Identification of a Flavonoid Glucosyltransferase Involved in 7-OH Site Glycosylation in Tea plants

• 1、State Key Laboratory of Tea Plant Biology and Utilization, Anhui Agricultural University, Hefei, Anhui 230036, China
• 2、School of Life Science, Anhui Agricultural University, Hefei, Anhui 230036, China

Abstract：Flavonol glycosides, which are often converted from aglycones catalyzed by UDP-glycosyltransferases (UGTs), play important roles for the health of plants and animals. In present study, CsUGT75L12, a gene encoding a flavonoid 7-O-glycosyltransferase, was identified in tea plants. Recombinant CsUGT75L12 protein displayed glycosyltransferase activity with multiple phenolic compounds including flavanone, flavone, flavonol and isoflavone on the 7-OH position. In relative comparison to wild-type seeds, the content of flavonol-glucosides levels increased in seeds of Arabidopsis overexpressing CsUGT75L12. In order to determine the key amino acid residues responsible for the catalytic activity of the protein, a series of site-directed mutagenesises and enzymatic assays were performed based on the 3D structural modeling and docking analysis. These results suggested that residue Q54 was predicted to be a double binding site functioning as a sugar receptor and donor. Residues H56 and T151 corresponding to the basic active residues H20 and D119 of VvGT1, were not irreplaceable for CsUGT75L12. In addition, residues Y182, S223, P238, T239, and F240 were demonstrated to be responsible for a "reversed" sugar receptor binding model. The results of triple substitution confirmed that the function of residues P238, T239 and F240 may substitute or compensate with each other for the flavonoid 7-O-glycosyltransferase active.?????

keywords： Camellia sinensis, phenolic compounds, Flavonoid 7-O-glucosyltransferase, Homology modeling, Site-directed mutagenesis, and truncation experiment

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