College of Agronomy & Biotechnology, Yunnan Agricultural University, Kunming, 650201, China; Key Laboratory of Medicinal Plant Biology of Yunnan Province, Yunnan Agricultural University, Kunming, 650201, China; National & Local Joint Engineering Research Center on Germplasm Innovation & Utilization of Chinese Medicinal Materials in Southwestern China, Yunnan Agricultural University, Kunming, 650201, China.
College of Agronomy & Biotechnology, Yunnan Agricultural University, Kunming, 650201, China; Key Laboratory of Medicinal Plant Biology of Yunnan Province, Yunnan Agricultural University, Kunming, 650201, China; National & Local Joint Engineering Research Center on Germplasm Innovation & Utilization of Chinese Medicinal Materials in Southwestern China, Yunnan Agricultural University, Kunming, 650201, China.
Gene. 2024 Apr 5;901:148163. doi: 10.1016/j.gene.2024.148163. Epub 2024 Jan 13.
Nitrogen (N) is an important macronutrient involved in the biosynthesis of primary and secondary metabolites in plants. However, the metabolic regulatory mechanism of low-N-induced triterpenoid saponin and flavonoid accumulation in rhizomatous medicinal Panax notoginseng (Burk.) F. H. Chen remains unclear.
To explore the potential regulatory mechanism and metabolic basis controlling the response of P. notoginseng to N deficiency, the transcriptome and metabolome were analysed in the roots.
The N content was significantly reduced in roots of N-treated P. notoginseng (0 kg·N·667 m). The C/N ratio was enhanced in the N-deficient P. notoginseng. N deficiency promotes the accumulation of amino acids (L-proline, L-leucine, L-isoleucine, L-norleucine, L-arginine, and L-citrulline) and sugar (arabinose, xylose, glucose, fructose, and mannose), thus providing precursor metabolites for the biosynthesis of flavonoids and triterpenoid saponins. Downregulation of key structural genes (PAL, PAL3, ACC1, CHS2, PPO, CHI3, F3H, DFR, and FGT), in particular with the key genes of F3H, involved in the flavonoid biosynthesis pathway possibly induced the decrease in flavonoid content with increased N supply. Notoginsenoside R, ginsenoside Re, Rg, Rd, F, R + Rg + Rb and total triterpenoid saponins were enhanced in the N groups than in the N (15 kg·N·667 m) plants. Higher phosphoenolpyruvate (an intermediate of glycolyticwith pathway metabolism) and serine (an intermediate of photorespiration) levels induced by N deficiency possibly promote saponin biosynthesis through mevalonic acid (MVA) and methylerythritol (MEP) pathways. Genes (MVD2, HMGS, HMGR1, HMGR2, DXR, and HMGR1) encoding the primary enzymes HMGS, HMGR, DXR, and MVD in the MVA and MEP pathways were significantly upregulated in the N-treated P. notoginseng. The saponin biosynthesis genes DDS, DDS, CYP716A52, CYP716A47, UGT74AE2, and FPS were upregulated in the N-deficient plants. Upregulation of genes involved in saponin biosynthesis promotes the accumulation of triterpenoid saponins in the N-grown P. notoginseng.
N deficiency enhances primary metabolisms, such as amino acids and sugar accumulation, laying the foundation for the synthesis of flavonoids and triterpenoid saponins in P. notoginseng. F3H, DDS, FPS, HMGR, HMGS and UGT74AE2 can be considered as candidates for functional characterisation of the N-regulated accumulation of triterpenoid saponins and flavonoids in future.
氮（N）是植物中初级和次级代谢物生物合成的重要大量营养素。然而，氮缺乏诱导的根茎状药用西洋参（Panax notoginseng（Burk.）F. H. Chen）三萜皂苷和类黄酮积累的代谢调控机制仍不清楚。
为了探讨控制西洋参对氮缺乏反应的潜在调控机制和代谢基础，对根进行了转录组和代谢组分析。
在施氮的西洋参（0 kg·N·667 m）根中，N 含量显著降低。在缺氮的西洋参中，C/N 比增加。氮缺乏促进氨基酸（L-脯氨酸、L-亮氨酸、L-异亮氨酸、L-正亮氨酸、L-精氨酸和 L-瓜氨酸）和糖（阿拉伯糖、木糖、葡萄糖、果糖和甘露糖）的积累，从而为类黄酮和三萜皂苷的生物合成提供前体代谢物。关键结构基因（PAL、PAL3、ACC1、CHS2、PPO、CHI3、F3H、DFR 和 FGT）的下调，特别是参与类黄酮生物合成途径的 F3H 关键基因，可能导致在氮供应增加时类黄酮含量下降。在 N 组中，与 N（15 kg·N·667 m）植株相比，人参皂苷 R、人参皂苷 Re、Rg、Rd、F、R+Rg+Rb 和总三萜皂苷增加。氮缺乏诱导的磷酸烯醇丙酮酸（糖酵解途径的中间产物）和丝氨酸（光呼吸中间产物）水平升高，可能通过甲羟戊酸（MVA）和甲基赤藓醇（MEP）途径促进皂苷生物合成。在施氮的西洋参中，MVA 和 MEP 途径中编码主要酶 HMGS、HMGR、DXR 和 MVD 的基因（MVD2、HMGS、HMGR1、HMGR2、DXR 和 HMGR1）显著上调。在氮缺乏的植物中，皂苷生物合成基因 DDS、DDS、CYP716A52、CYP716A47、UGT74AE2 和 FPS 上调。皂苷生物合成相关基因的上调促进了三萜皂苷在 N 生长的西洋参中的积累。
氮缺乏增强了氨基酸和糖等初级代谢物的积累，为西洋参中类黄酮和三萜皂苷的合成奠定了基础。F3H、DDS、FPS、HMGR、HMGS 和 UGT74AE2 可作为未来研究氮调控三萜皂苷和类黄酮积累的功能特征的候选基因。
