植物天然免疫受体复合物LYK5-CERK1介导几丁质反应的作用机理研究

Plants use cell-surface localized Pattern Recognition Receptors (PRRs) to sense Microbe-Associated Molecular Patterns (MAMPs) activating immunity. This process, which has been termed MAMP-triggered immunity (MTI), serves as an initial defense response against pathogens. Due to the fact that MTI confers a broad-spectrum and durable disease resistance in plants, PRRs could be used to engineer broad-spectrum resistance to a variety of phytopathogens in transgenic plants. Chitin, a fungal cell wall component, triggers immunity via Lysin Motif receptor like protein Kinases (LYKs) in plants. Our recent publication proposed a new model in which chitin is perceived by a protein complex formed by two LYKs, LYK5 and CERK1. In our model, Chitin binds to LYK5 leading to its association with CERK1, dimerization and kinase activation, and in this way, chitin signaling is transduced downstream through CERK1 kinase activity. However, it is not clear how LYK5 is involved in mediating chitin signaling in plants. In this proposal, we will continue to study the phosphorylation between two kinases CERK1 and LYK5, the degradation of LYK5 induced by an E3 ligase, and chitin-induced LYK5 gene expression regulation, and identify of the downstream components through purification of LYK5 protein complex before and after chitin elicitation. Ultimately, our studies will contribute to the understanding of mechanisms of chitin signaling pathway and chitin-induced positive feedback regulation of receptor, providing a high potential for the receptors to be used to engineer broad-spectrum disease resistance in crop plants in future.

微生物相关分子模式激发的植物先天性免疫反应具有广谱性和持久性等特点，过表达相对应的受体基因可明显提高作物对不同病原微生物的抗性。真菌细胞壁成分几丁质是一种重要的微生物相关分子模式，它激发的植物免疫反应由细胞溶素模块膜受体激酶介导。我们前期工作提出一个新模型，即植物对几丁质响应是由两个细胞溶素模块膜受体激酶形成的复合体共同介导的。在这个模型中，LYK5主要介导几丁质的识别和结合，而CERK1负责信号向下游传递。然而，目前还不清楚这一受体复合体介导几丁质反应的分子机理。本课题拟在前期工作的基础上研究CERK1和LYK5之间的磷酸化事件，阐明LYK5的降解机制，通过免疫沉淀纯化LYK5复合体来筛选互作蛋白，并研究信号下游传递的分子机制。旨在从信号转导、信号传递以及受体的正反馈调控等角度获得受体激活免疫反应的新证据，为进一步应用于提高作物的广谱抗病性提供重要的理论依据，本项目具有一定的应用价值。

几丁质真菌细胞壁的主要组成成分，在激发的植物免疫反应中起重要作用。在拟南芥中，两个细胞溶素模块膜受体激酶组成复合物介导了几丁质感受和识别。我们前期工作建立了几丁质受体模型，即CERK1和LYK5组成的复合体共同介导几丁质反应。我们基于此研究结果，发现了二硫键介导的LYK5二聚体是几丁质反应的关键，LYK5受体蛋白受E3泛素连接酶PUB13降解调控，CPK5和CPK6是几丁质受体下游关键组分与受体复合物互作，CPK5和CPK6可以定向磷酸化LYK5从而激活几丁质信号通路。课题从信号转导、信号传递以及受体的正反馈调控等角度研究了拟南芥几丁质激发植物免疫反应的分子机制，为进一步应用于提高作物的广谱抗病性提供重要的理论依据。