Biological Role of Motility in the Plant Pathogenic Bacterium Ralstonia Solanacearum

大多数与植物相关的细菌可以移动，尽管移动会消耗大量能量，并可能引起宿主的防御反应。众所周知，移动的能力有助于细菌对动物致病，但细菌运动在植物发病机制中的作用在很大程度上未被探索。植物病原体Ralstonia solanacearum的两个特征良好的非运动突变体在实际的土壤入侵毒力试验中对番茄造成的疾病显著减少，表明该性状确实有助于毒力。该项目的目标是结合遗传学、组织病理学和生态学方法，全面描述这种与植物相关的细菌的生活史中的运动作用。第一个目标是确定运动如何促进机体健康。研究人员将在显微镜下检查感染了荧光运动细菌或非运动细菌的番茄根，以比较这些菌株在发病早期的行为。这些实验将验证运动在宿主入侵和殖民早期起关键作用的假设。为了验证疾病发展后期的运动性是积极不利的假设，研究人员将测量一个始终处于运动性的调节突变的毒力。因为运动性也可能影响植物外的细菌适应性，他们将比较运动性菌株和非运动性菌株的土壤存活率，以验证运动性增加腐生菌在土壤和腐烂植物材料中的存活率的假设。第二个目的是将细菌运动的影响从鞭毛本身的影响中分离出来，因为鞭毛可以介导附着在植物表面并被宿主识别。为了确定鞭毛是否将细菌附着在植物表面，研究人员将比较无鞭毛和有鞭毛但瘫痪的突变体对番茄根部的附着。分析植物的生化反应和防御基因表达将揭示寄主植物是否识别纯化的茄青霉鞭毛或其成分鞭毛蛋白。第三个目的是探索龙舌兰如何调节其运动性。这一特性可能是由一个复杂的层次结构控制的，包括内部响应鞭毛调节子、已知的毒力因子调节子和寄主植物信号。研究人员将使用报告基因融合和调控突变体来定义该物种的运动基因调控。由于番茄红霉在培养中的运动并不能反映病原菌在其自然栖息地的行为，因此将在植物中进行基因表达研究。总的来说，这里提出的实验将产生对移动能力如何在其复杂的生命周期中帮助或可能阻碍这种细菌的综合理解。

Most plant-associated bacteria can move, even though motility uses much energy and may elicit host defense responses. The ability to move is known to help bacteria pathogenic to animals, but the role of bacterial motility in plant pathogenesis is largely unexplored. Two well-characterized nonmotile mutants of the plant pathogen, Ralstonia solanacearum, caused significantly less disease on tomato in a realistic soil invasion virulence assay, showing that this trait does contribute to virulence. The goal of this project is to combine genetic, histopathological, and ecological approaches to comprehensively describe the role of motility in the life history of this plant-associated bacterium. The first objective is to determine how motility contributes to organismal fitness. The investigators will microscopically examine tomato roots infected with fluorescent motile or nonmotile bacteria to compare the behavior of these strains during the early stages of pathogenesis. These experiments will test the hypothesis that motility plays a key role early in host invasion and colonization. To test the hypothesis that motility late in disease development is actively disadvantageous, the investigators will measure the virulence of a regulatory mutant that is always motile. Because motility is likely to affect bacterial fitness outside the plant as well, they will compare soil survival of motile and nonmotile strains to test the hypothesis that motility increases saprophytic survival in soil and decaying plant material. The second objective is to separate the effects of bacterial movement from those of the flagella themselves, because flagella may mediate attachment to plant surfaces and recognition by the host. To determine if flagella attach bacteria to plant surfaces, investigators will compare attachment of non-flagellated and flagellated but paralyzed mutants to tomato roots. Analysis of plant biochemical responses and defense gene expression will reveal whether host plants recognize purified R. solanacearum flagella or their component flagellins. The third objective is to explore how R. solanacearum regulates its motility. This trait is likely controlled by a complex hierarchy involving an internally responsive flagellar regulon, known virulence factor regulators, and host plant signals. Investigators will use reporter gene fusions and regulatory mutants to define motility gene regulation in this species. Because R. solanacearum motility in culture does not reflect the behavior of the pathogen in its natural habitat, gene expression studies will be conducted in planta. Collectively, the experiments proposed here will yield an integrated understanding of how the ability to move helps, and possibly hinders, this bacterium throughout its complex life cycle.