Eugenol is a natural phenolic compound known for its health-promoting properties and its ability to add a floral scent to tea plants. Plant eugenol glycosides have been identified and shown to make important contributions to fruit floral quality. However, the details of their biosynthesis and metabolism in tea plants are still unknown. Here, eugenol glucoside was unambiguously identified as a native metabolite in the tea plant, and its biosynthesis was shown to be induced by low temperature treatment. Through the analysis of UGTs induced by low temperature, the glycosyltransferase CsUGT78A15 was identified in tea, and its encoded protein was shown to catalyze the glucosylation of eugenol. V max / K m ratios showed that eugenol was the most suitable substrate for CsUGT78A15. Sugar donor preference analysis showed that CsUGT78A15 had a higher selectivity for glucose, followed by galactose and glucuronic acid. The expression of CsUGT78A15 was correlated with the accumulation of eugenol glucoside in different tissues and genotypes of tea. Down-regulation of CsUGT78A15 led to a decreased eugenol glucoside content under cold stress, indicating that CsUGT78A15 plays an important role in the biosynthesis of eugenol glucoside under cold stress. The identification of eugenol glucoside in the tea plant and the discovery of a cold stress-induced eugenol glucosyltransferase in tea provide the foundation for the improvement of tea flavor under cold stress and the biotechnological production of eugenol glucoside.
Anthocyanins are a group of natural water-soluble pigments in plants that contribute to the pink-purple color of a range of tissues. Because anthocyanins have various biological activities in human health, there is great research interest in the development of anthocyanin-rich foods and beverages, including purple shoot tea. Anthocyanidin 3- O -galactosides have been identified as one of the main anthocyanin components in purple shoot tea, but the enzyme responsible for their biosynthesis remains unclear. UDP-galactose anthocyanidin 3- O -galactosyltransferase (UA3GalT) is presumed to catalyze the galactosylation of anthocyanidin. Therefore, we assayed the UA3GalT activity in five tea samples with varying degrees of purple color and found that its activity was strongly positively correlated (r = 0.929, p < 0.05) with anthocyanin content. Phylogenetic analysis and sequence alignment suggested that CsUGT78A15 encoded a UA3GalT enzyme. Enzymatic assays indicated that r Cs UGT78A15 could catalyze the synthesis of cyanidin 3- O -galactoside and delphinidin 3- O -galactoside using UDP-galactose as a sugar donor, and it showed higher catalytic efficiency towards delphinidin than cyanidin. These results indicate that Cs UGT78A15 acts as a UA3GalT in vitro . Subcellular localization showed that Cs UGT78A15 was located in the endoplasmic reticulum (ER) and nucleus, consistent with the location of anthocyanin synthesis. Transient overexpression of CsUGT78A15 in the fruit of mature ‘Granny Smith’ apples showed that the upregulation of CsUGT78A15 promoted cyanidin 3- O -galactoside accumulation in apple skins. These results suggested that Cs UGT78A15 could catalyze galactosylation of anthocyanidins in planta . Our findings provide insight into the biosynthesis of anthocyanins in tea plants .
危险品化学品经营许可证（带存储）