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A genomics approach to the early stages of triterpene saponin biosynthesis in Medicago truncatula
Author(s) -
Suzuki Hideyuki,
Achnine Lahoucine,
Xu Ran,
Matsuda Seiichi P. T.,
Dixon Richard A.
Publication year - 2002
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.2002.01497.x
Subject(s) - triterpene , squalene monooxygenase , medicago truncatula , hederagenin , methyl jasmonate , biochemistry , sapogenin , sterol , biology , saponin , phenylpropanoid , medicago , chemistry , biosynthesis , enzyme , gene , genetics , medicine , alternative medicine , symbiosis , pathology , cholesterol , bacteria
Summary 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 β‐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 β‐amyrin synthase (β‐AS). SS was functionally characterized by expression in Escherichia coli , two forms of SE by complementation of the yeast erg1 mutant, and β‐AS by expression in yeast. β‐Amyrin was the sole product of the cyclization of squalene epoxide by the recombinant M. truncatula β‐AS, as judged by GC–MS and NMR. Transcripts encoding β‐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.