Metabolomic and transcriptomic analysis of Panax Notoginseng root: Mechanistic insights into the effects of flower bud removal on yield and phytochemical composition

Abstract

The roots of Panax notoginseng (Burk.) F. H. Chen are used to treat organ damage and cardiovascular diseases in several East Asian countries. The removal of floral buds before inflorescence formation is widely employed to increase rhizome yield in the cultivation of Panax notoginseng. However, the molecular mechanisms regulating the growth and the accumulation of secondary metabolites remain unclear. We find that after the removal of flower buds, the root biomass accumulated in three-year-old Panax notoginseng after growing for four months increased by 27 %. Comparative transcriptomic and metabolomic analyses revealed that disbudding promoted the conversion of small molecule sugars to polysaccharides by regulating the expression of genes in the glycogen metabolism (GLG) family. It facilitated the accumulation of metabolites in the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway by upregulating the expression of isoprenoid synthase (ISP) family genes and inhibited the conversion from the tricarboxylic acid (TCA) cycle to the mevalonate (MVA) pathway by downregulating the expression of acetyl-CoA acetyltransferase (ACAT) family genes. At the same time, the total content of triterpene saponins, main active ingredients, basically remained unchanged. However, the content of intermediate saponins increased after the upregulation of cytochrome P450 monooxygenase (CYP) transcripts, while that of downstream saponins decreased after the downregulation of UDP-glucuronosyltransferase (UGT) transcripts. Additionally, scanning electron microscopy (SEM) observations of root cross-sections indicated that the disbudding potentially promoted the development of the primary root cortex and epidermis by regulating auxin-cytokinin (AUX-CTK) signaling, thus alleviating xylem cavitation. This study confirms the removal of flower buds as an effective way to enhance yield of Panax notoginseng, offering new insights into the basic mechanisms of growth regulation during plant reproductive development and providing valuable reference for studying metabolite accumulation patterns in Panax notoginseng and other medicinal plants in the Panax genus.