UDP-dependent glycosyltransferases (UGTs) convert aglycones into more stable, bioactive, and structurally diverse glycosylated derivatives. Pomegranate (Punica granatum L.) produces various glycosylated phenolic metabolites, e.g. hydrolyzable tannins (HTs), anthocyanins, and flavonoids, and constitutes an excellent system for investigating the corresponding UGT activities. Here we report the cloning and functional characterization of a pomegranate UGT, PgUGT95B2, which is highly active towards flavones and flavonols and can glycosylate at more than one position in the substrate molecule. Particularly, PgUGT95B2 has the strongest activity towards tricetin (flavone with a tri-hydroxylated B-ring) and can act at the 4'-O position of its B-ring. In addition, PgUGT95B2 was able to glycosylate flavones present in pomegranate metabolite extracts. Conversely, PgUGT95B2 did not produce a galloylglucose ester (precursor for HT biosynthesis) or anthocyanins in enzyme assays. Our phylogenetic analysis suggested an independent evolution of PgUGT95B2 and flavone/flavonol UGTs identified in the model plant Arabidopsis thaliana through convergent evolution or gene loss.

中文翻译：

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PgUGT95B2 优先代谢黄酮/黄酮醇，并独立于拟南芥中鉴定的黄酮/黄酮醇 UGT 进化

UDP 依赖性糖基转移酶 (UGT) 将苷元转化为更稳定、生物活性和结构多样化的糖基化衍生物。石榴 (Punica granatum L.) 会产生各种糖基化酚类代谢物，例如可水解单宁 (HT)、花青素和类黄酮，是研究相应 UGT 活性的绝佳系统。在这里，我们报告了石榴 UGT PgUGT95B2 的克隆和功能表征，它对黄酮和黄酮醇具有高度活性，并且可以在底物分子中的多个位置进行糖基化。特别是，PgUGT95B2 对 Tricetin（具有三羟基化 B 环的黄酮）的活性最强，并且可以作用于其 B 环的 4'-O 位置。此外，PgUGT95B2 能够使石榴代谢产物提取物中存在的黄酮糖基化。相反，PgUGT95B2 在酶分析中不产生没食子酰葡萄糖酯（HT 生物合成的前体）或花青素。我们的系统发育分析表明 PgUGT95B2 和黄酮/黄酮醇 UGT 在模式植物拟南芥中通过趋同进化或基因丢失独立进化。