing than either only sense strand or only antisense strand (Fire A. et al. Nature, Vol 391, (1998)). dsRNA-mediated silencing is gene-specific and is often referred to as RNA interference (RNAi) (see also Fire (1999) Trends Genet. 15: 358-363, Sharp (2001) Genes Dev. 15: 485-490, Hammond et al. (2001) Nature Rev. Genes 2: 1110-1119 and Tuschl (2001) Chem. Biochem. 2: 239-245).

[0125] RNA interference is a two-step process. First, dsRNA is cleaved intracellularly to generate small interfering RNAs (siRNAs) of approximately 21-23 nt in length with a 5'-terminal phosphate and a short 3' overhang (approximately 2 nt). The siRNAs target the corresponding mRNA sequence for specific destruction (Zamore PD Nature Structural Biology, 8, 9, 746-750, (2001)).

[0126] Another methodology known in the art for downregulating target sequences is the use of "microRNAs" (miRNAs), as described, for example, in Schwab et al., 2006, Plant Cell 18, 1121-1133. This technology utilizes artificial miRNAs that can be encoded by stem-loop precursors incorporating appropriate oligonucleotide sequences, which can be generated using well-defined rules in light of the disclosure herein.

[0127] The methods of the present invention encompass both in vitro and in vivo production or manipulation of one or more QAs. For example, QA polypeptides can be utilized for fermentation via expression in microorganisms such as, for example, E. coli, yeast, and filamentous fungi. In one embodiment, one or more newly characterized Qs QA sequences of the present invention can be used in these organisms in combination with one or more other biosynthetic genes.

[0128] In vivo methods are broadly described above and generally involve causing or permitting transcription of a recombinant nucleic acid molecule encoding a QA polypeptide, followed by translation from that recombinant nucleic acid molecule.

[0129] In other aspects of the invention, the QA polypeptides (enzymes) may be used in vitro, for example in isolated, purified or semi-purified form. Optionally, they may be the expression product of a recombinant nucleic acid molecule.

[0130] As explained above, QS-21 is a purified plant extract that enhances the immune system's ability to respond to vaccine antigens.

[0131] QS-21 has utility as an immunological adjuvant, believed to enhance both humoral and cell-mediated immunity. QS-21 is under clinical evaluation as an additive to various investigational vaccines, including those against HIV, malaria, and cancer. It is a component of the FDA-approved Shingrix shingles vaccine.

[0132] Newly characterized sequences from Quillaja saponaria As noted above, in support of the present invention, the present inventors have identified genes from Q. saponaria that are believed to encode polypeptides that act in QA biosynthesis (see SEQ ID NOS: 1-8 in Table 1).

[0133] In certain embodiments of the invention, the QA nucleic acids are derived from Q. saponaria (SEQ ID NOS: 1-8). Although the key steps described herein for QA production (triterpene synthesis and oxidation) are believed to likely occur on the cytoplasmic surface of the endoplasmic reticulum, such genes may be preferred for use in preparing particularly stable transgenic plant hosts, as these native plant genes may be most efficiently processed and function in the appropriate compartments of these hosts.

[0134] The above newly characterized QA biosynthetic genes from Q. saponaria. As such, they form aspects of the present invention.

[0135] In a further aspect of the present invention, it is disclosed that nucleic acids that are variants of the QA nucleic acids are derived from Q. saponaria as described above.

[0136] Similar to the native QA genes described herein, such variants can be used to alter the QA content of plants, as assessed by the methods disclosed herein. For example, variant nucleic acids can include sequences encoding variant QA polypeptides that share the relevant biological activity of the native QA polypeptides, as described above. Examples include variants of any of SEQ ID NOs: 2, 4, 6, or 8.

[0137] derivative Described herein are methods for producing derivative nucleic acids that involve modifying any of the QA genes of the invention disclosed above, particularly the QA sequence from Q. saponaria.

[0138] Alterations may be desirable for a number of reasons. For example, alterations may introduce or remove restriction endonuclease sites or change codon usage. This may be particularly desirable when the Qs gene is expressed in an alternative host, e.g., a microbial host such as yeast. Methods for codon-optimizing genes for this purpose are known in the art (see, e.g., Elena, Claudia, et al. "Expression of codon optimized genes in microbial systems: current industrial applications and perspectives." Frontiers in microbiology 5 (2014)). Thus, the sequences described herein that include codon modifications to maximize yeast expression represent specific embodiments of the invention.

[0139] Alternatively, changes to the sequence can be by one or more (e.g., several) additions, insertions, deletions, or substitutions of one or more nucleotides in the nucleic acid, which lead to the addition, insertion, deletion, or substitution of one or more (e.g., several) amino acids in the encoded polypeptide, to produce a derivative.

[0140] Such alterations can modify sites required for post-translational modification, such as cleavage sites in the encoded polypeptide; motifs in the encoded polypeptide for phosphorylation, etc. If it is desired to isolate the expressed protein from a microbial system, a leader or other targeting sequence (e.g., membrane or Golgi location sequence) may be added to the expressed protein to determine its location after expression.

[0141] Other desirable mutations can be random or site-directed mutagenesis to alter the activity (e.g., specificity) or stability of the encoded polypeptide. The alteration can be conservative, i.e., substituting one hydrophobic residue, such as isoleucine, valine, leucine, or methionine, for another, or substituting one polar residue for another, e.g., arginine for lysine, glutamic acid for aspartic acid, or glutamine for asparagine. As is well known to those skilled in the art, altering the primary structure of a polypeptide by conservative substitutions does not significantly alter the activity of the peptide, because the side chain of the amino acid inserted into the sequence can form similar bonds and contacts as the side chain of the amino acid that has been substituted out. This is true even when the substitution is in a region important in determining peptide conformation. Variants with non-conservative substitutions are also included. As is well known to those skilled in the art, substitutions in regions of a peptide that are not important in determining peptide conformation do not significantly affect its activity, because they do not significantly alter the three-dimensional structure of the peptide. In regions that are important in determining peptide conformation or activity, such changes can confer advantageous properties to the polypeptide. Indeed, changes such as those described above can confer slightly advantageous properties to the peptide, such as altered stability or specificity.

[0142] piece The present invention can utilize fragments of the polypeptides encoding the QA genes of the present invention disclosed above, in particular the QA sequence from Q. saponaria.

[0143] Thus, the present invention provides for the production and use of fragments of the full-length QA polypeptides of the invention disclosed herein, particularly active portions thereof. An "active portion" of a polypeptide refers to a peptide that is less than the full-length polypeptide but retains its essential biological activity.

[0144] A "fragment" of a polypeptide refers to a stretch of amino acid residues of at least about 5-7 contiguous amino acids, often at least about 7-9 contiguous amino acids, typically at least about 9-13 contiguous amino acids, and most preferably at least about 20-30 or more contiguous amino acids. A polypeptide fragment may contain one or more epitopes useful for raising antibodies against any portion of the amino acid sequences disclosed herein. Preferred epitopes are those to which an antibody can specifically bind, which may be interpreted as binding to a polypeptide of the present invention or a fragment thereof with an affinity that is at least about 1000-fold greater than the affinity of other polypeptides.

[0145] The particular fragment disclosed herein is a shorter isoform of CYP716-2012090, which is shown in SEQ ID NO: 6, i.e., lacking the N-terminal 21 amino acids underlined in the Sequence Appendix.

[0146] For brevity, any of these QA sequences or variants (e.g., derivatives such as fragments thereof) from Q. saponaria may be referred to as "Qs QA sequences (or nucleic acids, or polypeptides)". These Qs QA polypeptides, and the nucleic acids encoding them, form an aspect of the present invention.

[0147] When the term is used generally, it is understood that it also applies individually to any of these sequences.

[0148] Thus, in one aspect of the invention, an isolated nucleic acid encoding any of these polypeptides (2, 4, 6, or 8) is disclosed. Preferably, this may have the sequence of 1, 3, 5, or 7. Other nucleic acids of the invention include degenerate equivalents thereof or homologous variants (e.g., derivatives) thereof.

[0149] Aspects of the present invention further include an isolated nucleic acid comprising a sequence that is complementary to any of the sequences set forth herein below.

[0150] The use of Qs QA sequences to catalyze their respective biological activities (as depicted in Figure 1) forms another aspect of the present invention. For brevity, any of these sequences may be referred to as a "Qs QA sequence."

[0151] Thus, the present invention further provides a method for influencing or affecting QA biosynthesis in a host, such as a plant, comprising the step of causing or enabling transcription in a cell of the plant of a heterologous Qs QA nucleic acid as described above, which step may be preceded by a prior step of introducing a Qs QA nucleic acid into a cell of the plant or an ancestor thereof.

[0152] Such a method will usually form part of, or optionally a step in, a method for producing QA in a host such as a plant, which preferably utilises a QA-modified polypeptide of the invention as described above (e.g., Table 1) or a derivative thereof, or a nucleic acid encoding either.

