Molecular characterization of the C‐glucosylation for puerarin biosynthesis in Pueraria lobata

Summary C ‐glycosyltransferases ( CGT s) are important enzymes that are responsible for the synthesis of the C ‐glycosides of flavonoids and isoflavonoids. Flavonoid CGT s have been molecularly characterized from several plant species; however, to date, no gene encoding an isoflavonoid CGT has been reported from any plant species. A significant example of an isoflavonoid C ‐glycoside is puerarin, a compound that contributes to the major medicinal effects of Pueraria lobata . Little is known about the C ‐glucosylation that occurs during puerarin biosynthesis. One possible route for puerarin synthesis is via the C ‐glucosylation of daidzein. This study describes the molecular cloning and functional characterization of a novel glucosyltransferase (Pl UGT 43) from P. lobata . Biochemical analyses revealed that Pl UGT 43 possesses an activity for the C ‐glucosylation of daidzein to puerarin; it shows activity with the isoflavones daidzein and genistein, but displays no activity towards other potential acceptors, including flavonoids. To validate the in vivo function of Pl UGT 43 , the Pl UGT 43 gene was over‐expressed in soybean hairy roots that naturally synthesize daidzein but that do not produce puerarin. The expression of Pl UGT 43 led to the production of puerarin in the transgenic soybean hairy roots, confirming a role for Pl UGT 43 in puerarin biosynthesis.