Catalytic specificity of pea O-methyltransferases suggests gene duplication for (+)-pisatin biosynthesis

Two highly homologous isozymes of (+)-6a-hydroxymaackiain 3-O-methyltransferase (HMM) have been identified in pea. Catalytic activity studies suggest HMM1 functions early in isoflavonoid biosynthetic pathway to produce the common intermediate formononetin while HMM2 functions specifically in the biosynthesis of the phytoalexin (+)-pisatin. We propose that HMM2 evolved by gene duplication.