Wang Ning, Wang Long, Qi Lianwen, Lu Xu
State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, People's Republic of China.
Biotechnol Appl Biochem. 2018 Mar;65(2):119-127. doi: 10.1002/bab.1580. Epub 2017 Sep 12.
Triterpene saponins are main active constituents of Panax notoginseng. Metabolites profiling of 12 triterpene saponins was analyzed by high-performance liquid chromatography-mass spectrometry in leaf, petiole, and root extracts of P. notoginseng. Most of the 20(S)-protopanaxatriol (PPT) type saponins, except ginsenoside Re, were mainly distributed in roots, while 20(S)-protopanaxadiol (PPD) type saponins were detected among various tissues. The total content of PPD-type saponins decreased in the order of leaf, petiole, and root. The expression patterns of four key genes (PnFPS, PnSQS, PnDS, and PnSE) in the triterpene saponin biosynthetic pathway were measured by real-time quantitative PCR (RT-qPCR). All the four investigated genes showed high expression levels in leaf. A gene-to-metabolite network was constructed through canonical correlation analysis. The results indicated that the expression levels of PnFPS, PnSQS, PnDS, and PnSE had high correlation with PPD-type saponins ginsenoside Rb , Rb , and Rc, while PnSQS was also highly correlated with Rb . Combining metabolic profiling, RT-qPCR, and gene-to-metabolite network, we inferred that the leaf of P. notoginseng was the main biosynthesis site of PPD-type saponins Rb , Rb , and Rc. The contribution to the biosynthesis of ginsenosides Rb , Rb , and Rc was in the order of PnSE > PnDS > PnSQS > PnFPS. PnSE and PnDS should be the preferred targets to regulate the production of PPD-type saponins Rb , Rb , and Rc in P. notoginseng by plant metabolic engineering.
三萜皂苷是三七的主要活性成分。采用高效液相色谱 - 质谱联用技术分析了三七叶、叶柄和根提取物中12种三萜皂苷的代谢物谱。除人参皂苷Re外，大多数20(S)-原人参三醇（PPT）型皂苷主要分布在根中，而20(S)-原人参二醇（PPD）型皂苷在各组织中均有检测到。PPD型皂苷的总含量按叶、叶柄和根的顺序递减。通过实时定量PCR（RT-qPCR）检测了三萜皂苷生物合成途径中4个关键基因（PnFPS、PnSQS、PnDS和PnSE）的表达模式。所研究的4个基因在叶中均表现出高表达水平。通过典型相关分析构建了基因 - 代谢物网络。结果表明，PnFPS、PnSQS、PnDS和PnSE的表达水平与PPD型皂苷人参皂苷Rb₁、Rb₂和Rc高度相关，而PnSQS也与Rb₃高度相关。结合代谢物谱分析、RT-qPCR和基因 - 代谢物网络，我们推断三七叶是PPD型皂苷Rb₁、Rb₂和Rc的主要生物合成部位。对人参皂苷Rb₁、Rb₂和Rc生物合成的贡献顺序为PnSE＞PnDS＞PnSQS＞PnFPS。通过植物代谢工程调控三七中PPD型皂苷Rb₁、Rb₂和Rc的产量时，PnSE和PnDS应作为首选靶点。
