Engineering of Triterpene Biosynthesis to Develop a Production System for Useful Compounds

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cDNA cloning of triterpene synthases was carried out from triterpene producing plants. As a result, a new clone was cloned from a root of dandelion (Taraxacum officinale) which was identified to be achilleol synthase by its expression in yeast. Amino acid sequence of achilleol synthase has a high homology to those of beta-amyrin synthases, and this clone has joined to the branch of beta-amyrin synthases in phylogenetic analysis. It is very interesting that this clongives a mono-cyclic products instead of penta-cyclic product such as beta-amyrin. This clone has a glycine residue at the position of two amino acid upstream from DCTAE motif which is found in all oxidosqualene cyclase although all of beta-amyrin synthasq as valine residue at this position. When this glycine residue in achilleol synthase was changed to valine residue by site-direct mutagenesis, product was changed to beta-amyrin, suggesting that achilleol synthase was evolved from beta-amyrin synthase. The approach of this study is considered to be a new approach for isolation of a new compound by functional genomics since achilleol had not been isolated from dandelion itself although it was isolated from the other composite plant.cDNA cloning of triterpene hydroxylase as also carried out from soybean (Glycine max) which produced soyasaponins. More than two hundreds kinds of P450 EST clone from soybean were registered in data base. Among them, the clones (6 clones) which cover full-length region and function was not identified were cloned from soybean seedlings and expressed in yeast. CYP93E1, one of tested clones, showed 24-hydroxylation activity against beta-amyrin.