[Cloning and function characterization of a UDP-rhamnose synthase from Dendrobium huoshanense]

UDP-rhamnose, which is synthesized under the catalysis by the rhamnose synthase(RHM), is an essential sugar donor for the synthesis of rhamnoside in plants. Based on the reported rhamnose synthase, this study screened one RHM gene(DhuRHM) from the localized gene database of Dendrobium huoshanense by sequence alignment. This gene was cloned, and then bioinformatics analysis and in vitro functional verification were carried out. The results revealed that DhuRHM had an open reading frame of 2 016 bp, encoding a protein with 671 residues, a molecular weight of 75.43 kDa, and a theoretical isoelectric point of 6.12. Subcellular localization analysis indicated that DhuRHM was located on the cell membrane. Multiple sequence alignments and the phylogenetic tree showed that DhuRHM possessed the characteristic domains(GxxGxxG/A and YxxxK) of the plant RHM family and presented high homology with the RHMs of other species. DhuRHM had the activity to catalyze the transformation of UDP-glucose into UDP-rhamnose. Furthermore, RT-qPCR results showcased that the expression level of DhuRHM in stems was higher than those in leaves and roots. Among four abiotic stress conditions(high temperature, low temperature, drought, and ultraviolet radiation) and MeJA treatment, ultraviolet radiation, low temperature, and high temperature significantly up-regulated the expression of DhuRHM. This study is the first to obtain a rhamnose synthase from D. huoshanense and identify its functions. The findings enrich the knowledge about the plant RHM family and provide a reference for the research on the UDP-rhamnose biosynthetic pathway in D. huoshanense and the responses of related metabolites to environmental stress.