Involvement of Three CsRHM Genes from Camellia sinensis in UDP–Rhamnose Biosynthesis

UDP–Rhamnose synthase (RHM), the branch-point enzyme controlling the nucleotide sugar interconversion pathway, converts UDP–d-glucose into UDP–rhamnose. As a rhamnose residue donor, UDP–l-rhamnose is essential for the biosynthesis of pectic polysaccharides and secondary metabolites in plants. In this study, three CsRHM genes from tea plants (Camellia sinensis) were cloned and characterized. Enzyme assays showed that three recombinant proteins displayed RHM activity and were involved in the biosynthesis of UDP–rhamnose in vitro. The transcript profiles, metabolite profiles, and mucilage location suggest that the three CsRHM genes likely contribute to UDP–rhamnose biosynthesis and may be involved in primary wall formation in C. sinensis. These analyses of CsRHM genes and metabolite profiles provide a comprehensive understanding of secondary metabolite biosynthesis and regulation in tea plants. Moreover, our results can be applied for the synthesis of the secondary metabolite rhamnoside in future studies.