title: A genomics approach to the early stages of triterpene saponin biosynthesis in Medicago truncatula.
abstract: The saponins of the model legume Medicago truncatula are glycosides of at least five different triterpene aglycones: soyasapogenol B, soyasapogenol E, medicagenic acid, hederagenin and bayogenin. These aglycones are most likely derived from beta-amyrin, a product of the cyclization of 2,3-oxidosqualene. Mining M. truncatula EST data sets led to the identification of sequences putatively encoding three early enzymes of triterpene aglycone formation: squalene synthase (SS), squalene epoxidase (SE), and beta-amyrin synthase (beta-AS). SS was functionally characterized by expression in Escherichia coli, two forms of SE by complementation of the yeast erg1 mutant, and beta-AS by expression in yeast. Beta-amyrin was the sole product of the cyclization of squalene epoxide by the recombinant M. truncatulabeta-AS, as judged by GC-MS and NMR. Transcripts encoding beta-AS, SS and one form of SE were strongly and co-ordinately induced, associated with accumulation of triterpenes, upon exposure of M. truncatula cell suspension cultures to methyl jasmonate. Sterol composition remained unaffected by jasmonate treatment. Molecular verification of induction of the triterpene pathway in a cell culture system provides a new tool for saponin pathway gene discovery by DNA array-based approaches.
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Suzuki
authors.forename: Lahoucine
authors.initials: L
authors.lastname: Achnine
authors.forename: Ran
authors.initials: R
authors.lastname: Xu
authors.forename: Seiichi P T
authors.initials: SP
authors.lastname: Matsuda
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D000085:Acetates / Q000494:pharmacology; D000595:Amino Acid Sequence; D002240:Carbohydrate Sequence; D002478:Cells, Cultured; D003517:Cyclopentanes / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics; D020224:Expressed Sequence Tags; D013186:Farnesyl-Diphosphate Farnesyltransferase / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D023281:Genomics; D019751:Intramolecular Transferases / Q000235:genetics / Q000378:metabolism; D029902:Medicago / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009828:Oleanolic Acid / Q000031:analogs & derivatives; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism; D054883:Oxylipins; D010802:Phylogeny; D010840:Phytosterols / Q000096:biosynthesis; D012503:Saponins / Q000096:biosynthesis* / Q000737:chemistry; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D050603:Squalene Monooxygenase; D014315:Triterpenes / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000085:Acetates; D003517:Cyclopentanes; D054883:Oxylipins; D010840:Phytosterols; D012503:Saponins; D014315:Triterpenes; D009828:Oleanolic Acid; C072239:methyl jasmonate; D010105:Oxygenases; D050603:Squalene Monooxygenase; D013186:Farnesyl-Diphosphate Farnesyltransferase; D019751:Intramolecular Transferases; C039924:2,3-oxidosqualene-beta-amyrin-cyclase; C036380:beta-amyrin; C100089:cycloartenol