光合根瘤菌和植物的互作共生，对粮食生产和生态保护具有重要意义，然而其之间的互作分子机制仍然不清楚。我们的前期研究表明，光合根瘤菌ORS278的群体感应系统对菌株与水稻的互作共生有着决定性影响。群体感应系统敲除后，共生有益的菌株转而对水稻致病，说明群体感应系统调控着光合根瘤菌与水稻共生的关键互作因子。本项目拟以野生型菌株作为参照系，对群体感应系统敲除菌株进行转座子突变筛选和高通量测序，筛选影响与植物互作的基因，并通过代谢组学分析查找影响互作的代谢产物，从而揭示光合根瘤菌对植物的共生与致病的转换机制。明确影响共生与致病的关键互作因子和调控机理，将有助于构建重组菌株，提高菌株和植物的互作效率，对保障粮食安全，促进生态建设具有理论意义和实际应用价值。

Photosynthetic rhizobium can develop symbiotic association with host plant, which plays vital role in the crop production and ecological protection. However, the symbiotic molecular mechanism is not determined yet. Here our preliminary result showed that the quorum-sensing deletion mutant of Bradyrhizobium sp. ORS278 turns into a pathogen against the rice plants, suggesting that the quorum-sensing system plays a role in mediating the symbiotic process. With the WT and the pathogenic mutant strains, we plan to conduct transposon library screening combined with high through sequencing to look for the symbiotic and pathogenic candidate genes, and to identify the metabolites secreted by bacteria using the metabolomics analysis, in order to uncover the mechanism of pathogenic transition. Understanding the key factors affecting symbiotic and pathogenic transition and related regulatory mechanisms, may benefit construction of recombinant photosynthetic strains for increasing symbiotic efficiency, which may have significant theoretical and applied value for food security and ecological conservation.