Molecular cloning and biochemical characterization of a new flavonoid glycosyltransferase from the aquatic plant lotus.

Lotus (Nelumbo nucifera Gaertn.), one of the earliest plants in angiosperms, is a perennial aquatic herb widely distributed throughout Eastern Asia. Quercetin and its glycosides are the most abundant phenolic compounds in lotus with multiple pharmacological activities. Although many flavonoid O-glycosyltransferases involved in the biosynthesis of quercetin glycosides have been identified from terrestrial plants, no glycosyltransferase has been identified in aquatic plants. In this study, a new glycosyltransferase (NpUGT6) was identified from the embryo of Nelumbo nucifera (Nelumbinis Plumula). Function characterization demonstrated that NpUGT6 exhibited a robust capability to regio- and stereo-specific O-glycosylation at the 3-hydroxy group of quercetin scaffolds with UDP-glucose. Moreover, the O-glycosylation catalyzed by NpUGT6 was reversible. NpUGT6 is the first identified flavonoid O-glycosyltransferase from aquatic plants. Its sequence will provide useful guidance for the discovery of additional flavonoid glycosyltransferses in Nymphaeaceae and other aquatic plants.