Identification and Characterization of Two Regiospecific Tricetin UDP-Dependent Glycosyltransferases from Pomegranate ( L.).

Tricetin (5,7,3',4',5'-pentahydroxyflavone) is a dietary flavone from flowers of Myrtales plants with demonstrated functions in promoting human health. By contrast, the bioactivity of its glucosylated derivative tricetin 4'--glucoside has not been extensively explored. We conducted metabolite profiling analysis of pomegranate (a Myrtales plant) floral tissues and revealed that tricetin and tricetin 4'--glucoside accumulate in anthers, but not petals. In addition, the comparative analysis of anther and petal transcriptomes identified 10 that are more highly expressed in anthers than petals. Of the 10 UGTs, UGT76Z1 and UGT73AL1 glucosylated specifically at the 4'- position of tricetin to form tricetin 4'--glucoside. The phylogenetic analysis indicated that UGT76Z1 and UGT73AL1 belong to different plant UGT groups, suggesting a convergent evolution of these tricetin UGTs. Overall, identification and characterization of UGT76Z1 and UGT73AL1 not only provides evolutionary insights into tricetin glucosylation, but also offers an opportunity to produce tricetin 4'--glucoside in large quantities through microbial biotransformation or plant metabolic engineering, thus facilitating the investigation of tricetin 4'--glucoside bioactivities.