ABSTRACT
Rutin, a 3-rutinosyl quercetin, is a representative flavonoid distributed in many plant species, and is highlighted for its therapeutic potential. In this study, we purified uridine diphosphate-rhamnose: quercetin 3-O-glucoside 6â³-O-rhamnosyltransferase and isolated the corresponding cDNA (FeF3G6â³RhaT) from seedlings of common buckwheat (Fagopyrum esculentum). The recombinant FeF3G6â³RhaT enzyme expressed in Escherichia coli exhibited 6â³-O-rhamnosylation activity against flavonol 3-O-glucoside and flavonol 3-O-galactoside as substrates, but showed only faint activity against flavonoid 7-O-glucosides. Tobacco cells expressing FeF3G6â³RhaT converted the administered quercetin into rutin, suggesting that FeF3G6â³RhaT can function as a rhamnosyltransferase in planta. Quantitative PCR analysis on several organs of common buckwheat revealed that accumulation of FeF3G6â³RhaT began during the early developmental stages of rutin-accumulating organs, such as flowers, leaves, and cotyledons. These results suggest that FeF3G6â³RhaT is involved in rutin biosynthesis in common buckwheat.
