Tomato cysteine proteases and pathogen-derived inhibitors: the molecular arms-race towards defense and recognition

在过去的十年里，植物如何识别病原体和防御反应一直是人们深入研究的主题，产生了重要的工作模型，如Guard模型，该模型解释了抗性基因产物在基因对基因相互作用中的间接感知机制。其中一个关键的例子是番茄蛋白酶RCR3，它是通过番茄抗性基因CF-2识别产生AVR2的病原真菌所必需的。CF2蛋白似乎守卫着RCR3，通过AVR2(Guard Model)监控其抑制。然而，我们最近的数据表明，AVR2也抑制了一种更丰富的名为PIP1的蛋白酶，这表明PIP1是AVR2的操作靶标，而RCR3作为诱饵将真菌捕获到识别事件中(诱饵模型)。此外，我们还发现，来自细菌界和卵菌界的番茄病原菌也会产生针对RCR3和相关蛋白酶的抑制剂，这些抑制剂针对的蛋白酶正在进行多样化的选择。这些数据表明，RCR3和相关的蛋白酶在防御和识别来自不同王国的病原体方面发挥了重要作用。这项建议涉及一系列简单的病原体分析和抑制实验，这些实验将被用来确定：1)RCR3和其他蛋白酶在植物-病原体相互作用中的作用(测试卫士和诱饵模型)；2)RCR3和其他蛋白酶的变异残基在抑制和识别AVR2和来自其他王国的抑制剂方面的作用；3)测试使用抑制剂不敏感的蛋白酶和改进的病原衍生抑制剂传感器来保护作物的新方法。因此，通过一系列简单、可行的分析，并通过继续与索芬·卡蒙博士(英国诺里奇的塞恩斯伯里实验室)进行卓有成效的合作，该项目旨在为当前分子植物病理学中的许多关键问题提供答案。

The way how plants recognize pathogens and mount defense responses has been subject of intense research over the past decade, resulting in important working models such as the Guard Model, which explains the indirect perception mechanism by resistance gene products in gene-for-gene interactions. One of the key examples is tomato protease RCR3, which is required for recognition of pathogenic fungi producing AVR2 by the tomato resistance gene Cf-2. The Cf2 protein seems to ‘guard’ RCR3 to monitor its inhibition by AVR2 (Guard Model). However, our recent data showed that AVR2 also inhibits a more abundant protease called PIP1, suggesting that PIP1 is the operative target of AVR2 and that RCR3 acts as a decoy to trap the fungus into a recognition event (Decoy Model). In addition, we found that tomato pathogens from bacterial and oomycete kingdoms also produce inhibitors that can target RCR3 and related proteases, and that the proteases targeted by these inhibitors are under diversifying selection. These data suggest an important role for RCR3 and related proteases in defense and recognition of pathogens from different kingdoms. This proposal concerns a series of simple pathogen assays and inhibition experiments that will be used to determine: 1) the role of RCR3 and other proteases in plant-pathogen interactions (testing Guard and Decoy Models); 2) the role of variant residues in RCR3 and other proteases in inhibition and recognition of AVR2 and inhibitors from other kingdoms; 3) test novel ways of crop protection using inhibitor-insensitive proteases and improved sensors for pathogen-derived inhibitors. Thus, with a series of straightforward, feasible assays and through a continuation of a fruitful collaboration with Dr. Sophien Kamoun (Sainsbury lab, Norwich, UK), this project aims to deliver answers to many of the current key questions in molecular plant pathology.