Metabolism and signal transduction of the plant immune signal pipecolic acid

我们之前的工作揭示了赖氨酸衍生的植物代谢物pipecolic acid （Pip）在系统性获得性抗性（SAR）和SAR相关的防御启动现象中的关键功能。在本项目的第一期，我们定义了免疫信号Pip和水杨酸在激活植物防御反应和抗性中的相互作用。此外，我们证明了植物中l -赖氨酸的生物合成是通过两个生化过程进行的。α - l -赖氨酸氨基转移酶ALD1催化l -赖氨酸转化为2,3-脱氢果酸，随后还原为Pip。还原步骤涉及植物还原酶ORNCD1/SARD4的作用。此外，我们在体外和植物中阐明了SAR调节因子FMO1作为Pip N-羟化酶的生化功能，该酶催化L-Pip生成N-羟基果酸（Pip- oh）。外源Pip-OH弥补了fmo1突变体植物的免疫缺陷，并作为一种有效的增强植物抵抗细菌和卵菌病原体感染的化合物。在下一个项目阶段，我们的目标是进一步推进对拟南芥中Pip代谢途径的理解。我们将从生物化学和功能上研究Pip生物合成的还原步骤和Pip- oh的糖基化。通过结合LC-MS-， NMR-和GC-MS-based分析方法，我们旨在鉴定和表征迄今未知的参与Pip代谢途径的代谢物。对免疫调节因子NPR1作用的基因筛选和靶向研究将揭示Pip-OH积累下游的免疫信号过程。Pip在SAR长距离信号传导中的意义分析已经在第一个项目阶段开始，将通过使用遗传方法继续进行，并在此过程中扩展到羟基化Pip衍生物的功能。最后，将从细胞学和分子水平研究Pip-OH对卵霉菌感染的抗性增强作用。

Our previous work revealed a critical function for the Lysine-derived plant metabolite pipecolic acid (Pip) in systemic acquired resistance (SAR) and the SAR-associated defense priming phenomenon. In the first period of this project, we have defined the interplay between the immune signals Pip and salicylic acid in the activation of plant defense responses and resistance. Moreover, we showed that the biosynthesis of Pip from L-Lys in plants proceeds via a two-step biochemical process. The alpha-L-Lys-aminotransferase ALD1 catalyzes the conversion of L-Lys to 2,3-dehydropipecolic acid, which is subsequently reduced to Pip. The reductive step involves the action of the plant reductase ORNCD1/SARD4. In addition, we elucidated the biochemical function of the SAR regulator FMO1 as a Pip N-hydroxylase which catalyzes the formation of N hydroxypipecolic acid (Pip-OH) from L-Pip in vitro and in planta. Exogenous Pip-OH complements the immune defects of fmo1 mutant plants and acts as an efficient resistance-enhancing compound in plants towards infection by bacterial and oomycete pathogens. In the next project phase, we aim to further advance the understanding of the Pip metabolic pathway in Arabidopsis. We will biochemically and functionally investigate the reductive step in Pip biosynthesis and the glycosylation of Pip-OH. By using a combination of LC-MS-, NMR-, and GC-MS-based analytical methods, we aim at identifying and characterizing hitherto unknown metabolites involved in Pip metabolic pathway. Both a genetic screen and targeted studies on the role of the immune regulator NPR1 will shed light on the immune signaling processes downstream of Pip-OH accumulation. Analyses of the significance of Pip in SAR long-distance signaling, which had been started in the first project phase, will be continued by using a genetic approach and extended with respect to the function hydroxylated Pip derivatives in this process. Finally, the plant resistance-enhancing action of Pip-OH towards oomycete infection will be investigated at the cytological and molecular levels.