Elucidation of steroidal backbone synthesis for plant defensive mechanisms

我们假设番茄中的一部分番茄碱（一种甾体生物碱）是通过羊毛甾醇生物合成的，并且番茄碱含量通过MeJA处理增强羊毛甾醇途径而增加。为了研究茉莉酸甲酯（MeJA）诱导番茄碱含量的变化，将番茄幼苗在含有5μM茉莉酸甲酯的MS培养基中培养1、3和7 d。收获幼苗，提取并进行番茄碱的定量LC-MS分析。番茄碱的含量比未处理的幼苗高4倍，而胆固醇和植物甾醇的含量保持不变。此外，还进行了[ 6-^C^2H_3<13>] MVL对番茄幼苗的饲喂实验，并对番茄碱的骨架合成进行了~ 1H-NMR分析<13>。结果发现，在正常生长条件下，环阿屯醇途径是一种具有很少或没有羊毛留醇途径的唯一途径。通过5μM MeJA处理，羊毛甾醇途径对番茄碱生物合成的贡献增加至约100%。3%的环阿屯醇途径。然而，在这两种条件下，甾醇通过环阿屯醇途径生物合成，很少或没有羊毛甾醇途径。从这些结果，它表明，番茄碱生物合成的增加发生独立的植物甾醇生物合成。

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.