Molecular Characterization of the Enzyme Catalyzing the Aryl Migration Reaction of Isoflavonoid Biosynthesis in Soybean

The first specific reaction in the biosynthesis of isoflavonoid compounds in plants is the 2-hydroxylation, coupled to aryl migration, of a flavanone. Using a functional genomics approach, we have characterized a cDNA encoding a 2-hydroxyisoflavanone synthase from soybean (Glycine max). Microsomes isolated from insect cells expressing this cytochrome P450 from a baculovirus vector convert 4′,7-dihydroxyflavanone (liquiritigenin) to 4′,7-dihydroxyisoflavone (daidzein), most likely via 2,4′,7-trihydroxyisoflavanone which spontaneously dehydrates to daidzein. The enzyme also converts naringenin (4′,5,7-trihydroxyflavanone) to genistein, but at a lower rate. 2-Hydroxyisoflavanone synthase transcripts are strongly induced in alfalfa cell suspensions in response to elicitation.