Integrated metabolomic and transcriptomic analysis reveals the mechanism of high polysaccharide content in tetraploid Dendrobium catenatum Lindl

Dendrobium catenatum Lindl (Orchidaceae) has high medicinal and economic value. Unfortunately, industrially-cultivated D. catenatum exhibits inferior medicinal quality in comparison with wild-harvested plant materials. Previously, we produced tetraploid D. catenatum germplasm in order to increase the production of bioactive compounds. However, although tetraploid D. catenatum contains a higher polysaccharide content than diploid D. catenatum, the molecular mechanism is still unknown. In this study, the polysaccharide content of tetraploid D. catenatum stems and leaves was studied alongside a comprehensive transcriptomic and metabolomic analysis. Overall, tetraploid D. catenatum contained a higher polysaccharide content (stem: 30.93%, leaf: 23.28%) than diploid D. catenatum (stem: 17.93%, leaf: 15.28%). Further analyses of differential metabolites and genes were carried out, targeting genes related to polysaccharide synthesis, metabolism, regulation, and transport. Functional enrichment analysis showed that tetraploid plants were highly enriched in transport- and metabolism-related pathways. Specifically, CesA/Csl, SWEET, and BGLU gene family members were upregulated in tetraploid plants. The results of this study suggest that enhanced polysaccharide transport may be the key driver of increased polysaccharide content in tetraploid D. catenatum. These results provide a foundation for further studies aimed at resolving the molecular mechanism of high polysaccharide content in tetraploid D. catenatum, as well as a theoretical basis for the breeding of new D. catenatum varieties.