异氯酸盐衍生的代谢能够生物合成植物防御激素水杨酸(SA)及其衍生物。在拟南芥中,应力诱导的SA积累取决于异磷酸合成酶1(ICS1),并且还需要假定的等氯酸盐转运蛋白增强的疾病易感性5(EDS5)和GH3酶avrPphB易感性3(PBS3)。通过比较代谢物和结构分析,我们确定了几个迄今未报告的ICS1和EDS5依赖性,生物胁迫诱导的拟南芥代谢产物。这些涉及间位取代的SA衍生物(5-甲酰基-SA,5-羧基-SA,5-羧甲基-SA),他们的苯甲酸(BA)类似物(3-甲酰-BA,3-羧基-BA,3-羧甲基-BA)和,除了先前检测到的水杨酰基天冬氨酸(SA-Asp),酯共轭水杨酰基苹果酸酯(SA-Mal)。SA作为SA-Mal和SA-Asp的生物合成前体,但不是对间位取代的SA和BA衍生物,在细菌感染的后期积累到中等水平。有趣的是,拟南芥叶具有氧化活性以有效地将间甲酰转化成间羧基-SA/BA。与SA相比,外源应用的间位取代的SA/BA衍生物和SA-Mal对植物免疫和防御相关基因表达产生中等影响。虽然异分支酸盐衍生的代谢产物受到PRGENES1的SA受体非表达的负调控,但SA缀合物(SA-Mal,SA-Asp,SA-葡萄糖缀合物)和间位取代的SA/BA衍生物受PBS3的相反影响。值得注意的是,我们的数据表明,在细菌感染的后期阶段,PBS3独立于等分支酸盐衍生的SA的路径,这不会显着影响免疫相关的特征。此外,我们的结果与先前提出的EDS5在免疫信号N-羟基羧酸的生物合成和相关转运过程中的作用相反。我们提出了一种显着扩展的植物异氯酸盐代谢生化方案,该方案涉及苯甲酸酯和水杨酸酯衍生物的替代生成模式。
Isochorismate-derived metabolism enables biosynthesis of the plant defence hormone salicylic acid (SA) and its derivatives. In Arabidopsis thaliana, the stress-induced accumulation of SA depends on ISOCHORISMATE SYNTHASE1 (ICS1), and also requires the presumed isochorismate transporter ENHANCED DISEASE SUSCEPTIBILITY5 (EDS5) and the GH3 enzyme avrPphB SUSCEPTIBLE3 (PBS3). By comparative metabolite and structural analyses, we identified several hitherto unreported ICS1- and EDS5-dependent, biotic stress-inducible Arabidopsis metabolites. These involve meta-substituted SA derivatives (5-formyl-SA, 5-carboxy-SA, 5-carboxymethyl-SA), their benzoic acid (BA) analogues (3-formyl-BA, 3-carboxy-BA, 3-carboxymethyl-BA) and, besides the previously detected salicyloyl-aspartate (SA-Asp), the ester conjugate salicyloyl-malate (SA-Mal). SA functions as a biosynthetic precursor for SA-Mal and SA-Asp, but not for the meta-substituted SA- and BA-derivatives, which accumulate to moderate levels at later stages of bacterial infection. Interestingly, Arabidopsis leaves possess oxidising activity to effectively convert meta-formyl- into meta-carboxy-SA/BAs. In contrast to SA, exogenously applied meta-substituted SA/BA-derivatives and SA-Mal exert moderate impact on plant immunity and defence-related gene expression. While the isochorismate-derived metabolites are negatively regulated by the SA receptor NON-EXPRESSOR OF PR GENES1, SA conjugates (SA-Mal, SA-Asp, SA-glucose conjugates) and meta-substituted SA/BA-derivatives are oppositely affected by PBS3. Notably, our data indicate a PBS3-independent path to isochorismate-derived SA at later stages of bacterial infection, which does not considerably impact immune-related characteristics. Moreover, our results argue against a previously proposed role of EDS5 in the biosynthesis of the immune signal N-hydroxypipecolic acid and associated transport processes. We propose a significantly extended biochemical scheme of plant isochorismate metabolism that involves an alternative generation mode for benzoate- and salicylate-derivatives.