植物根际促生菌（PGPR）具有促生及生防功能，合理施用含PGPR的生物肥料是实现我国化肥减施、促进农业可持续发展的有效途径。生物肥料中的PGPR施入土壤后须在作物根际有效定殖才能发挥作用，而由根系分泌物介导的PGPR向根表的趋化反应是其有效定殖的重要前提。SQR9是本实验室分离自黄瓜根际并广泛应用的具有促生与生防功能的解淀粉芽孢杆菌，前期研究发现SQR9对黄瓜根系分泌物中的多种小分子有机酸表现出较强趋化性。本研究拟在此基础上继续筛选分泌物中诱导SQR9趋化反应的主要趋化物，并通过突变体/互补菌株趋化实验及等温滴定量热鉴定SQR9中负责感受相应趋化物（含上述小分子有机酸）的受体蛋白，最后通过竞争性抑制结合实验、分析性超速离心、差示量热扫描等生化方法阐明趋化物与受体蛋白之间的互作特征。本研究有助于深入理解PGPR与植物根系互作的分子机制，并为合理开发及施用相应的微生物肥料产品提供理论依据。

Plant growth-promoting rhizobacterias (PGPRs) are a group of bacteria that can promote plant growth and control soil-borne diseases. Application of PGPRs as microbial fertilizers is a promising approach for reducing chemical fertilizer input and promoting the sustainable development of agriculture in China. Effective colonization of the applied PGPRs in rhizosphere is prerequisite for exerting the roles of plant growth promotion and suppression of soil-borne diseases, which is based on the chemotaxis reaction of PGPRs towards plant roots induced by root exudates. This project will focus on the PGPR strain Bacillus amyloliquefaciens SQR9, which was isolated from cucumber rhizosphere by this laboratory and applied widely in agricultural production as the microbial fertilizer. Previous studies showed that SQR9 revealed positive chemotactic response to several small molecular weight organic acids in cucumber root exudates. In this study, more chemotactic attractants of SQR9 in cucumber root exudates will be screened; then chemotactic analysis of mutants/complements and isothermal titration calorimetry (ITC) will be performed for identifying the methyl-accepting chemotaxis proteins (MCPs) in SQR9 for sensing these relevant ligands (including small molecular weight organic acids mentioned above). Finally, this proposal will also illustrate the molecular interaction characteristics between corresponding chemotactic attractant and MCP by competitive inhibition experiments, analytical ultracentrifugation, and differential scanning calorimetry. This study will contribute to understanding of molecular interaction mechanisms between plants and PGPRs, and to provide theoretical instructions for development and application of relevant microbial fertilizer products.