[0153] In a further embodiment, there are provided antibodies raised against the Qs QA polypeptides or peptides of the invention.

[0154] Some aspects of the invention related to the heterologous reconstitution of the biosynthetic pathways described above will now be described in more detail.

[0155] "Nucleic acid" according to the present invention may include cDNA, RNA, genomic DNA, and modified nucleic acids or nucleic acid analogs (e.g., peptide nucleic acids). For example, when a DNA sequence is specified, with reference to the Figures, RNA equivalents are encompassed, with U substituted for T, where present, unless the context otherwise requires. Nucleic acid molecules according to the present invention may be provided isolated and / or purified from their natural environment in substantially pure or homogeneous form, or free or substantially free from the species of origin and other nucleic acids, double-stranded or single-stranded. As used herein, the term "isolated" encompasses all of these possibilities. Nucleic acid molecules may be wholly or partially synthetic. In particular, they may be recombinant, in that nucleic acid sequences not found together in nature (not a contiguous stretch) have been ligated or otherwise artificially combined. Nucleic acids may comprise, consist of, or consist essentially of any of the sequences described herein below.

[0156] The term "heterologous" is used broadly herein to indicate that the nucleotide gene / sequence in question (e.g., encoding a QA biosynthetic modified polypeptide) has been introduced into said cell of the host or its ancestor using genetic engineering, i.e., by human intervention. Nucleic acid heterologous to a host cell does not naturally occur in cells of that type, variety, or species. Thus, heterologous nucleic acid may comprise or be derived from a coding sequence of a particular type of plant cell or plant species or variety placed in the context of a different type of plant cell or plant species or variety. A further possibility is for the nucleic acid sequence to be placed within a cell in which it or a homologue is naturally found, but which nucleic acid sequence is linked and / or adjacent to nucleic acid that does not naturally occur in that cell or cells of that type or plant species or variety, and which is operably linked to one or more regulatory sequences, such as, for example, a promoter sequence, for control of expression.

[0157] "Transformed" in this context means that the nucleotide sequence of the heterologous nucleic acid alters one or more of the characteristics, and thus the phenotype, of the cell, e.g., with respect to QA biosynthesis. Such transformation may be transient or stable.

[0158] By "incapable of QA biosynthesis" is meant that prior to conversion, the host does not naturally produce, or is not expected to produce, detectable or recoverable levels of QA under the host's normal metabolic environment.

[0159] The nucleotide sequence information provided herein can be used to design probes and primers for probing or amplification. Oligonucleotides for use in probing or PCR can be about 30 or fewer nucleotides in length (e.g., 18, 21, or 24). Generally, specific primers are greater than 14 nucleotides in length. For optimal specificity and cost-effectiveness, primers 16 to 24 nucleotides in length may be preferred. Those skilled in the art are familiar with designing primers for use in processes such as PCR. If desired, probing can be performed using entire restriction fragments of the genes disclosed herein, which may be 100 or even 1,000 nucleotides in length. If necessary, slight variations can be introduced into the sequence to generate "consensus" or "degenerate" primers.

[0160] Probing can utilize standard Southern blotting techniques. For example, DNA can be extracted from cells and digested with different restriction enzymes. Restriction fragments can then be separated by electrophoresis on an agarose gel before denaturation and transferred to a nitrocellulose filter. Labeled probes can be hybridized to the single-stranded DNA fragments on the filter, and binding can be determined. DNA for probing can be prepared from RNA preparations derived from cells. Probing can optionally be performed using so-called "nucleic acid chips" (for a review, see Marshall & Hodgson (1998) Nature Biotechnology 16: 27-31).

[0161] In one embodiment, variants encoding QA biosynthetic modified polypeptides according to the present invention can be obtained by a method comprising: (a) preparing a nucleic acid preparation, for example, from a plant cell. The test nucleic acid may be prepared from the cell as genomic DNA, cDNA, or RNA, or a mixture of any of these, preferably as a library in a suitable vector. When genomic DNA is used, probes may be used to identify non-transcribed regions of genes (e.g., promoters, etc.), as described herein below. (b) providing a nucleic acid molecule that is a probe or primer as described above; (c) contacting the nucleic acid in the preparation with the nucleic acid molecule under conditions for hybridization of the nucleic acid molecule with any of the genes or homologs in the preparation; and (d) identifying the gene or homologue, if present, by its hybridization with the nucleic acid molecule. Binding of the probe to the target nucleic acid (e.g., DNA) can be measured using any of a variety of techniques at the disposal of those skilled in the art. For example, the probe may be radioactively labeled, fluorescently labeled, or enzymatically labeled. Other methods that do not utilize probe labeling include PCR (see below), amplification using RNase cleavage, and allele-specific oligonucleotide probing. Identification of successful hybridization is followed by isolation of the hybridized nucleic acid, which may involve one or more steps of PCR or amplification of the vector in a suitable host.

[0162] Preliminary experiments can be performed by hybridizing under low stringency conditions. For probing, preferred conditions are those that are sufficiently stringent that there is a simple pattern of a small number of hybridizations identified as positive, which can then be further investigated.

[0163] For example, hybridization can be performed according to the method of Sambrook et al. (infra) using a hybridization solution containing 5x SSC (here, "SSC" = 0.15 M sodium chloride; 0.15 M sodium citrate; pH 7), 5x Denhardt's reagent, 0.5-1.0% SDS, 100 μg / ml denatured, fragmented salmon sperm DNA, 0.05% sodium pyrophosphate, and up to 50% formamide. Hybridization is performed at 37-42°C for at least 6 hours. After hybridization, filters are washed as follows: (1) 2x SSC and 1% SDS at room temperature for 5 minutes; (2) 2x SSC and 0.1% SDS at room temperature for 15 minutes; (3) 1x SSC and 1% SDS at 37°C for 30 minutes to 1 hour; and (4) 1x SSC and 1% SDS at 42-65°C for 2 hours, with the solution changed every 30 minutes.

[0164] One common formula for calculating the stringency conditions required to achieve hybridization between nucleic acid molecules with specific sequence homology is (Sambrook et al., 1989): m = 81.5°C + 16.6 Log[Na+] + 0.41(G+C%) - 0.63(formamide%) - 600 / # bp in the duplex.

[0165] As an example of the above formula, using [Na+]=[0.368] and 50% formamide with 42% GC content and an average probe size of 200 bases, T m The T of a DNA duplex is 57°C. m The temperature decreases by 1-1.5°C for every 1% decrease in homology. Thus, targets with greater than about 75% sequence identity are observed using a hybridization temperature of 42°C. Such sequences are considered to be substantially homologous to the nucleic acid sequences of the present invention.

[0166] It is well known in the art to gradually increase the stringency of hybridization until only a few positive clones remain. Other suitable conditions include, for example, for detection of sequences with approximately 80-90% identity, overnight hybridization at 42°C in 0.25M NaHPO, pH 7.2, 6.5% SDS, 10% dextran sulfate, with a final wash at 55°C in 0.1×SSC, 0.1% SDS. For detection of sequences with greater than approximately 90% identity, suitable conditions include overnight hybridization at 65°C in 0.25M NaHPO, pH 7.2, 6.5% SDS, 10% dextran sulfate, with a final wash at 60°C in 0.1×SSC, 0.1% SDS.

[0167] In a further embodiment, the hybridization of a nucleic acid molecule with a variant can be determined or identified indirectly, for example, by using a nucleic acid amplification reaction, particularly a polymerase chain reaction (PCR). PCR requires the use of two primers to specifically amplify a target nucleic acid, and therefore preferably utilizes two nucleic acid molecules having sequences characteristic of the QA gene of the present invention. Using RACE PCR, only one such primer may be required (see "PCR protocols; A Guide to Methods and Applications," Eds. Innis et al., Academic Press, New York, (1990)).

[0168] Thus, methods involving the use of PCR in obtaining nucleic acids according to the present invention may include: (a) providing a preparation of plant nucleic acid, e.g., from a seed or other suitable tissue or organ; (b) providing a pair of nucleic acid molecule primers useful (i.e., suitable) for PCR, at least one of which is a primer according to the invention as described above; (c) contacting the nucleic acids in the preparation with the primers under conditions for performing PCR; (d) performing PCR and determining the presence or absence of an amplified PCR product, the presence of which may indicate the identity of the variant.

[0169] In all of the above cases, clones or fragments identified in the investigation can be extended if necessary. For example, if they are suspected to be incomplete, the original DNA source (e.g., clone library, mRNA preparation, etc.) can be reexamined to isolate the missing portion, for example, using sequences, probes, or primers based on the portion already obtained to identify other clones containing overlapping sequences.

