Cloning and heterologous expression of cDNAs encoding flavonoid glucosyltransferases from Dianthus caryophyllus

Abstract

Yellow petals of carnations contain chalcone 2′-O-glucoside. The glucosylation occurs after the p-coumaroyl CoA and malonyl-CoA condensation reaction by chalcone synthase (CHS), but the enzyme(s) transferring glucose from UDP-glucose to the 2′-OH position of chalcone has not been identified. The full-length cDNA clones for 18 glucosyltransferase (GT) genes were isolated from petal tissue of carnation (Dianthus caryophyllus) bearing various flower colors. The 18 GTs encoded in the cDNAs were enzymatically characterized in an E. coli expression system using chalcone, flavanone, flavone, flavonol and anthocyanidin as substrates. Three of the 18 were characterized as 3-GT possessing different substrate specificities for flavonoids and anthocyanidin and another two GTs catalyzed the transfer of glucose to the 2′-hydroxyl group of chalcone. In addition, these two enzymes glucosylated flavonol (3-OH and 7-OH), flavanone (7-OH), flavone (7-OH) and anthocyanidin (3-OH and 7-OH).