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

在过去的十年中，植物如何识别病原体并进行防御反应一直是研究的重点，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，它是番茄抗性基因Cf-2识别产生AVR2的致病真菌所必需的。Cf2蛋白似乎“保护”RCR3以监测AVR2对其的抑制（guard模型）。然而，我们最近的数据显示，AVR2还抑制了一种更丰富的蛋白酶PIP1，这表明PIP1是AVR2的有效靶点，而RCR3充当诱饵，诱骗真菌进入识别事件（诱饵模型）。此外，我们发现来自细菌和卵菌界的番茄病原体也能产生针对RCR3和相关蛋白酶的抑制剂，并且这些抑制剂所针对的蛋白酶处于多样化选择中。这些数据表明RCR3和相关蛋白酶在防御和识别来自不同王国的病原体中发挥重要作用。该提案涉及一系列简单的病原体分析和抑制实验，将用于确定：1)RCR3和其他蛋白酶在植物与病原体相互作用中的作用（测试Guard和Decoy模型）；2) RCR3和其他蛋白酶的变体残基在抑制和识别AVR2和其他抑制剂中的作用；3)利用抑制剂不敏感的蛋白酶和改进的病原体来源抑制剂传感器测试作物保护的新方法。因此，通过一系列直接可行的检测，并通过与sophia Kamoun博士（Sainsbury实验室，Norwich， UK）的富有成效的合作，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.