Transcriptome Analysis Reveals Molecular Mechanisms Underlying Methyl Jasmonate-mediated Biosynthesis of Protopanaxadiol-type Saponins in Panax notoginseng Leaves

Methyl jasmonate (MeJA) has been widely used to improve the biosynthesis of secondary metabolites such as triterpenoid saponins in medicinal plants. However, the underlying molecular mechanisms remain poorly understood. Differing from roots that accumulate protopanaxatriol-type saponins, Panax notoginseng leaves with a lower biomass mainly contain protopanaxadiol (PPD)-type saponins. Therefore, it is interesting to explore whether MeJA can activate the biosynthesis of PPD-type saponins in P. notoginseng leaves. In this study, we found MeJA could effectively induce the accumulation of PPD-type saponins, including ginsenoside Rb1, Rc, Rb2, Rb3 and notoginsenoside Fa, Fe in P. notoginseng leaves based on a newly established high-performance liquid chromatography method. Transcriptome analysis showed that differentially expressed genes (DEGs) induced by MeJA were mainly enriched in "terpenoid backbone biosynthesis", "biosynthesis of unsaturated fatty acids", "sesquiterpenoid and triterpenoid biosynthesis", "fatty acid metabolism", and "phenylpropanoid biosynthesis". Furthermore, the expression profile and quantitative real-time PCR analysis of DEGs showed that MeJA could positively induce the molecular response of endogenous jasmonic acid (JA) signaling pathway, and increased PPD-type saponins mediated by MeJA in P. notoginseng leaves may be related to the high expression of FPS, SS, SE, DS and UGTs, and the low expression of CYP716A53v2 and beta-AS. The results provide a molecular understanding for MeJA-elicited biosynthesis of triterpenoid saponins and facilitate the further characterization of the genes responsible for biosynthesis of PPD-type saponins in P. notoginseng leaves.