Regulation of Pseudomonas syringae Virulence by Plant-Derived Chemical Signals

植物的细菌性病害导致美国许多经济上重要的作物的总产量和销售能力的显著损失。虽然植物具有免疫系统，可以提供有效的抵抗感染，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防御。因此，感染结果的主要决定因素是细菌和宿主植物能够多快地部署其各自的毒力和防御策略。该项目将研究在感染开始时发生在植物和细菌之间的化学信号事件的分子基础，重点是病原菌如何感知植物来源的代谢物信号以开始其感染过程。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中宿主感知机制的更深入了解，这可能导致这一过程的特定化学抑制剂的开发，从而提供控制疾病的替代方法，并可能提高作物适应性。该项目还将为资源有限的较小学院的本科生提供机会，通过在调查员实验室实习获得研究经验。此外，研究人员将开发并提供蛋白质组学方法研讨会，作为为期两周的高中生STEM夏令营的一部分。编码植物病原体假单胞菌的促毒III型分泌系统（T3SS）的基因必须在感染的早期阶段表达，以使该细菌完全有毒。在以前的工作中，研究人员确定了诱导P. pastingae中T3SS编码基因表达的植物衍生代谢物。虽然生物活性植物代谢物是有效的毒力增强剂，但它们如何被P.lingae感知以启动其T3SS的表达尚不清楚。该项目的主要目的是阐明宿主识别的遗传基础，目的是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P.lingae gacA突变体毒性较低，目的是理解P.lingae如何协调毒力因子的部署以使致病性最大化。最后，外源应用T3SS诱导的代谢产物在P. dichloringae感染拟南芥抑制增强的抗性介导的植物病原体识别受体（PRRs），这表明PRRs依赖性抗性的机制可能是这些代谢物信号的去除或干扰其感知。本项目将研究拟南芥中PRR激活后，细胞外生物活性代谢物水平是否发生变化。深入了解这种可能的植物防御机制可能会导致工程作物的发展，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.