Elucidation of steroidal backbone synthesis for plant defensive mechanisms

我们推测番茄中的甾体生物碱——番茄素的一部分是通过羊毛甾醇进行生物合成的，MeJA处理增强了羊毛甾醇途径，从而提高了番茄素的含量。为了研究MeJA诱导下番茄含量的变化，将番茄幼苗在含5μM MeJA的MS培养基中培养1d、3d和7d。幼苗收获，提取，并进行定量LC-MS分析番茄。番茄素含量比未处理幼苗高4倍，而胆固醇和植物甾醇含量保持不变。此外，还利用番茄幼苗进行了[6-^<13> ^C ^2H_3] MVL的投料实验，并利用<13>^C- nmr分析了番茄碱的骨架合成。结果表明，在正常生长条件下，环蒿烯醇途径是一条与羊毛甾醇途径很少或没有的唯一途径。通过5μM MeJA处理，羊毛甾醇途径对番茄素生物合成的贡献增加到环青蒿醇途径的约3%。然而，在两种条件下，甾醇都是通过环青蒿醇途径合成的，很少或没有羊毛甾醇途径。从这些结果来看，番茄素生物合成的增加是独立于植物甾醇生物合成的。

We hypothesized that a part of tomatine, a steroidal alkaloid in tomato, is biosynthesized via lanosterol, and tomatine content is increased by enhancing lanosterol pathway with MeJA treatment. In order to investigate the variation of tomatine content by the elicitation with MeJA, tomato seedlings were incubated for 1d, 3d, and 7d in MS medium including 5μM MeJA. The seedlings were harvested, extracted and subjected to quantitative LC-MS analysis for tomatine. The content of tomatine was 4-fold higher than in the untreated seedlings, while the contents of cholesterol and phytosterol were held constant. In addition, the feeding experiments of[ 6-^<13> C^2H_3] MVL were performed using tomato seedlings and the backbone synthesis of tomatine was analyzed by<13>^C-NMR. As a result, the cycloartenol pathway was found to be an exclusive route with little or no lanosterol pathway in a normal growth condition. By 5μM MeJA treatment the contribution of the lanosterol pathway to tomatine biosynthesis was increased up to ca. 3% of the cycloartenol pathway. However the sterols were biosynthesized by the cycloartenol pathway with little or no lanosterol pathway in the both conditions. From these results, it is suggested that an increase in tomatine biosynthesis occurs independently of phytosterol biosynthesis.