[0170] For example, a purified protein according to the invention recombinantly produced by expression from an encoding nucleic acid therefor, or a fragment, mutant, derivative or variant thereof, can be used to raise antibodies using techniques that are standard in the art. Antibodies and polypeptides, including antigen-binding fragments of antibodies, can be used in identifying homologs from other species, as further described below.

[0171] Methods for producing antibodies include immunizing a mammal (e.g., human, mouse, rat, rabbit, horse, goat, sheep, or monkey) with the protein or a fragment thereof. Antibodies can be obtained from the immunized animal using any of a variety of techniques known in the art and preferably screened using antibody binding to the antigen of interest. For example, Western blotting techniques or immunoprecipitation can be used (Armitage et al, 1992, Nature 357: 80-82). Antibodies can be polyclonal or monoclonal.

[0172] As an alternative or supplement to immunizing a mammal, antibodies of appropriate binding specificity can be obtained from recombinantly produced libraries of immunoglobulin variable domains expressed, for example, using lambda or filamentous bacteriophage which display functional immunoglobulin binding domains on their surface; see, e.g., WO 92 / 01047.

[0173] Antibodies raised against polypeptides or peptides can be used to identify and / or isolate homologous polypeptides and then the encoding genes.

[0174] Antibodies can be modified in many ways. Indeed, the term "antibody" should be interpreted to encompass any specific binding substance having a binding domain with the required specificity. Thus, the term encompasses antibody fragments, derivatives, functional equivalents, and homologs of antibodies, including any polypeptide, whether natural or synthetic, that contains an immunoglobulin binding domain.

[0175] Numerous patents and publications are cited herein to more fully describe and disclose the present invention and the state of the art to which it pertains. Each of these references is herein incorporated by reference in its entirety into the present disclosure to the same extent as if each individual reference was specifically and individually indicated to be incorporated by reference.

[0176] Throughout this specification, including the claims that follow, unless the context requires otherwise, the word "comprise" and variations such as "comprises" and "comprising" will be understood to indicate the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0177] It must be noted that as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, reference to a "pharmaceutical carrier" includes mixtures of two or more such carriers, and the like.

[0178] Ranges are often expressed herein as from "about" one particular value and / or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations, by use of "about," it will be understood that the particular value forms another embodiment.

[0179] Any subheadings herein are included for convenience only and should not be construed as limiting the disclosure in any way.

[0180] The invention will now be further described with reference to the following non-limiting figures and examples, in light of which other embodiments of the invention will occur to those skilled in the art.

[0181] The disclosures of all references cited herein, insofar as they may be used by those skilled in the art to practice the present invention, are hereby specifically incorporated by cross-reference. [Brief explanation of the drawings]

[0182] [Figure 1] FIG. 1 shows QS-21. [Figure 2] Figure 11 shows the production of quilacic acid from a common, universal precursor via β-amyrin. The pathway from β-amyrin requires oxidation at three positions (C-16α, C-23, and C-28). These oxidation steps are shown linearly for simplicity's sake, but as explained above, they can in principle proceed in other orders (see Figure 11). [Figure 3] Figure 1 shows PCR amplification of candidate genes in leaf (L) and root (R) tissues of Q. saponaria. It was possible to obtain products for most candidates in both tissues. [Figure 4] Figure 1 shows the expression of Q. saponaria β-amyrin synthase (QsbAS) in Nicotiana benthamiana. GC-MS analysis of leaf extracts reveals the production of only β-amyrin in leaves expressing the cloned β-amyrin synthase, but not in control (GFP) leaves. [Figure 5]Figure 5 shows the conversion of β-amyrin by P450s from Q. saponaria. Two P450s in the CYP716 family were found to oxidize β-amyrin. Left: GC-MS analysis of Nicotiana benthamiana leaf extract showing that CYP716-2073932 converted the majority of β-amyrin to a novel product identified as oleanolic acid at 12.08 min. The mass spectrum for this product relative to an authentic oleanolic acid standard is shown on the right. CYP716-2012090 (both long and short isoforms) converted a small amount of β-amyrin, putatively identified as 16α-hydroxy-β-amyrin (marked with an *). The mass spectrum for this product is shown in Figure 5s. [Figure 5s] EI mass spectrum for putative 16α-hydroxy-β-amyrin. Minor amounts of this product were formed upon co-expression of QsbAS and CYP716-2012090. [Figure 6A] Figure 1 shows the conversion of oleanolic acid to echinocystic acid by CYP716-2012090. Left: GC-MS analysis of Nicotiana benthamiana leaf extract showing that co-expression of two CYP716 members from Q. saponaria with QsbAS and CYP716-2073932 results in the accumulation of a product identified as echinocystic acid at 12.42 min. The mass spectrum for this compound relative to an authentic echinocystic acid standard is shown on the right. [Figure 6B] Figure 1 shows the conversion of oleanolic acid to hederagenin by OQHZ-2018687. C-23 oxidase candidates were screened for oleanolic acid oxidation activity. It was found that a novel product was observed in samples expressing candidates #6 and #7 (which possess the same enzyme, also referred to herein as CYP714-7). This novel product had the same retention time and mass spectrum as a 23-hydroxy-oleanolic acid (hederagenin) standard, suggesting that this enzyme is a C-23 oxidase. [Figure 7]Figure 1 shows LC-MS analysis of Nicotiana benthamiana leaf extracts expressing a combination of QsbAS and the C-28 (CYP716-2073932), C-16α (CYP716-2012090), and C-23 (CYP714-7) oxidases from Q. saponaria. Queric acid (19.886 min) was observed only in samples expressing all three P450s. Mass spectra for various samples at 19.886 min are shown below, along with a queric acid standard. [Figure 8] Figure 1 shows a comparison of quilacic acid production among plant samples expressing different C-23 oxidases. All samples were derived from leaves expressing tHMGR, QsbAS, and Q. saponaria C-28 (CYP716-2073932) and C-16α (CYP716-2012090) oxidases. The C-23 oxidases were derived from either Q. saponaria (CYP714-7, top), M. truncatula (CYP72A68, bottom second), or A. strigosa (CYP94D65, bottom third). CAD chromatograms are shown at the top. Mass spectra of interest (negative mode) are shown at the bottom. A common ion with m / z 485 (shown in red) was common to both the quillaric acid standard and the new peak in the tHMGR / QsbAS / CYP716-2073932 / CYP716-2012090 / CYP94D65 sample. This ion matches the predicted molecular weight (minus H) of quillaric acid. *A second compound was found at high abundance with m / z 487 that was putatively identified as cauphyllogenin (featuring a C-23 alcohol instead of an aldehyde as found in quillaric acid). Mass spectra for these products are shown in Figure 8s. Lesser amounts of other C-23 oxidation by-products, including a C-23 alcohol (cauphylogenin) and an acid (16α-hydroxy-gypsogenic acid (16OH-GA)), were found in the Q. saponaria C-23 expression sample, suggesting a higher specificity for aldehyde production. [Figure 9]Figure 1 shows the expression of Q. saponaria genes in yeast. GC-MS traces are shown for different strains at the top and mass spectra for the peaks of interest at the bottom. [Figure 10] A) A simplified overview of the mevalonate (MVA) pathway and potential rate-limiting enzymes required for triterpene biosynthesis. B) β-amyrin content in Nicotiana benthamiana can be improved from co-expression of tHMGR or SQS with oat β-amyrin synthase (AsbAS). C) Co-expression of SQS with tHMGR further improves β-amyrin content over tHMGR alone. [Figure 11] FIG. 1 shows oxidized derivatives of β-amyrin. [Figure 12]

[0033] Figure 1. Biosynthesis of quillaric acid from 2,3-oxidosqualene and related enzymes from Q. saponaria. The oxidation steps do not have to occur in exactly this order. [Figure 13] LC-CAD analysis of a representative leaf expressing the four signature enzymes from Q. saponaria required to make quillic acid (top), while as a control, C-16 alpha oxidase was omitted (bottom), resulting in the accumulation of the precursor gypsogenin instead (see Figure 12). [Figure 14] Figure 1 shows LC analysis of isolated product from Nicotiana benthamiana versus quillic acid standard. A) LC-CAD trace showing analysis of isolated product (middle) and quillic acid standard (bottom). Both samples showed a major peak at 19.5 minutes. A methanol-only blank run is shown in the top trace. B) MS (ESI / APC) analysis of the product at 19.5 minutes in both positive (top) and negative (bottom) modes. The isolated product is shown on the left, and the quillic acid standard is shown on the right. [Figure 15]Figure 1 shows GC-MS analysis of quillic acid standards versus isolated product from Nicotiana benthamiana. A) The standard is shown in the lower trace, and the isolated product is shown in the upper trace. Both samples showed a major peak at 15.3 minutes. B) Comparison of EI mass spectra of the two products at 15.3 minutes. The isolated product is shown on top, and the quillic acid standard is shown on the bottom. [Figure 16] FIG. 1 shows a 1H NMR (methanol d4) comparison of quillic acid standards (bottom) against the product isolated from Nicotiana benthamiana (top). [Example]

[0183] Example 1 – Mining the Q. saponaria transcriptome for candidate quillic acid biosynthetic genes Recently, a transcriptome dataset from Q. saponaria became available through the 1KP project [1]. This dataset was derived from HiSeq sequencing (Illumina) of Q. saponaria leaf tissue.

