Real Time Chemotaxis in Commensal Plant-microbe Associations

各种植物-微生物和微生物-微生物的相互作用发生在根际，其结果影响植物的健康和生产力。细菌和寄主植物之间的分子交流，允许建立特定的共生或致病植物-细菌相互作用的细节是已知的。然而，在根际中占主导地位的共生植物-微生物关联尚未得到相同程度的研究，并且关于共生土壤细菌启动与植物根表面松散关联的策略或这些关联的时空动态的了解相对较少。本研究旨在实时描述与共生细菌-植物关联建立和维持相关的关键细菌决定因素，以及这些关联的时空动态。实验将表征巴西氮螺旋菌与小麦根系结合过程中的传感和趋化作用，这是在高时空分辨率尺度上定量分析植物-微生物有益共生关系的良好模型。通过实验和数学模型之间的迭代，该研究将描述多种趋化途径为细菌感知和响应与其在土壤和根际生活方式相关的梯度的能力提供的选择优势。接下来，将确定能够整合代谢状态和传感的受体在介导根际定植中的作用。该项目还将使用一种新的表达系统来跟踪细胞内关键代谢物（c-di-GMP）浓度的变化如何实时影响运动行为。最后，将实施一种定量方法来实时监测共生植物根定殖的时空动态中的传感和趋化作用。大多数土壤细菌与植物的根形成共生关系，这些细菌的测序基因组编码至少两个Che途径。获得的结果将直接转座到其他可移动的土壤细菌，并将为建立共生植物-微生物关联所涉及的分子机制提供急需的定量见解。这些知识是对存在于根际的多种植物-微生物关系的系统级理解的先决条件。对共生植物-微生物关联进行实时和定量监测的方法将首次记录这些关联的时空动态，并最终为未来操纵根际以改善植物健康和生产力的有效策略提供信息。更广泛的影响：该项目将为定量分析植物-微生物关联的时空动态提供新的工具和方法，包括实时跟踪根-微生物关联的方法。从这项研究中得出的数学模型将在未来系统级模拟根际调控和促进植物健康的植物-微生物关系中发挥重要作用。该项目还将描述将增强合成生物学工具包的传感模块。此外，将为研究生和本科生，包括科学中代表性不足的群体的成员，建立生物学和数学的跨学科互动。

Various plant-microbe and microbe-microbe interactions take place in the rhizosphere, the outcomes of which influence plant health and productivity. The molecular communication between bacteria and host plants that allow the establishment of specific symbiotic or pathogenic plant-bacteria interactions are known in detail. However, commensal plant-microbe associations that dominate in the rhizosphere have not been studied to the same extent and relatively little is known regarding the strategies used by commensal soil bacteria to initiate a loose association with plant root surfaces or the spatiotemporal dynamics of these associations. This research aims to characterize key bacterial determinants implicated in the establishment and maintenance of commensal bacteria-plant associations and the spatiotemporal dynamics of these associations, in real-time. Experiments will characterize the role of sensing and chemotaxis in the association of Azospirillum brasilense with wheat roots, which is an excellent model to quantitatively analyze beneficial commensal plant-microbe associations at high temporal and spatial resolution scales. Using iterations between experiments and mathematical modeling, the research will characterize the selective advantage that multiple chemotaxis pathways provide to the ability of bacteria to sense and respond to gradients relevant to their lifestyle in the soil and in the rhizosphere. Next, the role of receptors capable of integrating metabolic status with sensing in mediating rhizosphere colonization will be determined. The project will also use a novel expression system to track how changes in the intracellular concentration of a key metabolite (c-di-GMP) affect locomotor behaviors in real time. Last, a quantitative approach to monitor, in real-time, the role of sensing and chemotaxis in the spatiotemporal dynamics of commensal plant-root colonization will be implemented. Most soil bacteria form commensal associations with the roots of plants and the sequenced genomes of these bacteria encode at least two Che pathways. Results obtained will be directly transposable to other motile soil bacteria and will provide much needed quantitative insights into the molecular mechanisms involved in the establishment of commensal plant-microbe associations. This knowledge is a prerequisite to a systems-level understanding of the diverse plant-microbe associations that exist in the rhizosphere. The approach to real-time and quantitative monitoring of commensal plant-microbe associations will document the spatiotemporal dynamics of these associations for the first time and ultimately inform future effective strategies to manipulate the rhizosphere to improve plant health and productivity. Broader Impacts: This project will provide new tools and methods to quantitatively analyze the spatiotemporal dynamics of plant-microbe associations, including approaches to track real-time root-microbe associations. The mathematical model derived from this research will be useful in future systems-level simulations of plant-microbe associations for rhizosphere manipulation and promotion of plant health. The project will also characterize sensory modules that will enhance the synthetic biology toolkit. In addition, cross-disciplinary interactions in biology and mathematics for graduate students and undergraduate students, including members of underrepresented groups in the sciences, will be established.