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

植物病原体对粮食、纤维、生物燃料和美容作物的生产造成负面影响。浸水是由病原真菌、卵菌和细菌引起的疾病的一个标志症状，它是受感染的植物组织细胞外空间积聚的液体。植物病原体还必须从受感染的宿主组织中获得营养。尽管它们在发病机制中起着核心作用，但对于感染微生物如何诱导水浸泡和获得营养缺乏机械解释。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一种单一的关键毒力因子来诱导浸水。在玉米中，积累的液体中也含有丰富的支持病原菌增殖的营养物质，这表明水分和养分获得的关键过程之间存在着相互关系。这些发现以及对毒力因子胞内寄主靶标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分和营养物质的分子机制。对病程中这一关键步骤的基础知识的获得将反过来为培育抗病植物和开发抗病植物提供生物技术途径。由于关键的毒力因子在不同的植物病原细菌中广泛保守，这些策略将从番茄和玉米扩展到许多农业上重要的植物。目前的猜测认为，病原体诱导的水分和营养物质释放到细胞外空间是由于对植物细胞的破坏。然而，初步数据表明，紫丁香假单胞菌是一种新的细菌。番茄(PST)和潘托亚种(Pantoea stewartii subsp.)Stewartii(Pnss)部署Avre家族III型效应蛋白，在破坏受感染植物细胞的完整性之前，诱导水浸泡并增加细胞外营养代谢物的丰度。此外，PNSS的致病性依赖于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。现有的和新产生的缺乏Avre家族效应靶标的突变植物，包括质膜定位的磷酸酶、质膜跨越受体样激酶和HCAA生物合成酶，将揭示这些宿主靶标在完整植物细胞外的效应诱导水分和营养积累中的贡献。将野生型植物的质膜蛋白质组与不完全支持Avre家族毒力活性的突变体进行比较，将有助于识别与这些效应器诱导的寄主生理扰动有关的蛋白磷酸化或丰度的变化。这些生理学、代谢学、蛋白质组学和遗传学分析将揭示Avre家族效应器调节水分和营养物质穿过寄主细胞质膜的机制，并将这些机制置于Pst和Pnss分别在双子叶和单子叶寄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宿主中诱导浸水和营养的细胞外空间的理解。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.