[0184] Commercial sources of QS-21 are typically derived from bark, but leaf tissue has also been shown to be a sufficient source of QS-21 and other saponins [2], so we reasoned that relevant biosynthetic genes might be present in this database. The transcriptome dataset was mined for potential biosynthetic genes.

[0185] β-amyrin synthase The first candidate we searched for was β-amyrin synthase (bAS) OSC. We have characterized numerous bAS enzymes, including those from related Leguminosae species.

[0186] The bAS enzyme from Glycyrrhiza glabra (Genbank ID Q9MB42.1) was used as a query to identify OSC sequences, which returned a single full-length sequence (OQHZ-2074321) predicted to be a triterpene synthase (hereafter referred to as QsbAS).

[0187] Other partial OSC sequences were also identified in this dataset, but these were predicted to be sterol (cycloartenol) synthases and were discounted.

[0188] The complete nucleotide and predicted protein sequence of QsbAS is shown in Sequence Appendix A as SEQ ID NOs: 1 and 2.

[0189] β-amyrin oxidase We speculated that a likely class of enzymes involved in the oxidation of β-amyrin are cytochrome P450s (P450s), which are typically encoded by very large gene superfamilies with over 200 representatives in a single plant genome.

[0190] Although predicting function based on sequence homology is often difficult, the CYP716 family has recently emerged as a prominent family of triterpene oxidases. [3] To date, 11 CYP716s have been characterized as β-amyrin C-28 oxidases (Sequence Appendix B). These P450s were isolated from taxonomically distinct species (including those in the Leguminosae order), suggesting that the C-28 β-amyrin oxidase in Q. saponaria may be catalyzed by a member of this family.

[0191] Furthermore, CYP716 enzymes have also been shown to be capable of catalyzing oxidation at other (non-C-28) positions around the β-amyrin scaffold, including one C-16 α-oxidase (CYP716Y1) from Bupleurum falcatum (Sequence Appendix B). Two full-length CYP716s were identified in a transcriptome dataset using the Medicago truncatula C-28 oxidase CYP716A12 as a search query. These are OQHZ-2073932 and OQHZ-2012090 (sometimes referred to herein as CYP716-2073932 and CYP716-2012090).

[0192] (Note that CYP716-2073932 has also been officially designated CYP716A224 by the P450 Nomenclature Committee [3].) The complete nucleotide and predicted protein sequences of these CYP716s are shown in Sequence Appendix A as SEQ ID NOs: 3 and 4.

[0193] Example 2 – Cloning candidate genes from Q. saponaria Q. saponaria plants were obtained from a UK nursery (Burncoose Nurseries, Cornwall). RNA was extracted from the leaves and roots of a single tree using the Qiagen RNeasy Plant RNA extraction kit according to a modified protocol detailed in

[26] . This RNA was further used as a template for cDNA synthesis using Superscript III (Invitrogen) according to the manufacturer's instructions.

[0194] For amplification of the target genes, primers were designed for each of the four genes listed above (SEQ ID NOS: 1, 3, 5, and 7). For CYP716-2012090, two sets of primers were designed that allowed for cloning of both the long and short isoforms of the protein, which differ by 21 amino acids at the N-terminus. This was due to poor alignment of this region with other characterized CYP716s.

[0195] Each of the primers incorporated an attB adapter at the 5' end to allow for directional Gateway®-based cloning. These adapters are shown in italics at the 5' end, with the gene-specific sequence following in the 5'→3' direction.

[0196] [Table 2]

[0197] Two PCR reactions were performed for each gene, using either leaf or root cDNA as the template. As described above, two sets of PCRs were set up for separate reactions of CYP716-2012090 using different forward primers. PCRs were performed in a total volume of 50 μL using iProof (BioRad) with HF buffer according to the manufacturer's instructions. For amplification of the QsbAS and CYP716 enzymes, the PCR thermal cycle included an initial denaturation step at 98°C (30 s), followed by 30 cycles of denaturation (98°C, 10 s), annealing (50°C, 10 s), and extension (72°C, 3 min), with a final extension at 72°C (5 min). These parameters were identical to those for amplification of CYP714, except that the extension time during the 30 cycles was shortened to 2 min.

[0198] Successful PCR was observed for all genes using cDNA from both root and leaf tissues as PCR templates (Figure 3). PCR products derived from leaf cDNA were further purified and recombined into the pDONR207 entry vector as previously described [5]. The resulting plasmids were sequenced by Eurofins Genomics to verify the presence and sequence of the inserted genes. A single representative plasmid was selected for each gene, recombined into the binary vector pEAQ-HT-DEST1 [4], and then transformed into competent Agrobacterium tumefaciens as previously described [5]. For transient expression in Nicotiana benthamiana, A. tumefaciens strains were grown and prepared for infiltration as previously described [5, 27].

[0199] Example 3 – Transient expression of Q. saponaria genes in Nicotiana benthamiana QsbAS is a monofunctional β-amyrin synthase Transient expression of various cloned genes was performed in N. benthamiana. All combinations included co-infiltration of a strain carrying a feedback-insensitive truncated form of A. strigosa HMG-CoA reductase (tHMGR). This enzyme has been demonstrated to increase triterpene content upon transient expression in N. benthamiana [5]. The sequences utilized are shown as SEQ ID NOs: 29-32.

[0200] Leaves were harvested, extracted, and analyzed by GC-MS as previously described [5]. GC-MS analysis of QsbAS-expressing leaves revealed the presence of a compound identified as β-amyrin by comparison of its retention time and mass spectrum with a β-amyrin standard (Figure 4). No other novel products were found in the chromatogram, suggesting that QsbAS is a monofunctional β-amyrin synthase.

[0201] Discovery of C-28 and C-16 α-oxidases Next, QsbAS was tested with various P450 combinations. This revealed that both CYP716 enzymes exhibited activity toward β-amyrin. CYP716-2073932 was found to be a C-28 oxidase and converted most of the β-amyrin to oleanolic acid. CYP716-2012090 converted a small amount of β-amyrin to a product putatively identified as 16α-hydroxy-β-amyrin (based on comparison with previously published mass spectra [6, 7]) (Figure 5; Figure 5s).

[0202] Combining these two CYP716 enzymes identified a third product with a retention time and mass spectrum identical to that of β-amyrin and echinocystic acid, an intermediate of quilacic acid consisting of a C-28 carboxylic acid and a C-16 α-alcohol (Fig. 6A).

[0203] Example 4 – Discovery of a C-23 oxidase from Q. saponaria Following the discovery of the C-28 and C-16 α-oxidases, attention was focused on the prominent Q. saponaria C-23 oxidase. Identification of the C-28 and C-16 α-oxidases was facilitated by a homology-based search of known triterpene-oxidizing P450s. Other candidates were considered based on their homology to known triterpene oxidases, including two CYP72 family members (OQHZ-2012357 and OQHZ-2019977), for which a C-23 oxidase has been identified in the related legume species Medicago truncatula. However, when cloned and tested in planta, none of these candidates showed significant activity toward β-amyrin or its C-28 / C-16 α-oxidized derivatives (data not shown).

[0204] Consequently, it was speculated that the prominent Q. saponaria C-23 oxidase may be within a P450 family not previously implicated in triterpene oxidation.

[0205] Therefore, the 1KP transcriptome data was searched for all putative cytochrome P450s.

[0206] Approximately 150 P450-encoding contigs were found in the dataset, of which 35 appeared to encode full-length enzymes (approximately 1500 bp, see Table 5).

[0207] [Table 3]

[0208] Table 5: List of all 35 full-length cytochrome P450s represented in the Q. saponaria 1KP dataset. Putative families / clans were assigned based on a Genbank BLAST search. Candidates predicted to be involved in primary metabolism were not considered further. This resulted in 25 final candidates (see "Quick Reference" column). Note that the names of the candidates used here are derived from the contig counts of the independently assembled transcriptomes. This count results in a different nomenclature system than previously used for the CYP716 / CYP72 enzymes.

[0209] Among these full-length contigs were the C-28 and C-16 α-oxidases described above, and it was therefore inferred that the prominent C-23 oxidase may also be represented within these sequences.

[0210] The 35 P450 candidates were further assigned to putative clans and families based on their homology to named P450s from other species (Table 5). Many candidates were predicted to be involved in primary metabolism (and shared a high degree of sequence conservation with enzymes from unrelated species such as Arabidopsis) and were subsequently removed from the list.

