Identification and Characterization of Two Regiospecific Tricetin UDP-Dependent Glycosyltransferases from Pomegranate (Punica granatum 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'-O-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'-O-glucoside accumulate in anthers, but not petals. In addition, the comparative analysis of anther and petal transcriptomes identified 10 UGTs that are more highly expressed in anthers than petals. Of the 10 UGTs, PgUGT76Z1 and PgUGT73AL1 glucosylated specifically at the 4'-O position of tricetin to form tricetin 4'-O-glucoside. The phylogenetic analysis indicated that PgUGT76Z1 and PgUGT73AL1 belong to different plant UGT groups, suggesting a convergent evolution of these tricetin UGTs. Overall, identification and characterization of PgUGT76Z1 and PgUGT73AL1 not only provides evolutionary insights into tricetin glucosylation, but also offers an opportunity to produce tricetin 4'-O-glucoside in large quantities through microbial biotransformation or plant metabolic engineering, thus facilitating the investigation of tricetin 4'-O-glucoside bioactivities.

Automated summary

This study revealed the accumulation of tricetin and tricetin 4'-O-glucoside in pomegranate floral tissues, specifically in anthers. Comparative transcriptome analysis identified 10 UGTs that are responsible for the glucosylation of tricetin, with PgUGT76Z1 and PgUGT73AL1 specifically glucosylating tricetin at the 4'-O position. Phylogenetic analysis suggested a convergent evolution of these tricetin UGTs. The identification and characterization of PgUGT76Z1 and PgUGT73AL1 provide insights into tricetin glucosylation and offer the potential for large-scale production of tricetin 4'-O-glucoside for further study of its bioactivities.