Cloning and Characterization of the Gene Encoding HMGS Synthase in Polygonatum sibiricum

The saponins of Polygonatum sibiricum had many pharmacological activities such as antitumor, antioxidation, and blood sugar lowering, which were synthesized by two pathways: mevalonate (MVA) and methylerythritol phosphate (MEP). 3-Hydroxy-3-methylglutaryl coenzyme A synthase (HMGS) was the key enzyme in the MVA synthesis pathway, and its expression level may affect the accumulation of saponins which were the main active ingredients of P. sibiricum. In this study, we successfully cloned HMGS1 and HMGS2 from P. sibiricum and their sequence similarity was 93.71% with 89 different sites. The multiple sequence alignment results indicated that the N-terminal sequences of HMGS were conserved. Phylogenetic analysis showed that P. sibiricum, A. officinalis, N. tazetta, D. nobile, and other relatives had a common evolutionary ancestor. The expression levels of both HMGSs and the total saponin content in different tissues revealed that HMGS expression in rhizomes was positively correlated with total saponin content. Further study of the abiotic stress effect of Methyl Jasmonate (MeJA) demonstrated that the expression of HMGS1 and HMGS2 genes was induced by MeJA, peaked at 24 h, and fell by 48 h. Our present findings would provide a blueprint for future studies of HMGS and its role in triterpenoid biosynthesis in P. sibiricum.