RLP and RLK-mediated innate immune responses in Arabidopsis and tomato triggered by PAMPS and Avrs

植物对病害的抗性或易感性主要包括3个组成部分。首先，许多微生物产生病原体相关分子模式(PAMPs)，如细菌鞭毛蛋白和真菌甲壳素，植物已经进化出识别和响应的能力。这会导致PAMP触发的免疫(PTI)。其次，许多病原体制造并传递给植物细胞的效应蛋白干扰PTI，降低防御活性，导致敏感性。第三，植物有一套抗性(R)基因，这些基因编码的传感器蛋白可以直接识别特定的病原体效应器，也可以通过效应器对宿主成分的作用间接识别。R基因依赖的识别导致效应器触发免疫(ETI)，恢复抗性。为了了解抗性，我们需要更好地了解PTI，这不仅是因为它的内在兴趣和在作物保护中的重要作用，还因为PTI涉及的寄主成分是病原菌效应分子的靶标。我们还需要知道ETI和PTI是否涉及相同的机制。通过研究鞭毛蛋白的多肽替代物flg22的反应，已在拟南芥中研究了PTI。防御激活需要一个与flg22结合的跨膜受体Fls2，它与蛋白激酶激活、活性氧产生、细胞壁加固和基因诱导有关。这一建议的主要目的是1)用正向遗传学来理解PTI，2)用反向遗传学来理解细胞表面受体在激活植物免疫系统中的作用。基因分析提供了一种更严格的测试，以确定所研究的过程是否确实需要相关现象。在正向遗传方法中，寻找感兴趣的过程失活的突变；这种突变存在于该过程所需的基因中。拟南芥也对另一种名为EF-Tu的细菌PAMP蛋白及其相应的多肽替代品elf18做出反应。Elf18通过另一种称为EFR的跨膜受体触发与flg22非常相似的反应。然而，elf18可以在较低的剂量下使用，从而实现了一个包含100个数千个突变种子的拟南芥突变筛选，在这个筛选中，每个基因都将被“击中”数十次。这使得能够恢复具有微妙影响的罕见的新等位基因，这往往为生物机制提供了最微妙和最有趣的新见解。在反向遗传方法中，突变体将被用来研究受体蛋白在识别卵菌病原体中的作用，包括甘蓝的霜霉病和白锈病以及马铃薯和番茄的晚疫病病原菌。我们的初步数据表明，这些细胞表面受体蛋白中的一些可能起到了作用。我们期待这一研究项目将为受体蛋白如何工作提供深刻的机制洞察。它还将识别识别后编码信号所需蛋白质的基因。研究这些基因是由多个激发子触发的PTI所必需的，还是仅仅由elf18触发的，这将是非常有趣的。可以想象，这样的突变体将在对由真菌和细菌引起的许多病原体的抗病能力方面受到损害；这种可能性将得到测试。许多生化现象与PTI相关--这些现象将在不同的突变体中进行检查，看看它们是否差异地使一些但不是全部elf18反应失效。最后，将通过标准的基于图谱的克隆方法分离单独的elf18或从多个PAMP中发出信号所需的基因，然后进行进一步的检查。

Plant resistance or susceptibility to disease primarily involves 3 components. Firstly, many microbes make Pathogen-Associated Molecular Patterns (PAMPs), such as bacterial flagellin and fungal chitin, which plants have evolved the capacity to recognize and respond to. This results in PAMP-triggered immunity (PTI). Secondly, many pathogens make and deliver to plant cells, effector proteins that interfere with PTI, lowering defence activation, resulting in susceptibility. Thirdly, plants have a repertoire of resistance (R) genes that encode sensor proteins that recognize specific pathogen effectors, either directly, or indirectly via effector action on a host component. R gene-dependent recognition results in effector-triggered immunity (ETI), restoring resistance. To understand resistance, we need to better understand PTI, not only because of its intrinsic interest and important role in crop protection, but also because host components involved in PTI are targets of pathogen effectors. We also need to know whether ETI and PTI involve the same mechanisms. PTI has been studied in Arabidopsis by investigating responses to flg22, a peptide surrogate of flagellin. Defence activation requires a transmembrane receptor FLS2 that binds flg22, and is correlated with protein kinase activation, reactive oxygen species production, cell wall fortification and gene induction. The main aim of this proposal is 1) to use forward genetics to understand PTI and 2) to use reverse genetics to understand the role of cell surface receptors in activating the immune system of plants. Genetic analysis provides a more stringent test of whether or not a correlated phenomenon is actually required for the process under study. In a forward genetic approach, mutants are sought in which the process of interest is inactivated; such mutations are in genes required for that process. Arabidopsis also responds to another bacterial PAMP protein called EF-Tu, and to its corresponding peptide surrogate elf18. Elf18 triggers, via another transmembrane receptor called EFR, a very similar response to flg22. However, elf18 can be used at lower doses, enabling an Arabidopsis mutant screen that involves 100s of thousands mutagenized seeds, in which every gene will have been 'hit' scores of times. This enables recovery of rare new alleles of genes with subtle effects, which often provide the most subtle and interesting new insights into biological mechanisms. In a reverse genetic approach, mutants will be used to investigate the role of receptor proteins in recognition of oomycete pathogens including downy mildew and white rusts of brasssicas and late blight pathogen of potato and tomato. Our initial data suggests that some of these cell surface receptor proteins may play a role. We anticipate that this research program will provide profound mechanistic insights into how the receptor proteins work. It will also identify genes encoding proteins required for signalling after recognition. It will be very interesting to examine whether these genes are required for PTI triggered by multiple elicitors or just elf18. Conceivably, such mutants will be compromised in disease resistance to many pathogens, caused by fungi as well as bacteria; this possibility will be tested. Many biochemical phenomena are correlated with PTI- these will be examined in the various mutants, to see if they differentially disable some but not all elf18 responses. Finally, genes required for signalling for either elf18 alone, or from multiple PAMPs, will be isolated by standard map-based cloning methods and then further examined.