Regulation of Pseudomonas syringae Virulence by Plant-Derived Chemical Signals

植物细菌性病害对美国许多重要经济作物的总产量和适销性造成重大损失。虽然植物拥有能够有效抵抗感染的免疫系统，但细菌已经进化出复杂的对抗措施，可以有效地抑制这些宿主的防御。因此，感染结果的主要决定因素是细菌和寄主植物能够多快地部署各自的毒力和防御策略。本项目将研究植物和细菌在感染开始时发生的化学信号事件的分子基础，重点研究致病菌如何感知植物来源的代谢物信号来开始其感染过程。非特异性抗菌剂，如铜喷雾剂和广谱抗生素，经常用于控制作物细菌性疾病。该项目将提供对细菌宿主感知机制的更深入了解，从而可能导致开发该过程的特定化学抑制剂，从而提供控制疾病和潜在提高作物适应性的替代方法。该项目还将为资源有限的小型学院的本科生提供机会，让他们通过在研究者的实验室实习获得研究经验。此外，作为为期两周的高中生STEM夏令营的一部分，研究者将开发并提供关于蛋白质组学方法的研讨会。植物病原体丁香假单胞菌（Pseudomonas syringae）的促毒III型分泌系统（T3SS）编码基因必须在感染的早期表达，才能使这种细菌具有完全的毒力。在之前的工作中，研究者发现了植物来源的代谢物，这些代谢物可以诱导丁香假单胞菌中t3ss编码基因的表达。虽然具有生物活性的植物代谢物是毒力的有效增强剂，但丁香花霉如何感知它们来启动其T3SS的表达尚不清楚。本项目的主要目的是阐明丁香假单胞菌识别宿主的遗传基础，以确定直接参与感知宿主代谢物信号的潜在受体蛋白。第二个目标是阐明为什么超表达其T3SS的丁香假单胞菌gacA-突变体毒性较低，目的是了解丁香假单胞菌如何协调毒力因子的部署以最大化致病性。最后，在丁香假单胞菌侵染拟南芥过程中，外源施用t3ss诱导代谢物抑制了植物病原体识别受体（PRRs）介导的抗性增强，表明PRRs依赖性抗性的机制可能是这些代谢物信号的去除或对其感知的干扰。该项目将研究拟南芥中生物活性代谢物的细胞外水平在PRR激活后是否会发生变化。深入了解植物防御的这种可能机制，可能会导致转基因作物以更有效和更有针对性的方式部署prr介导的防御。

Bacterial diseases of plants cause significant losses in overall yield and marketability of many economically-important US crops. Although plants possess an immune system that can provide effective resistance against infection, bacteria have evolved sophisticated counter-measures that can effectively suppress these host defenses. As a result, a major determinant of infection outcome is how rapidly both bacteria and host plant can deploy their respective virulence and defense strategies. This project will investigate the molecular basis for chemical signaling events that occur between plants and bacteria at the onset of infection, with a focus on how pathogenic bacteria perceive plant-derived metabolite signals to begin their infection process. Non-specific antimicrobials such as copper sprays and broad-spectrum antibiotics are frequently used to control bacterial diseases in crops. This project will provide a deeper understanding of host perception mechanisms in bacteria that could lead to development of specific chemical inhibitors of this process, thereby providing alternative methods to control disease and potentially improve crop fitness. The project will also provide opportunities for undergraduate students at smaller resource-limited colleges to gain research experience through internships in the investigator's laboratory. Furthermore, a workshop on proteomics methodology will be developed and delivered by the investigator as part of a two-week summer STEM camp for high school students. Genes encoding the virulence-promoting type III secretion system (T3SS) of the plant pathogen Pseudomonas syringae must be expressed at early stages of infection for this bacterium to be fully virulent. In previous work, the investigator identified plant-derived metabolites that induce the expression of T3SS-encoding genes in P. syringae. Although the bioactive plant metabolites are potent enhancers of virulence, how they are perceived by P. syringae to initiate expression of its T3SS is not known. A primary objective of this project is to elucidate the genetic basis for host recognition by P. syringae with a goal of identifying potential receptor proteins that are directly involved in perceiving host metabolite signals. A second objective is elucidate why a P. syringae gacA- mutant that hyper-expresses its T3SS is less virulent, with the goal of understanding how P. syringae coordinates the deployment of virulence factors to maximize pathogenicity. Lastly, exogenous application of T3SS-inducing metabolites during P. syringae infection of Arabidopsis suppresses enhanced resistance mediated by plant pathogen recognition receptors (PRRs), suggesting a mechanism of PRR-dependent resistance may be the removal of these metabolite signals or interference with their perception. This project will investigate if extracellular levels of the bioactive metabolites change following PRR activation in Arabidopsis plants. Insights into this possible mechanism of plant defense may lead to the development of engineered crop plants that deploy PRR-mediated defenses in a more effective and targeted manner.