Characterization of UDP-Glycosyltransferase SlUGT75C1 Associated with the Accumulation of Flavonol Glycosides in Tomato

Flavonol glycosides are vital for plant physiology, stress resistance, and human health. The diversity of flavonols is enriched by glycosylation modification, which is catalyzed by UDP-glycosyltransferases (UGTs). Tomato is one of the most important fruits in the world, containing high amounts of rutin and kaempferol-3-rutinoside (K3Rut). The biosynthesis of quercetin-3-glucoside (Q3Glc) and kaempferol-3-glucoside (K3Glc) constitutes a prerequisite for rutin and K3Rut formation. However, the UGTs responsible for the biosynthesis of flavonol glycosides in tomato fruit have yet to be identified. In this study, SlUGT75C1 was identified as a glucoside-specific glycosyltransferase, which catalyzes 3-<i>O</i>-glycosylation of quercetin and kaempferol. After UV-B irradiation, the content of rutin and K3Rut was decreased significantly in the <i>slugt75c1</i> mutant fruits. These results suggest that SlUGT75C1 catalyzes the biosynthesis of Q3Glc and K3Glc, which contribute to the formation of rutin and K3Rut in tomato. Our work provides an important candidate for metabolic engineering of flavonol biosynthesis in plants.