AUTHOR=Su Xiaojia , Shen Guoan , Di Shaokang , Dixon Richard A. , Pang Yongzhen 

TITLE=Characterization of UGT716A1 as a Multi-substrate UDP:Flavonoid Glucosyltransferase Gene in Ginkgo biloba

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.02085

DOI=10.3389/fpls.2017.02085

ISSN=1664-462X

ABSTRACT=<p><italic>Ginkgo biloba</italic> L., a “living fossil” and medicinal plant, is a well-known rich source of bioactive flavonoids. The molecular mechanism underlying the biosynthesis of flavonoid glucosides, the predominant flavonoids in <italic>G. biloba</italic>, remains unclear. To better understand flavonoid glucosylation in <italic>G. biloba</italic>, we generated a transcriptomic dataset of <italic>G. biloba</italic> leaf tissue by high-throughput RNA sequencing. We identified 25 putative UDP-glycosyltransferase (<italic>UGT</italic>) unigenes that are potentially involved in the flavonoid glycosylation. Among them, we successfully isolated and expressed eight <italic>UGT</italic> genes in <italic>Escherichia coli</italic>, and found that recombinant UGT716A1 protein was active toward broad range of flavonoid/phenylpropanoid substrates. In particular, we discovered the first recombinant UGT protein, UGT716A1 from <italic>G. biloba</italic>, possessing unique activity toward flavanol gallates that have been extensively documented to have significant bioactivity relating to human health. <italic>UGT716A1</italic> expression level paralleled the flavonoid distribution pattern in <italic>G. biloba</italic>. Ectopic over-expression of <italic>UGT716A1</italic> in <italic>Arabidopsis thaliana</italic> led to increased accumulation of several flavonol glucosides. Identification and comparison of the <italic>in vitro</italic> enzymatic activity of UGT716A1 homologs revealed a UGT from the primitive land species <italic>Physcomitrella patens</italic> also showed broader substrate spectrum than those from higher plants <italic>A. thaliana, Vitis vinifera</italic>, and <italic>Medicago truncatula</italic>. The characterization of <italic>UGT716A1</italic> from <italic>G. biloba</italic> bridges a gap in the evolutionary history of <italic>UGTs</italic> in gymnosperms. We also discuss the implication of <italic>UGT716A1</italic> for biosynthesis, evolution, and bioengineering of diverse glucosylated flavonoids.</p>