A genomics approach to the early stages of triterpene saponin biosynthesis in Medicago truncatula

• DOI: 10.1046/j.1365-313x.2002.01497.x
• Publication Date: 2003-03-12T22:08:24Z
• Authors: Hideyuki Suzuki; Lahoucine Achnine; Ran Xu; Seiichi P. T. Mat...; Richard A. Dixon
• Keywords: Squalene monooxygenase; Medicago truncatula; Hederagenin; Methyl jasmonate; Sapogenin; Phenylpropanoid; Medicago

Summary The saponins of the model legume Medicago truncatula are glycosides at least five different triterpene aglycones: soyasapogenol B, E, medicagenic acid, hederagenin and bayogenin. These aglycones most likely derived from β‐amyrin, a product cyclization 2,3‐oxidosqualene. Mining M. EST data sets led to identification sequences putatively encoding three early enzymes aglycone formation: squalene synthase (SS), epoxidase (SE), β‐amyrin (β‐AS). SS was functionally characterized by expression in Escherichia coli , two forms SE complementation yeast erg1 mutant, β‐AS yeast. β‐Amyrin sole epoxide recombinant β‐AS, as judged GC–MS NMR. Transcripts one form were strongly co‐ordinately induced, associated with accumulation triterpenes, upon exposure cell suspension cultures methyl jasmonate. Sterol composition remained unaffected jasmonate treatment. Molecular verification induction pathway culture system provides new tool for saponin gene discovery DNA array‐based approaches.