Specificity of chemotaxis-driven motility in Sinorhizobium meliloti host interaction

趋化性使可移动的细菌能够远离有害化学物质，转向有益的化学物质。一种独特的可移动的土壤细菌是根瘤菌，它可以在土壤中自由生活，并与豌豆、大豆和紫花苜蓿等豆科植物建立特定的共生关系。这种共生为寄主植物提供氮素，这是植物生长最有限的养分。在模式根瘤菌Sinorhizobium Meliloti中的趋化过程允许有机体识别其宿主，从而改善了共生关系，从而促进了植物的生长。PI在苜蓿中发现了多个不同的化学感受器，这些化学感受器用于感觉化合物。然而，关于根瘤菌化学受体的吸引谱或特异性还知之甚少。这个项目的首要目标是描述苜蓿趋化受体对寄主来源的引诱剂范围的特定适应。这项研究的结果将通过发现豆类与根瘤菌相互作用的新特性来改变我们目前对土壤中细菌行为的概念。土壤细菌紫花中华根瘤菌的趋化性是其与紫花苜蓿建立共生关系的重要前提。一种新型细菌趋化性的发现，即对植物携带的甜菜碱的吸引，以及对这些化合物的根瘤化学受体的鉴定，扩大了我们对植物-细菌交流的理解。这项研究的结果将为开发新的和创新的策略来增强共生菌的化学感受开辟道路，这将提高共生效率，导致更高的固氮水平，并最终可能增加作物产量。该项目可以通过减少化肥的使用，直接惠及未来的农业和环境问题。更广泛的影响活动将涉及研究生的跨学科培训。该团队致力于指导研究生和本科生，特别是代表不足的少数族裔和女性。公共推广活动包括为小学生和高中生在校园内外进行动手演示，以及让高中生参与研究。作为一个模型系统，研究人员的目标是阐明控制豆科植物-根瘤菌通讯的分子机制。了解这些机制可以为解决令人望而生畏的农业和环境问题开辟新的重要途径。这项研究将对功能缺乏了解的苜蓿化学感受器进行表征。在一个正交法中，研究人员将定义植物衍生化合物的性质，这些化合物负责将紫花苜蓿招募到宿主根际。植物分泌到根际的化合物的组成已经特别进化，以吸引共生微生物到它们相应的宿主的根。首先，研究人员建议使用质谱学代谢组分析和定量趋化性分析来表征紫花苜蓿宿主紫花苜蓿分泌的各种植物化学物质。这项研究将揭示苜蓿引诱组，并确定单个化合物对趋化作用的贡献。其次，他们建议确定单个化学受体的受体配体，并通过行为、遗传、生化和结构分析确定受体与配体的相互作用。McpX已经非常先进的生化和结构表征为这些分析提供了蓝图。这项拟议的研究将促进我们对植物和微生物之间对话中渗出物的作用的了解。该项目由分子和细胞生物科学(CDF集群)和综合组织系统(PBI集群)联合资助，并由理事会的生命规则风险基金提供额外支持。该奖项反映了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。

Chemotaxis enables motile bacteria to move away from harmful and towards beneficial chemicals. One unique group of motile soil bacteria are rhizobia, which can live freely in the soil, as well as engage in specific symbiotic relationships with leguminous plants such as peas, soy beans, and alfalfa. This symbiosis supplies the host plant with nitrogen, which is the most limiting nutrient for plant growth. The process of chemotaxis in the model rhizobium Sinorhizobium meliloti allows the organism to recognize its host, which improves the symbiotic relationship, and consequently, enhances plant growth. The PI discovered multiple and diverse chemoreceptors in S. meliloti, which are used to sense chemical compounds. However, little is known about the attractant spectrum or the specificity of rhizobial chemoreceptors. The overarching goal of this project is to characterize the specific adaptations of S. meliloti chemoreception to the range of host-derived attractants. Results from this research will transform our current concepts of bacterial behavior in soil through discovery of emergent properties of legume-rhizobia interactions. Chemotaxis of the soil bacterium Sinorhizobium meliloti is a critical prerequisite for the establishment of its symbiotic relationship with alfalfa. The discovery of a new type of bacterial chemotaxis, namely attraction to plant-borne betaines, and the identification of the rhizobial chemoreceptor for these compounds expands our understanding of plant-bacteria communication. The results of this research will open avenues for developing novel and innovative strategies to enhance chemoreception in the symbiotic bacterium S. meliloti, which will increase symbiotic efficiency, result in higher level of nitrogen fixation, and may ultimately increase crop yields. This project can directly benefit future agricultural and environmental issues by reducing the use of chemical fertilizers. Broader Impacts activities will involve the interdisciplinary training of graduate students. The team is committed to mentoring graduate and undergraduate students, especially underrepresented minorities and women. Public outreach activities include hands-on demonstrations for elementary and high school students, both on- and off-campus, and involvement of high school students in research.Using the Alfalfa-S. meliloti interaction as a model system, the investigators aim to elucidate the molecular mechanisms that govern legume-rhizobia communications. Understanding these mechanisms could open important new avenues for addressing daunting agricultural and environmental issues. This research will characterize S. meliloti chemoreceptors for which functional understanding is lacking. In an orthogonal approach, the investigators will define the nature of plant-derived compounds responsible for the recruitment of S. meliloti to the host rhizosphere. The composition of compounds exuded by plants into the rhizosphere has specifically evolved to attract symbiotic microbes to the roots of their corresponding hosts. First, the investigators propose to characterize the diverse phytochemicals secreted by the S. meliloti host alfalfa using mass-spectrometric metabolome analysis and quantitative chemotaxis assays. This study will uncover the S. meliloti attractome and establish the contributions of individual compounds to chemotaxis. Second, they propose to identify receptor ligands for individual chemoreceptors and determine receptor-ligand interaction through behavioral, genetic, biochemical, and structural analyses. The already highly advanced biochemical and structural characterization of McpX serves as blueprint for these analyses. The proposed research will advance our knowledge of the role of exuded root metabolites in the dialogue between plants and microbes.The Project is jointly funded by Molecular and Cellular Biosciences (CDF Cluster) and Integrative Organismal Systems (PBI Cluster), with additional support provided by the Directorate's Rule of Life Venture Fund.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.