Mechanisms linking nutrient acquisition and water-soaking during bacterial infection of plants

植物病原体对食品、纤维、生物燃料和美学作物的生产产生负面影响。浸水是指受感染植物组织的细胞外空间中液体的积聚，是由致病真菌、卵菌和细菌引起的疾病的标志性症状。植物病原体也必须从被感染的宿主组织中获取营养。尽管它们在发病机制中起着核心作用，但关于感染微生物如何诱导水浸泡和获取营养的机制解释尚缺乏。在番茄、模式植物拟南芥和玉米中引起细菌性斑点病的细菌病原体依赖于单一的关键毒力因子来诱导水浸泡。在玉米中，积累的液体也富含支持病原体增殖的营养物质，这表明在水分和营养获取的关键过程中存在相互关系。这些发现以及对毒力因子的细胞内宿主靶点的鉴定，使拟议的研究能够阐明从受感染的植物组织中释放水和营养物质的分子机制。在发病机制中这一关键步骤的基础知识的获得将反过来使育种和开发抗病植物的生物技术方法成为可能。由于关键的毒力因子在不同的植物致病菌中广泛保守，这些策略将从番茄和玉米扩展到许多重要的农业植物。普遍的推测认为，病原体诱导的水和营养物质释放到细胞外空间是植物细胞受损的结果。然而，初步数据表明，丁香假单胞菌pv。番茄（Pst）和泛菜（Pantoea stewartii subsp）。Stewartii （Pnss）利用avre家族III型效应蛋白诱导水浸泡，并在破坏受感染植物细胞完整性之前增加细胞外营养代谢物的丰度。此外，Pnss的致病性取决于avre家族效应物诱导的宿主苯丙素代谢的扰动，包括羟基肉桂酸酰胺（HCAAs）的积累。现有的和新产生的突变植物缺乏avre家族效应靶点，包括质膜定位磷酸酶、质膜跨越受体样激酶和HCAA生物合成酶，将揭示这些宿主靶点对效应诱导的完整植物细胞外水分和营养积累的贡献。将野生型植物的质膜（磷酸化）蛋白质组与不完全支持avre家族效应物毒力活性的突变体进行比较，将有助于鉴定与这些效应物诱导的宿主生理扰动遗传相关的蛋白质磷酸化或丰度变化。这些生理学、代谢组学、蛋白质组学和遗传学分析将揭示avre家族效应物调节宿主细胞质膜上水分和营养物质运动的机制，并将这些机制置于Pst和Pnss分别在双子叶和单子叶宿主中产生的疾病状态的背景下。更广泛地说，这些发现将促进对植物病原体如何在其宿主体内诱导水浸泡和营养的细胞外空间的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Plant pathogens negatively affect production of food, fiber, biofuel and aesthetic crops. Water-soaking, which is the accumulation of fluid in extracellular spaces of infected plant tissues, is a hallmark symptom of diseases caused by pathogenic fungi, oomycetes and bacteria. Plant pathogens must also obtain nutrients from infected host tissues. Despite their central roles in pathogenesis, mechanistic explanations for how infecting microbes induce water-soaking and acquire nutrients are lacking. Bacterial pathogens that causes bacterial speck disease in tomato, the model plant Arabidopsis, and maize rely on a single, key virulence factor to induce water-soaking. In maize, the accumulating fluids are also rich in nutrients that support pathogen proliferation, indicating an inter-relationship in the key processes of water and nutrient acquisition. These findings along with identification of intracellular host targets of the virulence factor enable the proposed studies to elucidate molecular mechanisms underlying the liberation of water and nutrients from infected plant tissues. The acquired fundamental knowledge of this key step in pathogenesis will in turn enable breeding and biotechnological approaches for development of disease resistant plants. Because the key virulence factor is broadly conserved among diverse plant-pathogenic bacteria, these strategies will extend beyond tomato and maize to a multitude of agriculturally important plants.Prevailing speculation posits that pathogen-induced release of water and nutrients into extracellular spaces results from damage to plant cells. However, preliminary data indicate that Pseudomonas syringae pv. tomato (Pst) and Pantoea stewartii subsp. Stewartii (Pnss) deploy AvrE-family type III effector proteins that induce water-soaking and increase the extracellular abundance of nutritive metabolites prior to disrupting the integrity of infected plant cells. Additionally, pathogenicity of Pnss depends on AvrE-family effector induced perturbation of host phenylpropanoid metabolism, including accumulation of hydroxycinammic acid amides (HCAAs). Existing and newly generated mutant plants lacking AvrE-family effector targets, including plasma membrane-localized phosphatases, plasma membrane-spanning receptor-like kinases, and HCAA biosynthetic enzymes, will reveal the contribution of these host targets to effector-induced water and nutrient accumulation outside of intact plant cells. Comparisons of the plasma membrane (phospho)proteomes of wild-type plants with mutants that do not fully support the virulence activity of the AvrE-family effectors will enable identification of changes in protein phosphorylation or abundance that are genetically linked to these effector-induced perturbations of host physiology. These physiological, metabolomic, proteomic and genetic analyses will reveal mechanisms through which AvrE-family effectors regulate the movement of water and nutrients across the plasma membrane of host cells and place these mechanisms in the context of the disease state produced by Pst and Pnss in their dicot and monocot hosts, respectively. More generally, the findings will advance understanding of how plant pathogens induce water-soaked and nutritive extracellular spaces in their hosts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.