Cold Stress-induced Glucosyltransferase CsUGT78A15 is Involved in the Formation of Eugenol Glucoside in Camellia sinensis

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. Vmax/Km 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.