UGT707B2 From Iris tectorum Maxim.: A Promiscuous Glycosyltransferase for the Biosynthesis of Structurally Diverse Flavonoid Glycosides

Iris tectorum Maxim. (I. tectorum) is a medicinal plant in China, known for its efficacy in treating upper respiratory diseases. It contains an abundance of (iso)flavonoid glycosides, which exhibit extensive pharmacological activities. Due to their broad prospects for pharmaceutical applications, (iso)flavonoid glycosides have attracted increasing attention. In the biosynthetic pathway of (iso)flavonoid glycosides, glycosyltransferases are key downstream enzymes that catalyze their formation. However, the glycosyltransferases involved in the biosynthesis pathway of (iso)flavonoid glycosides from I. tectorum remain largely unidentified. In this study, a candidate glycosyltransferase gene, UGT707B2, was identified and screened out from the transcriptome data of I. tectorum. Phylogenetic analysis showed that UGT707B2 clustered clearly with the (iso)flavone UGTs. An in vitro enzymatic reaction assay showed that UGT707B2 could catalyze the 7-OH glycosylation of the isoflavone substrate tectorigenin, producing tectoridin. UGT707B2 also showed glycosylation activities toward various flavonoids, including dihydrochalcone, flavonoids, and flavonols. In particular, UGT707B2 converted phloretin into the corresponding glycoside at nearly 100% conversion. Collectively, this study not only broadens the known repertoire of plant (iso)flavonoid glycosyltransferases but also offers a promising biocatalyst for the synthesis of high-value, structurally diverse (iso)flavonoid glycosides.