Metabolic, transcriptional, and hormonal responses of Panax ginseng C. A. Meyer to nitrogen deficiency

Nitrogen (N), a key macronutrient, plays a pivotal role in modulating plant growth, development, and the synthesis of secondary metabolites. Understanding the response of medicinal plants to N deficiency is critical for optimizing their quality. However, an integrated analysis of the metabolome, transcriptome, and hormone profiles associated with N deficiency in Panax ginseng has not been previously conducted. In this study, the effects of N deprivation on Panax ginseng seedlings were investigated through comprehensive metabolic, transcriptional, and hormonal analyses. N deficiency led to an increased accumulation of nucleotides, flavonoids, phenolic acids, lipids, alkaloids, lignans, coumarins, amino acids, and their derivatives. In contrast, the content of terpenoids was significantly reduced. Additionally, alterations in the levels of auxin (IAA), cytokinin (CTK), gibberellin (GA), and jasmonic acid (JA) were observed under N deprivation. Transcriptomic analysis revealed downregulation of farnesyl diphosphate synthase (FPS) and farnesol kinase (FOLK), alongside upregulation of ten Cytochrome P450 (CYP450) genes involved in terpenoid biosynthesis. Furthermore, genes associated with IAA and CTK signaling pathways were downregulated, while genes related to GA and JA signaling were upregulated. Exogenous CTK application under N deficiency resulted in elevated levels of several terpenoid metabolites, including Oleanolic acid-3-o-Glucosyl (1→2)glucoside, 3-oxo-9,19-cyclolanost-24-en-26-Oic acid, Majoroside R1, 3-Oxoolean-12-en-28-oic Acid, Pseudoginsenoside RT5, 3-Hydroxyurs-12-en-28-oic acid, Oleanolic acid-3-o-[xylosyl(1→2)-Arabinosyl(1→6)]glucoside, and 24,30-dihydroxy-12(13)-ene-Lupeol. These results suggest that exogenous CTK can enhance the accumulation of terpenoid metabolites under N-deficient conditions in Panax ginseng. This study provides valuable insights into the molecular mechanisms underlying N regulation in Panax ginseng and offers new directions for nutrient management strategies in the ecological cultivation of this plant.