[0211] This resulted in a final list of 25 candidates for which cloning primers were ordered. For ease of reference, these are numbered 1-25 in Table 5 and are described herein using these numbers.

[0212] Next, PCR amplification of the 25 candidates was attempted. As with the previous candidates, two PCRs were performed for each candidate, using cDNA templates from both the leaf (L) and root (R), respectively. Strong PCR products were successfully produced for 20 of the 25 candidates (data not shown). These were then purified (from the leaf cDNA template samples) and cloned into the Gateway® entry vector pDONR207.

[0213] Candidates were sequenced to verify that the correct gene had been cloned. In most cases, the cloned sequences closely matched the predicted sequences. Some redundancy was found among clones; the sequences of #6 and #7 were found to be identical, as were #16 and #17. Checking the predicted sequences in the original transcriptome data revealed that the contigs for these pairs were very similar, and the primers were not designed to distinguish them. Nevertheless, the clones were processed separately and cloned into the pEAQ-HT-DEST1 binary vector, which was then transformed into A. tumefaciens.

[0214] Next, 15 candidates were transiently expressed in Nicotiana benthamiana. First, the candidates were evaluated for their potential to oxidize β-amyrin by coexpression with Q. saponaria β-amyrin synthase (QsbAS). No novel products were detected in these samples by GC-MS analysis. Therefore, the candidates were further evaluated for their ability to oxidize oleanolic acid by coexpression with QsbAS and a C-28 oxidase (CYP716-2073932). In this case, distinct novel products could be detected in leaf extracts expressing candidates #6 and #7 (6 and #7 encode the same enzyme, as described above). The novel products had identical retention times and mass spectra to a standard of 23-hydroxy-oleanolic acid (also known as hederagenin). The enzyme encoded by candidate #7 is predicted to be a CYP714 family member (yet to be formally named). Prior to the currently claimed priority date, it is believed that no members of this family were reported to be triterpene oxidases. Since the priority date, other examples have been reported (e.g., Kim et al. (2018). "A Novel Multifunctional C-23 Oxidase, CYP714E19, Is Involved in Asiaticoside Biosynthesis". Plant Cell Physiol.) pp. 1200-1213.

[0215] The sequences are included in Appendix A as SEQ ID NOs:7 and 8.

[0216] Since the C-23 candidate was derived from our own assembly of this data, we searched for the corresponding sequence in the 1KP dataset using BLASTn (https: / / db.cngb.org / blast4onekp / ). Surprisingly, #7 is not represented by a full-length sequence in this database, but several smaller contigs are returned (Table 6). The top hit from these is OHQZ-2018687, an 821-bp contig.

[0217] [Table 4]

[0218] Table 6: List of contigs from the 1KP dataset returned from a BLASTn query of C-23 oxidase. The top-scoring hit is OQHZ-2018687.

[0219] Example 5 - Combinatorial biosynthesis with Q. saponaria enzymes enables the synthesis of quillic acid in Nicotiana benthamiana The β-amyrin synthase and C-28, C-16α, and C-23 oxidases from Q. saponaria described above, when expressed together, should be sufficient to produce quilacic acid (see Figure 2).

[0220] Prior to testing the C-23 oxidase from Q. saponaria, other candidate genes from Q. saponaria were combined with characterized C-23 β-amyrin oxidases from other species, namely, CYP72A68v2 from Medicago sativa (barrel medic) and CYP94D65 from Avena strigosa (black oat) (SEQ ID NOs: 13-16).

[0221] In this initial experiment, QsbAS and two CYP716 enzymes from Q. saponaria were combined with Medicago sativa and A. strigosa C-23 oxidases using transient expression in Nicotiana benthamiana to determine whether quinoline acid could be observed in these samples. LC-MS-CAD analysis revealed that quinoline acid could be detected in these samples. ·tHMGR / QsbAS / CYP716-2073932 / CYP716-2012090 / CYP72A68v2 ·tHMGR / QsbAS / CYP716-2073932 / CYP716-2012090 / CYP94D65 Both sets of combinations were found to result in the appearance of new products that matched the retention times and mass spectra of quinoline standards (results not shown).

[0222] Quillaric acid abundance appeared to be highest in samples expressing CYP72A68v2.

[0223] Other related products were also observed in these samples: in combinations expressing oat C-23 oxidase (CYP94D65), the most abundant new peak was identified as kauphylogenin (a C-23 alcohol instead of the aldehyde found in quillaric acid), whereas Medicago C-23 oxidase (CYP72A68v2) resulted in significant accumulation of 16α-hydroxygypsogenin (a C-23 carboxylic acid instead of the aldehyde found in quillaric acid).

[0224] To verify that quillic acid can be produced in N. benthamiana by exclusive use of Q. saponaria enzymes, the QsbAS enzyme was transiently expressed with various combinations of P450s. As expected, analysis of leaves coexpressing QsbAS with all P450s resulted in the appearance of a peak matching the retention time and mass spectrum of the quillic acid standard. This peak was absent in samples from leaves expressing less than the entire pathway (Figure 7).

[0225] Furthermore, a comparison was made between the present samples expressing the full Q. saponaria complement of enzymes and equivalent (preserved) samples in which C-23 oxidases from Medicago truncatula and oat were used. This revealed that the amount of quillic acid appeared to be highest in the samples expressing the Q. saponaria C-23 oxidase (Figure 8). The samples expressing the Q. saponaria C-23 oxidase also appeared to contain significantly less of the putative unwanted by-products, kauphylogenin and 16α-hydroxygypsogenic acid (Figure 8). These metabolites reflect the different C-23 oxidase specificities of the oat and Medicago enzymes, which primarily produce C-23 alcohols and acids, respectively. Thus, the Q. saponaria C-23 oxidase appears to be even more specific for C-23 aldehydes, reflecting its predicted function in QS-21 biosynthesis.

[0226] Example 6 - Expression of Q. saponaria genes in yeast Saccharomyces cerevisiae can be used as a host chassis for commercial QA production.

[0227] Thus, we demonstrated that the cloned Quillaja genes were active in this host. We used a strain of S. cerevisiae derived from S288C (genotype: MATa / MATα; ura3Δ0 / ura3Δ0; leu2Δ0 / leu2Δ0; his3Δ1 / his3Δ1; met15Δ0 / MET15; LYS2 / lys2Δ0; YHR072w / YHR072w::kanM), which contains three auxotrophic selection markers (-URA / -HIS / -LEU) that allow expression of genes from up to three plasmids.

[0228] Three Gateway-compatible yeast expression vectors were utilized, including pYES-DEST52 (uracil selection), pAG423 (histidine selection), and pAG435 (leucine selection).

[0229] Q. saponaria enzymes were recombined into these vectors as described in Table 7. Briefly, β-amyrin synthase (QsbAS) was recombined into the pYES-DEST52 vector, while C-28 oxidase (CYP716-2073932) and C-16 α-oxidase (both long (L) and short (S) isoforms) were recombined into pAG423.

[0230] To increase the functional efficiency of cytochrome P450, a third plasmid (pAG435) was used to express the Arabidopsis thaliana cytochrome P450 reductase 2 (AtATR2) enzyme, which serves as a coenzyme to reduce plant P450s back to their active state after substrate oxidation. All vectors contain a galactose-inducible promoter to express inserted genes.

[0231] [Table 5]

[0232] Table 7: List of generated yeast strains.

[0233] Yeast strains were cultured in synthetic yeast medium containing galactose and incubated at 30°C for 2 days. Strains were pelleted by centrifugation, saponified, and metabolites were extracted with ethyl acetate. GC-MS analysis revealed that all strains accumulated a peak identified as β-amyrin at 10.6 min (Figure 9). Strain 63 (expressing C-28 oxidase) was found to accumulate small amounts of additional products identified as C-28 oxidized β-amyrin derivatives, including oleanolic acid (12.01 min) and the intermediate C-28 alcohol erythrodiol (11.51 min) (Figure 9, second trace from the top). No products readily identifiable as 16-hydroxy-β-amyrin were identified in strains 64 or 65 (expressing the C-16 α-oxidase isoform), implying that they may not be optimal substrates for this enzyme.

[0234] The above data demonstrate that yeast can be engineered to produce quinoline precursors.

[0235] Example 7 - Production of QA by stable transformation Triterpenes have previously been produced using engineered transgenic plant lines (e.g., Arabidopsis, wheat). A series of Golden Gate

[23] vectors have been reported that allow the construction of multigene vectors and the integration of entire pathways into a single locus. These can be similarly applied to the present invention in light of the disclosure herein.

[0236] Example 8 - Conclusions from Examples 1-7 Quillaric acid is a triterpenoid and an important precursor of the saponin QS-21 produced by Quillaja saponaria.

