AUTHOR=Meng Xiangyu , Li Yueqing , Zhou Tongtong , Sun Wei , Shan Xiaotong , Gao Xiang , Wang Li 

TITLE=Functional Differentiation of Duplicated Flavonoid 3-O-Glycosyltransferases in the Flavonol and Anthocyanin Biosynthesis of Freesia hybrida

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.01330

DOI=10.3389/fpls.2019.01330

ISSN=1664-462X

ABSTRACT=<p>Flavonols and anthocyanins are two widely distributed groups of flavonoids that occurred apart during plant evolution and biosynthesized by shared specific enzymes involved in flavonoid metabolism. UDP-glucose, flavonoid 3-<italic>O</italic>-glycosyltransferase (UF3GT), is one of the common enzymes which could catalyze the glycosylation of both flavonol and anthocyanidin aglycons simultaneously <italic>in vitro</italic>. However, whether and how <italic>UF3GT</italic> paralogous genes function diversely at the biochemical and transcriptional levels are largely unknown. Recently, <italic>Fh3GT1</italic> was identified to be a member of <italic>UF3GT</italic>s in <italic>Freesia hybrida</italic>. However, its expression patterns and enzymatic characteristics could not coincide well with flavonol accumulation. In an attempt to characterize other flavonoids, especially flavonol glycosyltransferase genes in <italic>Freesia</italic>, three closest candidate <italic>UFGT</italic> genes—<italic>Fh3GT2</italic>, <italic>Fh3GT3</italic>, and <italic>Fh3GT4</italic>—were mined from the <italic>Freesia</italic> transcriptomic database and isolated from the flowers of the widely distributed <italic>Freesia</italic> cultivar, Red River<sup>®</sup>. Based on bioinformatic analysis and enzymatic assays, <italic>Fh3GT2</italic> turned out to be another <italic>bona fide</italic> glycosyltransferase gene. Biochemical analysis further proved that Fh3GT2 preferentially glucosylated kaempferol while <italic>Fh3GT1</italic> controlled the glucosylation of quercetin and anthocyanidins. In addition, transfection assays demonstrated that <italic>Fh3GT2</italic> could be mainly activated by the flavonol regulator FhMYBF1 or the anthocyanin regulator FhPAP1, whereas <italic>Fh3GT1</italic> could only be activated by FhPAP1. These findings suggested that <italic>Fh3GT</italic>s might have functionally diverged in flavonoid biosynthesis at both the biochemical and transcriptional levels.</p>