Genome-wide characterization of glycosyltransferases involved in C-glycosylation and the metabolism of small molecules in the tea plant (Camellia sinensis)

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Leaves and leaf buds of the tea plant (Camellia sinensis) used to make tea are a rich source of bioactive phytochemicals that frequently occur as O- and C-glycoconjugates. C-glycosides show biological activity similar to the respective O-glycoside, but display at the same time a substantially improved stability against in vivo clearance, which make them attractive for medicinal chemistry. Uridine diphosphate-sugar (UDP)-dependent glycosyltransferases (UGTs) usually mediate glycosylation of plant metabolites by catalysing the transfer of an activated nucleotide sugar donor to a range of acceptor aglycones to form glycosides. Although glycoside precursors determine tea plant performance as well as the quality of the product tea, the genes and enzymes involved in the glycosylation of small molecules, especially the C- glycosylation in the tea plant, are rarely studied. Only recently, the Chinese partners have published the genome sequence of C. sinensis var. sinensis, which provided insights into the evolution of the tea genome and tea quality. Since the German and Chinese partners have extensive experience in the biotechnological production of small molecule glucosides and the characterization of plant UGTs, respectively, as demonstrated by several joint publications, it is now possible to characterize the genes and enzymes involved in the biosynthesis of low-molecular glycosides in tea plants and to facilitate their biotechnological production. We identified 298 UGT family 1 genes in the tea genome database. In the current project, the Chinese and German groups would like to investigate the genome expansion mechanisms by bioinformatics analysis and isolate all UGT family 1 genes from the tea plant. It is planned to express the recombinant proteins in host organisms, identify potential donor and acceptor substrates by high-throughput screens and investigate the biological function of selected candidates by overexpression and downregulation in transgenic plant systems. The activity of the UGTs will be analysed by both in vitro assays and biotransformation experiments. Functional characterization of candidates will be performed in planta in Arabidopsis thaliana, Nicotiana benthamiana and Camellia sinensis as well as by comparative transcriptome and metabolite profiling analyses. The focus will be on UGTs involved in the C-glycosylation, the metabolism of aroma chemicals and plant defence. These results will provide the foundation for improvement of tea flavour and tea plant defence, as well as the biotechnological production of bioactive C-glycosides with improved stability against hydrolysis.