[0237] Here, we identified four enzymes from Q. saponaria (β-amyrin synthase and C-16α, C-23, and C-28 oxidases) that were capable of producing quillic acid when transiently expressed in Nicotiana benthamiana. These enzymes are predicted to be involved in the early steps of the QS-21 biosynthetic pathway, required for the generation of the quillic acid scaffold (Figure 1).

[0238] The identity of the products described herein was verified by the use of authentic standards, giving a high degree of confidence in these results.

[0239] The activities of β-amyrin synthase (QsbAS) and three cytochrome P450 monooxygenases (referred to herein as CYP716-2073932, CYP714-7, and CYP716-2012090, respectively) that oxidize β-amyrin at the C-28, C-23, and C-16α positions in the biosynthesis of quilacic acid are shown schematically in Figure 12.

[0240] Example 9 – Estimation of quillic acid production in Nicotiana benthamiana To estimate quillic acid production in N. benthamiana after transient expression, LC-CAD analysis was performed. Agroinfiltration was performed as previously described using Q. saponaria β-amyrin synthase and C-16α, C-23, and C-28 oxidases. As a control, leaves infiltrated with only two oxidases (C-23 and C-28) were used, resulting in the accumulation of gypsogenin instead of quillic acid (Figure 12).

[0241] Oat HMG-CoA reductase (tHMGR) was also included in all infiltrations, as it increases the production of β-amyrin. Representative chromatograms from these samples are shown in Figure 13. Three leaves from different plants were used for each test condition as biological replicates.

[0242] To estimate the production of quillic acid in these leaves, the area of ​​the quillic acid peak was compared with that of an internal standard (contained at 1.1 mg / g dry leaf weight). The average value from three replicates was found to be 1.44 mg / g.

[0243] Example 10 – Purification of quillic acid from Nicotiana benthamiana To definitively determine that quillic acid production was achieved in Nicotiana benthamiana, product purification was performed.

[0244] A total of 209 Nicotiana benthamiana plants were vacuum-infiltrated with A. tumefaciens carrying the pEAQ-HT-DEST1 construct, which contains Q. saponaria β-amyrin synthase, C-16α, C-23, and C-28 oxidases. Oat tHMGR was also included to enhance yield. Leaves were harvested 4 days after infiltration, yielding 150.3 g of dry material after lyophilization. Metabolites were extracted with ethanol using a Buchi Speed ​​Extractor E-914, and a total of 30 mg of product was isolated using several rounds of silica gel flash chromatography. The isolated product was found to have a retention time and mass spectrum identical to that of an authentic chiral acid standard (Extrasynthese) by LC-MS (Figure 14) and GC-MS (Figure 15). Furthermore, the isolated product 1 H NMR spectroscopy was also consistent with a quinoline acid standard (Figure 16).

[0245] This confirms that quillaric acid can be produced in N. benthamiana via transient expression of the Q. saponaria enzyme. The isolated yield of the product was in the range of 0.2 mg / g dry weight, although small amounts of impurities were detected in the samples. This yield is lower than the estimated yield from LC-CAD in Example 9, indicating product loss during the isolation process. Nevertheless, this demonstrates that practical quantities of quillaric acid can be produced and isolated from N. benthamiana using the currently characterized enzyme.

[0246] method Infiltration Agroinfiltration was performed using a needleless syringe as previously described (Reed et al., 2017). All genes were expressed in A. tumefaciens LBA4404 from the pEAQ-HT-DEST1 binary expression vector (Sainsbury et al., 2009). All plants co-expressed oat tHMGR, Quillaja β-amyrin synthase (QsbAS), and β-amyrin C-28 (CYP716-2073932) and C-16α (CYP716-2012090S) oxidases. For quillaric acid production, C-23 (CYP714-7) oxidase was also co-expressed, with green fluorescent protein (GFP) used as a control. Bacterial and plant cultures were as described (Reed et al., 2017). Three plants per test condition were infiltrated and analyzed separately as biological replicates.

[0247] LC-MS analysis Leaves were collected 5 days after agroinfiltration and freeze-dried. Freeze-dried leaf material (10 mg per sample) was ground at 1000 rpm for 1 min (Geno / Grinder 2010, Spex SamplePrep). Extraction was performed in 550 μL of 80% methanol containing 20 μg / mL digitoxin (internal standard; Sigma) at 40°C for 20 min with shaking at 1400 rpm (Thermomixer Comfort, Eppendorf). Samples were partitioned twice with 400 μL of hexane. The aqueous phase was dried under vacuum at 40°C (EZ-2 Series Evaporator, Genevac). The dried material was resuspended in 75 μL of 100% methanol and filtered (0.2 μm, Spin-X, Costar) at 12,500 g for 30 s. The filtered samples were transferred to glass vials and analyzed as detailed below.

[0248] Preparation of Nicotiana benthamiana leaf extract The analysis was performed using a Prominence HPLC system equipped with a single quadrupole mass spectrometer, LCMS-2020 (Shimadzu), and a Corona Veo RS charged aerosol detector (CAD) (Dionex). Detection: MS (dual ESI / APCI ionization, DL temperature 250 °C, nebulizer gas flow rate 15 L / min, heat block temperature 400 °C, spray voltage 4.5 kV positive, -3.5 kV negative). CAD: data acquisition rate 10 Hz, filter constant 3.6 s, 925 evaporator temperature 35 °C, ion trap voltage 20.5 V. Method: Solvent A: [H2O + 0.1% formic acid]; Solvent B: [acetonitrile (CH3CN) + 0.1% formic acid]. Injection volume: 10 μL. Gradient: 15% [B] 0–1.5 min, 15%–60% [B] 1.5–26 min, 60%–100% [B] 26–26.5 min, 100% [B] 26.5–28.5 min, 100%–15% [B] 28.5–29 min, 35% [B] 29–30 min. The method was performed at a flow rate of 0.3 mL min-1 using a Kinetex column, 2.6 μm XB-C18 100 Å, 50 × 2.1 mm (Phenomenex).

[0249] Analysis of Nicotiana benthamiana leaf extract Analysis was performed using LabSolutions software (Shimadzu). To obtain an estimate of product yield, the peak area for quillaric acid (determined by CAD) was divided by the area of ​​the internal standard (digitoxin, 1.1 μg / mg dried leaf tissue). Results were averaged from three replicates. A minor peak for an endogenous N. benthamiana product with the same retention time as quillaric acid was observed in the control (calculated mean value 0.25 μg / mg). Therefore, this value was subtracted from the estimated quillaric acid yield.

[0250] Large-Scale Infiltration Agroinfiltration was performed as detailed above using tHMGR, QsbAS, CYP716-2073932, CYP716-2012090S, and CYP714-7 oxidases. A total of 209 plants were infiltrated by vacuum as previously described (Reed et al., 2017) and harvested 4 days later.

[0251] Purification of quillic acid from Nicotiana benthamiana. Leaves from the large-scale infiltration were collected and freeze-dried, and extraction was performed using a SpeedExtractor E-914 (Buchi) as detailed in (Reed et al., 2017), except that the program included four cycles (100 °C and 130 bar pressure). Cycle 1 (hexane) had a zero retention time, and cycles 2–4 (ethanol) had 5-minute retention times. The run ended with a 2-minute solvent flush and a 6-minute N2 flush. The hexane portion of the extract was discarded, and the ethanol portion was used for subsequent flash chromatography, performed using an Isolera One (Biotage) with the individual column details shown below. Fractions were checked for quinoline acid after each column by GC-MS and thin-layer chromatography (TLC) as detailed in (Reed et al., 2017). At each stage, the purest fractions were pooled and dried onto silica gel 60 (Material Harvest) for loading onto the subsequent column. Column 1: SNAP Ultra 50 g (Biotage), flow rate: 100 mL / min, 90 mL fractions with the following gradient: Solvent A: [hexane] Solvent B: [ethyl acetate]; gradient: 5% [B] to 100% [B] over 10 column volumes, held at 100% [B] for an additional 5 column volumes. Column 2: SNAP Ultra 50 g column (Biotage), flow rate: 100 mL / min, 90 mL fractions with the following gradient: Solvent A: [dichloromethane] Solvent B: [ethyl acetate]; gradient: 10% [B] to 60% [B] over 10 column volumes, held at 100% [B] for an additional 2 column volumes. Column 3: SNAP Ultra 10 g (Biotage), flow rate: 36 mL / min, 17 mL fractions with the same gradient as column 2. After column 3, the fractions were treated with activated carbon to remove colored impurities and loaded onto column 4. Column 4: SNAP Ultra 10 g column (Biotage) using an isocratic mobile phase of 15% ethyl acetate in dichloromethane over 20 column volumes (36 mL / min, 17 mL fractions). Pooled fractions were treated with a small amount of HCl (400 μL of concentrated HCl in approximately 40 mL of ethanol) to help reduce streaking on the TLC plate.Column 5: SNAP Ultra 10 g column (Biotage) (36 mL / min, 17 mL fractions) using an isocratic mobile phase of 15% ethyl acetate in dichloromethane over 30 column volumes, with a final flush of 100% ethyl acetate over 5 column volumes. The purest fractions were pooled and dried to give 30 mg of a white powder containing a small amount of yellow impurity, which was analyzed by GC-MS, LC-MS, and NMR as follows:

[0252] GC-MS, LC-MS and NMR analysis of purified quillic acid. GC-MS analysis was performed as described in (Reed et al., 2017). LC-MS analysis was performed as described above for querric acid quantification. NMR spectra were obtained by eluting querric acid in deuterated methanol. 1 H NMR was recorded in Fourier transform mode at a nominal frequency of 400 MHz. For each analytical method, a chiral acid standard (Extrasynthese) was used for comparison.

