Two phylogenetic classes of UDP-sugar:glycosyltransferase responsible for 7-O-glucuronosylation and 7-O-glucosylation of flavonoids in Lamiales

Abstract

Flavonoid, a huge class of plant secondary metabolites, is generally modified with various sugar moieties. Glycosylation is catalyzed by UDP-glycosyltransferase (UGT), and considered to play important roles not only to increase stability and solubility of flavonoids but also provide hydroxyl residues for further modifications. It is accepted that phylogenetics and biochemical functions (i.e., glycosyl-acceptor specificity and regiospecificity) of flavonoid UGTs are correlated. Here we report the identification and characterization of four flavonoid 7-O-glucuronosyltransferases (F7GAT) and three flavonoid 7-O-glucosyltransferases (F7GlcT) from Lamiales order. The 7GATs specifically utilized UDP-glucuronic acid as their UDP-sugar donor, whereas 7GlcTs utilize UDP-glucose but not UDP-glucuronic acid. The 7GATs form a phylogenetic subclade, apparently apart from the cluster III represented by flavonoid 7GlcTs. This structural diversity suggests that the functional differentiation of UGTs had occurred locally in plant evolution.