UDP-glycosyltransferases play a crucial role in the accumulation of alkaloids and sesquiterpene glycosides in Dendrobium nobile

Dendrobium nobile is a well-known famous traditional Chinese medicine and nourishing food in China and/or other subtropical areas. Alkaloids represented by dendrobine were considered to be the main active components in D. nobile, especially dendrobine was used as the quality marker of D. nobile in the Chinese Pharmacopoeia. Previous literature reported that the content of dendrobine in D. nobile would decrease with increasing growth years. In the present study, we analyzed the secondary metabolites in the stems of 1-year and 3-year grown D. nobile by UPLC-Q/TOF-MS. The results showed that the content of several alkaloid components, except dendrobine, decreased with the increase of growth years. Interestingly, the sesquiterpene glycosides components showed opposite accumulation patterns compared to alkaloids in D. nobile. Based on the biosynthetic pathway of dendrobine, we hypothesized that the decrease in alkaloids contents was due to the glycosylation of sesquiterpenes, the synthetic precursor compounds of alkaloids in D. nobile. The plausibility of this hypothesis was confirmed in the next transcriptome sequencing combined with RT-PCR and molecular docking. The results suggested that UDP-glycosyltransferases play a crucial role in regulating the accumulation of alkaloids and sesquiterpene glycosides in D. nobile. And it is likely that multiple UDP-glycosyltransferases act together in the glycosylation of sesquiterpenes in D. nobile. These results will provide the important information for the good agricultural practice (GAP) production of D. nobile.