cDNA cloning and characterization of UDP-glucose: Anthocyanidin 3-O-glucosyltransferase in Iris hollandica

In anthocyanin biosynthesis, UDP-glucose: anthocyanidin 3-O-glucosyltransferase (3GT) catalyzes the transfer of the glucosyl moiety from UDP-glucose to the 3-hydroxyl group of anthocyanidins, producing the first stable anthocyanins. A cDNA clone (Ih3GT) encoding 3GT was isolated from a cDNA library of flower buds from Iris hollandica by screening with a 3GT cDNA clone of Antirrhinum majus. The cDNA encodes an open reading frame of 460 amino acids with a calculated molecular mass of 49,558 Da and an isoelectric point of 5.54. The molecular mass of recombinant Ih3GT protein from Escherichia coli was also estimated to be ca. 50 kDa by Western blotting. A molecular phylogenetic analysis of the deduced amino acid sequences of glycosyltransferases from various plants showed that Ih3GT is a member of 3GT group, which is further classified into monocot and dicot subgroups. Characterization of the enzymatic properties using the recombinant Ih3GT protein showed that Ih3GT cDNA encodes anthocyanidin 3-O-glucosyltransferase. This is the first report of 3GT gene cloning from an ornamental monocot plant.