Transcriptional regulation in effector-triggered immunity via NB-LRR resistance genes RPS4 & RRS1

农作物容易受到由各种微生物引起的疾病的影响，这些疾病可能会导致大量的产量损失。农民喷洒农用化学品来控制疾病；这是昂贵的，需要燃料和劳动力，并导致土壤压实。作物最好是抗病的，这样就不需要使用杀菌剂了。实现这一目标需要更多的知识。育种者使用抗病(R)基因进行作物改良；育种者不断需要更多的R基因，因为病原体可以进化来克服它们。R基因赋予病原菌毒力促进分子(所谓的“效应器”)的识别能力，这些分子对毒力有贡献。R基因的持久性各不相同；更持久的R基因很可能识别病原体最不可或缺的效应因子。植物抗病还涉及对保守的病原菌分子模式的反应--“模式触发免疫(PTI)”。尽管PTI和R基因介导的抗性反应存在重叠，但它们之间的机制联系仍然完全不清楚。要想在未来的作物中持久抗病，我们需要深入了解病原菌的毒力和寄主防御机制。这需要了解效应器的宿主靶标的光谱，了解植物R蛋白如何(直接或间接)识别效应器的存在，以及在识别后如何激活防御机制，从而导致宿主植物免疫。植物R蛋白与哺乳动物结节样受体(NLRs)相似，NLRs参与哺乳动物的先天免疫；例如，克罗恩病是由人类NOD2基因缺陷引起的。NLR的信号机制也不完全清楚。NOD2和Nb-LRR蛋白携带相似的蛋白质模块，具有N端信号域、中央核苷酸结合(NB)结构域和C末端富含亮氨酸重复(LRR)结构域。这项工作将有助于我们更好地了解植物的抗性机制。我们将在模式植物拟南芥中研究一个有趣的抗病基因座，它对两种不同的细菌物种产生抗性，这两种细菌引起细菌斑点或青枯病，也对一种真菌病原体产生抗性。该基因座包含两种不同的NB-LRR R蛋白，RRS1和RPS4，它们彼此转录分离，这两个蛋白都是抗病所必需的。RPS4和RRS1还携带一个所谓的TIR结构域，与人和苍蝇的免疫受体共享。RRS1有一个额外的结构域(“WRKY”结构域)，已被证明与DNA结合，并可能调节参与植物防御的基因的表达。RPS4/RRS1在识别细菌斑点中的AvrRps4效应蛋白、青枯病中的PopP2效应蛋白或真菌病原菌Colletotrichum higginsianum时激活防御。这是如何发挥作用的，仍然是一个谜。-我们希望了解RPS4/RRS1在识别AvrRps4或PopP2时如何激活参与防御的基因的表达。我们将研究RRS1的DNA结合域靶向的DNA序列，并将相应的基因与RPS4/RRS1防御激活时诱导的基因以及PTI过程中诱导的基因进行比较。通过这种方式，我们将确定RPS4/RRS1的直接靶标以及当被激活时导致抗药性的基因。这将使我们能够建立一幅通过R蛋白触发的阻止病原体生长的事件链的图景。-一旦我们从这些研究中获得所有数据，我们将能够提出和测试在防御激活过程中发生的模型，使该系统成为最被理解的R基因系统之一；这些知识将为试图扩大R基因识别能力的方法提供信息，从而增强其实用性和持久性。

Crop plants are subject to diseases caused by various microbes that can cause substantial yield losses. Farmers spray agrochemicals to control disease; this is expensive, requires fuel and labour, and leads to soil compaction. It would be preferable for crops to be disease resistant, so that no fungicide applications are required. More knowledge is required to achieve this goal. Breeders use disease resistance (R) genes for crop improvement; more R genes are continuously needed by breeders, because pathogens can evolve to overcome them. R genes confer recognition of pathogen virulence-promoting molecules (so-called "effectors") that contribute to virulence. R gene durability varies; it is likely that more durable R genes recognize the most indispensable effectors for the pathogen. Plant resistance also involves responses to conserved pathogen molecular patterns- "pattern-triggered immunity (PTI)". Although there is overlap in PTI and R gene-mediated resistance responses, the mechanistic link between them is still completely obscure.For durable resistance in our future crops, we need a deep understanding of pathogen virulence and host defence mechanisms. This requires knowledge of the spectrum of host targets of effectors, of how plant R proteins recognize (directly or indirectly) the presence of effectors, and of how upon recognition, defence mechanisms are activated that result in host plant immunity. Plant R proteins resemble mammalian Nod-like receptors (NLRs) that are involved in mammalian innate immunity; for example, Crohn's disease results from a defect in the human NOD2 gene. Mechanisms of NLR signalling are also incompletely understood. NOD2 and NB-LRR proteins carry similar protein modules, with an N-terminal signalling domain, a central nucleotide-binding (NB) domain and a C-terminal leucine-rich repeat (LRR) domain. The proposed work will help us better understand mechanisms of plant resistance. We will study a fascinating disease resistance locus in the model plant Arabidopsis that confers resistance to two distinct bacterial species that cause either bacterial speck or bacterial wilt, and also confers resistance to a fungal pathogen. This locus contains two different NB-LRR R proteins, RRS1 and RPS4, that are transcribed away from each other, and both of which are required for resistance. RPS4 and RRS1 also carry a so-called TIR domain shared with immune receptors of humans and flies. RRS1 has an additional domain (a "WRKY" domain) that has been shown to bind DNA, and that could regulate expression of genes involved in plant defence. RPS4/RRS1 activates defence upon recognizing AvrRps4 effector protein from bacterial speck, or PopP2 effector protein from bacterial wilt, or the fungal pathogen Colletotrichum higginsianum. How this works is still a mystery. - We wish to understand how RPS4/RRS1 activates expression of genes involved in defence upon recognition of AvrRps4 or PopP2. We will investigate the DNA sequences targeted by the DNA binding domain of RRS1, and compare the corresponding genes to the genes that are induced upon RPS4/RRS1 defence activation, and to genes induced during PTI. In this way we will define the direct targets of RPS4/RRS1 and the genes that when activated result in resistance. This will enable us to build up a picture of the chain of events triggered via R proteins that stop the pathogen from growing.- Once we have all the data from these investigations we will be able to propose and test models for what takes place during defence activation, making this system one of the best understood R gene systems; this knowledge will inform approaches to attempting to broaden the recognition capacity of R genes, to thus enhance their utility and durability.