The Rhododendron agastum flavonoid 3-O-glycosyltransferase Ra3GT2 contributes to salt and drought stress tolerance through modulating anthocyanin synthesis

Abstract

Flavonoid 3-O-glycosyltransferases (3GTs), in charge of transferring UDP-sugars to 3-OH position of small substrates, control a variety of metabolic processes in plants. Extensive research about 3GTs has been centered in model plants, but little in Rhododendron. Here, three 3GT genes (Ra3GT1-3) were isolated from R. agastum flowers. Based on analyses of sequence alignment and phylogenetic tree, only Ra3GT2 had the full-length ORF and was grouped into the set of flavonoid 3-O-glycosyltransferase, so it was selected for further characterization. Ra3GT2 expression during R. agastum flower development did not align with anthocyanin accumulation, suggesting it may glycosylate both anthocyanidins and other flavonoids. The function of Ra3GT2 in vivo was identified in ugt78d2 mutant as well as K326 tobacco, and the data revealed that Ra3GT2 transgenes could restore the purple color of the ugt78d2 seedlings and deepen the flower color of tobacco via regulating the expressions of endogenous genes participated in anthocyanin synthesis. Furthermore, Ra3GT2 was confirmed to modify flavonoids through adding UDP-glucose and UDP-galactose to the 3-OH of anthocyanidins and flavonols. Ra3GT2 overexpression enhanced salt and drought tolerance in both Arabidopsis and E. coli, whereas the ugt78d2 mutant and control strains were more stress-sensitive. Taken together, we demonstrate that Ra3GT2 plays important roles in modulating anthocyanin biosynthesis as well as enviromental stress tolerance.