Constitutive activation of genes involved in triterpene saponins enhances the accumulation of saponins in three-year-old Panax notoginseng growing under moderate light intensity

Abstract

Light is an important physical factor that regulates plant developmental patterns and induces the synthesis of secondary metabolites. The optimal light intensity for saponin accumulation in roots of medicinal plants with different ages is relatively poorly understood. After that, the correlation of light-driven biosynthesis of triterpene saponins with the expression of genes incorporated into the biosynthesis of triterpene saponins is still unknown. The expression levels of genes, the total saponin contents, and the biomass accumulation and allocation were examined in different age Panax notoginseng grown under different light intensities. A significant elevation in total saponin content was found in three-year-old plants grown under 9.6 % of full sunlight (FL) condition compared with the others. The expression level of dammarenediol-II synthase (DS) rapidly increased from one-year-old plants to three-year-old plants, which was consistent with the change in total saponins. Furthermore, there is a positive relationship between the expression level of DS and the content of saponins. Additionally, 9.6 % FL-driven biosynthesis of saponin has more activity in the three-year-old P. notoginseng, and the genes expression level of CYP716A47 was elevated. At the same time, the expression of geranylgeranyl pyrophosphate synthase (GGPS) and phosphomevalonate kinase (PMK) had no positive contribution to the accumulation of saponins in roots. Overall, DS and CYP716A47 might attribute to the accumulation of saponins in three-year-old P. notoginseng under a moderate light regime (about 10 % FL).