The involvement of β-amyrin 28-oxidase (CYP716A52v2) in oleanane-type ginsenoside biosynthesis in Panax ginseng.

Panax species are the most popular medicinal herbs. The root of these plants contains pharmacologically active triterpene saponins, also known as ginsenosides, compounds that are divided into dammarane- and oleanane-type triterpenes. Two CYP716A subfamily genes (CYP716A47 and CYP716A53v2) were recently characterized, encoding an enzyme catalyzing the hydroxylation of dammarane-type triterpenes in Panax ginseng. Herein, we report that one CYP716A subfamily gene (CYP716A52v2) isolated from P. ginseng encodes a β-amyrin 28-oxidase, which is suggested to modify β-amyrin into oleanolic acid, a precursor of an oleanane-type saponin (mainly ginsenoside Ro) in P. ginseng. The ectopic expression of both PNY1 and CYP716A52v2 in recombinant yeast resulted in erythrodiol and oleanolic acid production, respectively. In vitro enzymatic activity assays biochemically confirmed that CYP716A52v2 catalyzed the oxidation of β-amyrin to produce oleanolic acid, and the chemical structure of the oleanolic acid product was confirmed using gas chromatography-mass spectrometry (GC/MS). Transgenic P. ginseng plants were generated via Agrobacterium tumefaciens-mediated transformation: the overexpression of CYP716A52v2 greatly increased the content of oleanane-type ginsenoside (ginsenoside Ro), whereas RNA interference against CYP716A52v2 markedly reduced it. Furthermore, the levels of other dammarene-type ginsenosides were not affected in these transgenic lines. These results indicate that CYP716A52v2 is a β-amyrin 28-oxidase that plays a key role in the biosynthesis of oleanane-type triterpenes in P. ginseng.