cDNA cloning of a BAHD acyltransferase from soybean (Glycine max): isoflavone 7-O-glucoside-6''-O-malonyltransferase.

A cDNA from soybean (Glycine max (L.) Merr.), GmIF7MaT, encoding malonyl-CoA:isoflavone 7-O-glucoside-6''-O-malonyltransferase, was cloned and characterized. Soybeans produce large amounts of isoflavones, which primarily accumulate in the form of their 7-O-(6''-O-malonyl-beta-D-glucosides). The cDNA was obtained by a homology-based strategy for the cDNA cloning of some flavonoid glucoside-specific malonyltransferases of the BAHD family. The expressed gene product, GmIF7MaT, efficiently catalyzed specific malonyl transfer reactions from malonyl-CoA to isoflavone 7-O-beta-D-glucosides yielding the corresponding isoflavone 7-O-(6''-O-malonyl-beta-D-glucosides) (IF7MaT activity). The k(cat) values of GmIF7MaT were much greater than those of other flavonoid glucoside-specific malonyltransferases with their preferred substrates, while the K(m) values were at comparable levels. GmIF7MaT was expressed in the roots of G. max seedlings more abundantly than in hypocotyl and cotyledon. Native IF7MaT activity was also observed in the roots, suggesting that GmIF7MaT is involved in the biosynthesis from isoflavone 7-O-beta-D-glucosides to the corresponding isoflavone 7-O-(6''-O-malonyl-beta-D-glucosides) in G. max. This protein is a member of flavonoid glucoside-specific acyltransferases in the BAHD family.