[0253] Materials and Methods References Reed J, Stephenson MJ, Miettinen K, Brouwer B, Leveau A, Brett P, Goss RJM, Goossens A, O'Connell MA, Osbourn A. 2017. A translational synthetic biology platform for rapid access to gram-scale quantities of novel drug-like molecules. Metab Eng 42: 185-193. Sainsbury F, Thuenemann EC, Lomonossoff GP. 2009. pEAQ: versatile expression vectors for easy and quick transient expression of heterologous proteins in plants. Plant Biotechnol J 7(7): 682-693.

[0254] Other references 1. Johnson, M.T.J., et al., Evaluating Methods for Isolating Total RNA and Predicting the Success of Sequencing Phylogenetically Diverse Plant Transcriptomes. PLOS ONE, 2012. 7(11): p. e50226. 2. Schlotterbeck, T., et al., The Use of Leaves from Young Trees of Quillaja saponaria (Molina) Plantations as a New Source of Saponins. Economic Botany, 2015. 69(3): p. 262-272. 3. Miettinen, K., et al., The ancient CYP716 family is a major contributor to the diversification of eudicot triterpenoid biosynthesis. Nat Commun, 2017. 8: p. 141�3. 4. Sainsbury, F., E.C. Thuenemann, and G.P. Lomonossoff, pEAQ: versatile expression vectors for easy and quick transient expression of heterologous proteins in plants. Plant Biotechnol J, 2009. 7(7): p. 682-93. 5. Reed, J., et al., A translational synthetic biology platform for rapid access to gram-scale quantities of novel drug-like molecules. Metab Eng, 2017. 6. Moses, T., et al., Combinatorial biosynthesis of sapogenins and saponins in Saccharomyces cerevisiae using a C-16α hydroxylase from Bupleurum falcatum. Proc Natl Acad Sci U S A, 2014. 111(4): p. 1634-39. 7. Moses, T., et al., Unravelling the Triterpenoid Saponin Biosynthesis of the African Shrub Maesa lanceolata. Mol Plant, 2014. 8: p. 122-35. 8. Fukushima, E.O., et al., Combinatorial biosynthesis of legume natural and rare triterpenoids in engineered yeast. Plant Cell Physiol, 2013. 54(5): p. 740-9. 9. Fukushima, E.O., et al., CYP716A subfamily members are multifunctional oxidases in triterpenoid biosynthesis. Plant Cell Physiol, 2011. 52(12): p. 2050-61. 10. Carelli, M., et al., Medicago truncatula CYP716A12 is a multifunctional oxidase involved in the biosynthesis of hemolytic saponins. Plant Cell, 2011. 23(8): p. 3070-81. 11. Han, J.Y., et al., The involvement of β-amyrin 28-oxidase (CYP716A52v2) in oleanane-type ginsenoside biosynthesis in Panax ginseng. Plant Cell Physiol, 2013. 54(12): p. 2034-46. 12. Fiallos-Jurado, J., et al., Saponin determination, expression analysis and functional characterization of saponin biosynthetic genes in Chenopodium quinoa leaves. Plant Sci, 2016. 250: p. 188-97. 13. Khakimov, B., et al., Identification and genome organization of saponin pathway genes from a wild crucifer, and their use for transient production of saponins in Nicotiana benthamiana. Plant J, 2015. 84(3): p. 478-90. 14. Andre, C.M., et al., Multifunctional oxidosqualene cyclases and cytochrome P450 involved in the biosynthesis of apple fruit triterpenic acids. New Phytol, 2016. 211(4): p. 1279-94. 15. Huang, L., et al., Molecular characterization of the pentacyclic triterpenoid biosynthetic pathway in Catharanthus roseus. Planta, 2012. 236(5): p. 1571-81. 16. Xu, G., et al., A novel glucuronosyltransferase has an unprecedented ability to catalyse continuous two-step glucuronosylation of glycyrrhetinic acid to yield glycyrrhizin. New Phytologist, 2016. 212(1): p. 123-135. 17. Shibuya, M., et al., Identification and characterization of glycosyltransferases involved in the biosynthesis of soyasaponin I in Glycine max. FEBS Lett, 2010. 584(11): p. 2258-64. 18. Wang, P., et al., Synthesis of the potent immunostimulatory adjuvant QS-21A. J Am Chem Soc, 2005. 127(10): p. 3256-7. 19. Moses, T., et al., Comparative analysis of CYP93E proteins for improved microbial synthesis of plant triterpenoids. Phytochemistry, 2014. 108: p. 47-56. 20. Dai, Z., et al., Producing aglycons of ginsenosides in bakers' yeast. Sci Rep, 2014. 4: p. 3698. 21. Dai, Z., et al., Metabolic engineering of Saccharomyces cerevisiae for production of ginsenosides. Metab Eng, 2013. 20(0): p. 146-56. 22. Salmon, M., et al., A conserved amino acid residue critical for product and substrate specificity in plant triterpene synthases. Proc Natl Acad Sci U S A, 2016. 113(30): p. E4407-14. 23. Engler, C., et al., A golden gate modular cloning toolbox for plants. ACS Synth Biol, 2014. 3(11): p. 839-43. 24. Mugford, S.T., et al., Modularity of plant metabolic gene clusters: a trio of linked genes that are collectively required for acylation of triterpenes in oat. Plant Cell, 2013. 25(3): p. 1078-92. 25. Paddon, CJ, et al., High-level semi-synthetic production of the potent antimalarial artemisinin. Nature, 2013. 496(7446): p. 528-32. 26. MacKenzie, DJ, et al., Improved RNA Extraction from Woody Plants for the Detection of Viral Pathogens by Reverse Transcription-Polymerase Chain Reaction. Plant Disease, 1997. 81(2): p. 222-226. 27. Sainsbury, F. and GP Lomonossoff, Transient expressions of synthetic biology in plants. Current Opinion in Plant Biology, 2014. 19(0): p. 1-7.

[0255] Appendix A: Sequence Listing and Sequences Table 1-Q. Saponaria Sequence Clone number refers to the number of contigs from the original 1KP transcriptome assembly (https: / / db.cngb.org / blast4onekp / ).

[0256] [Table 6]

[0257] Table 2 - Non-Q. saponaria sequences Cytochrome P450s that oxidize β-amyrin (or its derivatives) at the relevant positions (16α, 28, 23) found in chiral acids. Enzymes named in bold were tested by transient expression in Nicotiana benthamiana and found to produce products consistent with those reported by the referenced studies.

[0258] The first preceding gene name indicates the species as follows: As - Avena strigosa, At - Arabidopsis thaliana, Bf - Bupleurum falcatum, Bv - Barbarea vulgaris, Cq - Chenopodium quinoa, Cr - Catharanthus roseus, Md - Malus domestica, Ml - Maesa lanceolata, Mt - Medicago sativa, Pg - Panax ginseng, Vv - Vitis vinifera.

[0259] [Table 7]

[0260] [Table 8]

[0261] [Table 9]

[0262] [Table 10]

[0263] Table 3 - Accessory enzymes

[0264] [Table 11]

[0265] Table 4 - Comparison of gene sequences found in the 1KP dataset with sequenced clones obtained by PCR from Q. saponaria plants in this disclosure

[0266] [Table 12]

[0267] Table 8 Pairwise alignment of 18 P450s was performed using Clustal Omega (version 1.2.4 - accessed via https: / / www.ebi.ac.uk). Numbers in the table represent the percentage amino acid identity between genes. Sequences are organized according to function, with Q. saponaria genes characterized herein shown in bold. All pairwise values ​​are represented twice, and therefore redundant sequences are shown in the upper right corner of the table with a gray background. The table has been split into two pages for ease of presentation.

