MOB proteins as novel regulators of pathogen-associated molecular pattern-triggered immunity in Arabidopsis thaliana

植物和动物一样，利用表面定位的受体来感知质外体中的微生物蛋白，并触发称为病原体相关分子模式（PAMP）触发免疫（PTI）的早期免疫反应。这类受体的典型实例是受体激酶FLS 2和EFR，它们分别结合细菌PAMP鞭毛蛋白和延伸因子-Tu。由FLS 2和EFR介导的免疫依赖于辅助受体BAK 1，其在配体结合后立即与主要受体异聚化。尽管最近的进展，发生在受体激活下游的信号事件仍然难以捉摸。拟议的研究利用宿主实验室提供的独特工具，利用最近在模式植物拟南芥中新的正向遗传筛选中发现的突变体，揭示PTI的遗传机制。该筛选利用了新的突变体bak 1 -5，其在PTI中特异性受损，但不表现出通常在bak 1无效突变体中观察到的其他多效性表型。本研究旨在研究bak 1 -5（mob）突变体的修饰物及其蛋白质。mob突变体恢复了bak 1 -5突变体背景下PAMP触发的反应，包括对细菌的免疫力。初步数据表明，一个突变体影响枯草杆菌蛋白酶样丝氨酸蛋白酶S1 P，这是以前被证明在不同的生物途径处理前肽。一个重要的实例是前肽的切割导致RALF 23肽的释放。值得注意的是，宿主实验室中的生物信息学分析将编码RALF 23的基因鉴定为flg 22依赖性基因表达网络中的关键枢纽，因此表明该肽在PTI信号传导中的功能。RALF 23属于一个包括RALF 33和根特异性RALF 1的3成员基因簇。有趣的是，RALF 1最近被证明是由RK FERONIA（FER）感知的，值得注意的是，FER突变体显示出增加的flg 22触发的ROS爆发和增强的对假单胞菌感染的抗病性。因此，我们的工作模型是S1 P切割PRORALF 23和/或PRORALF 33以释放活性肽，该活性肽又与FER（或相关蛋白）结合，导致PTI信号传导的抑制，这表明PTI调节的先前未知机制。这项研究计划的主要目标是挑战这一新颖而令人兴奋的假设。

Plants, like animals, utilize surface-localized receptors to sense microbial proteins in the apoplast and trigger an early immune response known as pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). Archetypal examples of such receptors are the receptor kinases FLS2 and EFR, which bind the bacterial PAMPs flagellin and elongation factor-Tu, respectively. Immunity mediated by FLS2 and EFR depends on the co-receptor BAK1 that heteromerizes with the main receptors immediately following ligand binding. Despite recent advances, the signalling events that occur downstream of receptor activation remain elusive. The proposed research takes advantage of unique tools available in the host laboratory to uncover the genetic mechanisms underlying PTI using mutants recently identified in a novel forward-genetic screen in the model plant Arabidopsis thaliana. This screen utilized the novel mutant bak1-5, which is specifically impaired in PTI but does not exhibit other pleiotropic phenotypes normally observed in bak1 null mutants. This proposal aims at characterizing modifier of bak1-5 (mob) mutants and corresponding proteins. The mob mutants restore PAMP-triggered responses in the bak1-5 mutant background, including immunity to bacteria. Preliminary data suggest that one mutant affects the subtilisin-like serine protease S1P, which was previously shown to process propeptides in different biological pathways. An important example is the cleavage of the pro-peptide leading to the release of the RALF23 peptide. Notably, bioinformatics analysis in the host lab identified the gene encoding RALF23 as a key hub in an flg22-dependent gene expression network and therefore indicating a function of this peptide in PTI signalling. RALF23 belongs to a 3-member gene cluster including RALF33 and the root-specific RALF1. Interestingly, RALF1 was recently shown to be perceived by the RK FERONIA (FER) and, notably, fer mutants show an increased flg22-triggered ROS burst and enhanced disease resistance to Pseudomonas syringae infections. Therefore, our working model is that S1P cleaves PRORALF23 and/or PRORALF33 to release the active peptide, which in turn binds to FER (or a related protein) resulting in the inhibition of PTI signalling, suggesting a previously unknown mechanism for the regulation of PTI. The main goal of this research proposal is to challenge this novel and exciting hypothesis.