吲哚乙酸合成关键基因ysnE增强促生菌SQR9根际定殖的分子机制研究

施用含有植物根际促生菌的生物肥料是推动农业可持续发展的重要途径，阐明促生菌的根际定殖机制可为提高肥料产品的应用效果提供理论依据。目前有关根际促生菌自身趋化、成膜等方面定殖机制的研究已比较成熟，但对其通过强化局部根际互作而提高自身定殖方面的理解还非常欠缺。实验室前期发现促生菌SQR9吲哚乙酸合成（主要促生机制）关键基因突变体∆ysnE在黄瓜根表的定殖能力显著弱于野生型，且该差异是由野生型SQR9调控局部根系分泌物组分改变进而强化菌-植根际互作引起的。本项目首先将在分根系统中鉴定同一黄瓜植株根系两侧分别接种野生型SQR9与∆ysnE后，其局部根系分泌物差异组分中影响菌株定殖的关键物质；随后探索关键物质调控菌株定殖的分子机制；最后在上述机制的基础上建立强化菌株SQR9根际定殖和功能发挥的调控技术。预期本研究将深入对促生菌根际定殖机制的理解，同时为增强促生菌根际定殖和生物肥料应用效果提供理论指导。

Application of plant growth-promoting rhizobacteria as bio-fertilizers is an important strategy for promoting the sustainable development of agriculture in China; understanding of the rhizosphere colonization mechanism by rhizosphere beneficial microbes can provide theoretical foundation for improving the application effects of the relevant bio-fertilizer products. Currently, involvement of chemotaxis and biofilm formation by plant growth-promoting rhizobacteria in rhizosphere colonization has been well studied; however, understanding of enhancing local rhizosphere interactions and colonization by plant growth-promoting rhizobacteria themselves is much limited. This laboratory has construct a ∆ysnE mutant that deficient in synthesis of indole-3-acetic acid (the main ability contributes to plant growth-promotion by the bacteria), based on a plant growth-promoting rhizobacteria SQR9; colonization of ∆ysnE on cucumber roots was significantly impaired as compared with the wide type in single inoculation, mixed-inoculation, and split-root systems; it was also assessed that this colonization difference was attributed to the SQR9-mediated reshaping of local root exudates composition, followed by enhancement of the plant-microbe interactions. Based on this finding, the key compounds from the variational root exudates composition in response to strain SQR9 and ∆ysnE inoculation, which can also modulate SQR9 colonization, will be firstly identified in a split-root system. After that, the molecular biology mechanism involved in the mediation of bacterial colonization by these key compounds will be investigated. Finally, the regulation technique for enhancing rhizosphere colonization and function exertion by strain SQR9 will be developed, based on the colonization-mediation mechanism raised above. This study will contribute to deepening the knowledge of the rhizosphere colonization mechanism by plant growth-promoting rhizobacteria, and provide theoretical instructions for improving the colonization of plant growth-promoting rhizobacteria, as well as agricultural application effects of relevant bio-fertilizer products.