[0268] [Table 13]

[0269] Table 8 (continued)

[0270] [Table 14]

[0271] SEQ ID NO:1 - Q. Saponaria β-amyrin synthase, QsbAS (OQHZ-2074321) coding sequence (2277 bp):

[0272] [ka]

[0273] SEQ ID NO:2 - QsbAS (OQHZ-2074321) translated nucleotide sequence (758 aa):

[0274] [ka]

[0275] SEQ ID NO:3 - QsCYP716_2073932 (OQHZ-2073932) (C-28 oxidase previously designated CYP716A224 [3]) coding sequence (1443 bp):

[0276] [ka]

[0277] SEQ ID NO:4 - QsCYP716_2073932 (OQHZ-2073932) translated nucleotide sequence (480 aa):

[0278] [ka]

[0279] SEQ ID NO:5 - QsCYP716_2012090 (OQHZ-2012090) (C-16 alpha oxidase) coding sequence (1506 bp / 1443 bp): The long and short isoforms of NB described herein are distinguished by the presence of the first 63 nucleotides (21 amino acids) which are underlined in the sequence below.

[0280] [ka]

[0281] SEQ ID NO:6 - QsCYP716_2073932 translated nucleotide sequence (501 aa / 480 aa):

[0282] [ka]

[0283] SEQ ID NO:7 - QsCYP714_c36368 (C-23 candidate #7) coding sequence (1524 bp):

[0284] [ka]

[0285] SEQ ID NO:8 - QsCYP714_c36368 (C-23 candidate #7) translated nucleotide sequence (507 aa):

[0286] [ka]

[0287] SEQ ID NO: 9; BfCYP716Y1 (Bupleurum falcatum C-16 alpha oxidase) coding sequence (1437 bp):

[0288] [ka]

[0289] SEQ ID NO: 10; BfCYP716Y1 (Bupleurum falcatum C-16 alpha oxidase) coding sequence (478 aa):

[0290] [ka]

[0291] SEQ ID NO: 11; MlCYP87D16 (Maesa lanceolata C-16 α oxidase) coding sequence (1428 bp):

[0292] [ka]

[0293] SEQ ID NO: 12; MlCYP87D16 (Maesa lanceolata C-16 α-oxidase) coding sequence (475 aa):

[0294] [ka]

[0295] SEQ ID NO: 13; MtCYP72A68v2 (Medicago sativa C-23 oxidase) coding sequence (1563 bp):

[0296] [ka]

[0297] SEQ ID NO: 14; MtCYP72A68v2 (Medicago sativa C-23 oxidase) translated nucleotide sequence (520 aa):

[0298] [ka]

[0299] SEQ ID NO: 15; AsCYP94D65 (Awena strigosa C-23 oxidase) coding sequence (1551 bp):

[0300] [ka]

[0301] SEQ ID NO: 16; AsCYP94D65 (Awena strigosa C-23 oxidase) translated nucleotide sequence (516 aa):

[0302] [ka]

[0303] SEQ ID NO: 17; MtCYP716A12 (Medicago sativa C-28 oxidase) coding sequence (1440 bp):

[0304] [ka]

[0305] SEQ ID NO: 18; MtCYP716A12 (Medicago sativa C-28 oxidase) coding sequence (479 aa):

[0306] [ka]

[0307] SEQ ID NO: 29; AsHMGR (Awena strigosa HMG-CoA reductase) coding sequence (1689 bp): NB: The full-length HMGR sequence is provided below. The 5' region (underlined) can be removed to generate a truncated feedback-insensitive form (tHMGR). The sequence for tHMGR is also shown separately below.

[0308] [ka]

[0309] SEQ ID NO: 30; AsHMGR (Awena strigosa HMG-CoA reductase) translated nucleotide sequence (562 aa):

[0310] [ka]

[0311] SEQ ID NO: 31; AstHMGR (Avena strigosa truncated HMG-CoA reductase) coding sequence (1275 bp):

[0312] [ka]

[0313] SEQ ID NO: 32; AstHMGR (Avena strigosa truncated HMG-CoA reductase) translated nucleotide sequence (424 aa):

[0314] [ka]

[0315] SEQ ID NO: 33; AsSQS (Awena strigosa squalene synthase) coding sequence (1212 bp):

[0316] [ka]

[0317] SEQ ID NO: 34; AsSQS (Awena strigosa squalene synthase) translated nucleotide sequence (403 aa):

[0318] [ka]

[0319] SEQ ID NO: 35; AtATR2 (Arabidopsis thaliana cytochrome P450 reductase 2) coding sequence (2325 bp):

[0320] [ka]

[0321] SEQ ID NO: 36; AtATR2 (Arabidopsis thaliana cytochrome P450 reductase 2) translated nucleotide sequence (774 aa):

[0322] [ka]

Claims

1. A recombinant vector for producing quilacic acid (QA) in a host cell comprising a QA nucleotide sequence, the QA nucleotide sequence comprising: (i) SEQ ID NO: 2 (β-amyrin synthase (bAS)), SEQ ID NO: 4 (CYP450 C-28 oxidase), SEQ ID NO: 6 (CYP450 C-16α oxidase) or encoding SEQ ID NO:8 (CYP450 C-23 oxidase); (ii) encodes a variant sequence that is a homologous variant of any of SEQ ID NOs: 2, 4, 6 or 8, which shares at least 90% identity with those sequences and shares their biological activity; and / or (iii) selected from SEQ ID NO: 1, 3, 5, or 7; the biological activity of the bAS is the cyclization of 2,3-oxidosqualene (OS) to a triterpene; the biological activity of the C-28 oxidase is the oxidation of β-amyrin or an oxidized derivative thereof at the C-28 position to a carboxylic acid; the biological activity of the C-16α oxidase is the oxidation of β-amyrin or an oxidized derivative thereof at the C-16α position to an alcohol; and the biological activity of the C-23 oxidase is the oxidation of β-amyrin or an oxidized derivative thereof at the C-23 position to an aldehyde; A recombinant vector for producing QA in a host cell.

2. A recombinant vector for producing QA in a host cell as described in claim 1, wherein the QA nucleotide sequence encodes a derivative of the amino acid sequence shown in SEQ ID NO: 2, 4, 6 or 8 by addition, insertion, deletion or substitution of one or more amino acids.

3. the QA nucleotide sequence shares at least 90% identity with SEQ ID NO:2 and encodes a variant sequence that is a homologous variant of the amino acid sequence set forth in SEQ ID NO:2, capable of cyclizing 2,3-oxidosqualene (OS) to a triterpene; A recombinant vector for producing QA in the host cell of claim 1 or 2.

4. The QA nucleotide sequence shares at least 90% identity with SEQ ID NO: 4 and encodes a variant sequence that is a homologous variant of the amino acid sequence set forth in SEQ ID NO: 4, capable of oxidizing β-amyrin or an oxidized derivative thereof to a carboxylic acid at the C-28 position. A recombinant vector for producing QA in the host cell of claim 1 or 2.

5. The QA nucleotide sequence shares at least 90% identity with SEQ ID NO:6 and encodes a variant sequence that is a homologous variant of the amino acid sequence set forth in SEQ ID NO:6, capable of oxidizing β-amyrin or an oxidized derivative thereof to an alcohol at the C-16 α position. A recombinant vector for producing QA in the host cell of claim 1 or 2.

6. the QA nucleotide sequence shares at least 90% identity with SEQ ID NO:8 and encodes a variant sequence that is a homologous variant of the amino acid sequence set forth in SEQ ID NO:8, capable of oxidizing β-amyrin or an oxidized derivative thereof to an aldehyde at the C-23 position; A recombinant vector for producing QA in the host cell of claim 1 or 2.

7. The QA nucleotide sequence encodes the bAS amino acid sequence shown in SEQ ID NO:

2. A recombinant vector for producing QA in the host cell of claim 1.

8. The QA nucleotide sequence encodes the CYP450 C-28 oxidase amino acid sequence shown in SEQ ID NO:

4. A recombinant vector for producing QA in the host cell of claim 1.

9. The QA nucleotide sequence encodes the CYP450 C-16 alpha oxidase amino acid sequence shown in SEQ ID NO:

6. A recombinant vector for producing QA in the host cell of claim 1.

10. The QA nucleotide sequence encodes the CYP450 C-23 oxidase amino acid sequence set forth in SEQ ID NO:

8. A recombinant vector for producing QA in the host cell of claim 1.

11. The QA nucleotide sequence is derived from Q. saponaria. A recombinant vector for producing QA in the host cell of claim 1.

12. A recombinant vector for producing QA in a host cell according to any one of claims 1 to 11, wherein the QA nucleotide sequence is operably linked to a promoter for transcription in the host cell.

13. The recombinant vector for producing QA in a host cell according to claim 12, wherein the vector is a plant vector or a microbial vector.

14. 12. An isolated polypeptide encoded by a QA nucleotide sequence according to any one of claims 1 to 11.

15. A host cell which is a plant cell harboring within its chromosome a recombinant vector according to any one of claims 1 to 11.

16. A method for producing QA in a host cell, comprising expressing in said cell a recombinant vector according to any one of claims 1 to 11.

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