Molecular cloning and characterization of an isoflavone 7-O-glucosyltransferase from Pueraria lobata

Jia Li, Zhaobo Li, Changfu Li, Junbo Gou, Yansheng Zhang

A novel isoflavone 7- O -glucosyltransferase PlUGT1 was isolated from Pueraria lobata . PlUGT1 could convert daidzein to daidzin, genistein to genistin as well as formononetin to ononin. Pueraria lobata roots are traditionally consumed as a rich source of isoflavone glycosides that have various human health benefits. However, to date, the genes encoding isoflavone UDP-glycosyltransferases (UGTs) have only been isolated from the roots of soybean seedlings (GmIF7GT), soybean seeds (UGT73F2) and Glycyrrhiza echinata cell suspension cultures (GeIF7GT). To investigate the isoflavone metabolism in P. lobata, 40 types of partial UGT cDNAs were isolated from P. lobata, and seven full-length UGT candidates with preferential expression in roots were identified. Functional assays in yeast (Saccharomyces cerevisiae) revealed that one of these UGT candidates, designated PlUGT1 (official UGT designation UGT88E12), efficiently glycosylated isoflavone aglycones at the 7-hydroxy group. Recombinant PlUGT1 purified from Escherichia coli cells was characterized and shown to be relatively specific for isoflavone aglycones, while flavonoid substrates were poorly accepted. The biochemical results suggested that PlUGT1 was an isoflavone 7-O-glucosyltransferase. The deduced amino acid sequence of PlUGT1 shared only 26 % identity with GeIF7GT, 27 % with UGT73F2 and 63 % with GmIF7GT. The PlUGT1 gene was highly expressed in P. lobata roots relative to other organs and strongly induced by methyl jasmonate signal in P. lobata cell suspension culture. The transcript abundance of PlUGT1 was correlated with the accumulation pattern of isoflavone glycosides such as daidzin in P. lobata plants or in cell suspension culture. The biochemical properties and gene expression profile supported the idea that PlUGT1 could play a role in isoflavone glycosylation in P. lobata.