根瘤菌与豆科植物的早期相互识别与应答是成功结瘤的关键步骤之一。MhOpa22是我们从华癸根瘤菌分离鉴定的一种新外膜蛋白，并发现它广泛存在于其它根瘤菌中，其基因突变体不能与宿主植物形成根瘤。但是MhOpa22的作用机制和共生互作途径有待揭示和阐明。本项目拟从MhOpa22的宿主植物互作蛋白受体分离、鉴定及共生表型；MhOpa22对宿主共生及防御基因表达的调制作用；MhOpa22的亚细胞定位和作用途径三个方面开展研究，旨在揭示MhOpa22在共生结瘤中的作用机理和互作途径。预期结果将首次阐明外膜蛋白MhOpa22通过外膜囊泡（Outer Membrane Vesicles, OMVs）介导与豆科植物受体发生相互作用，抑制免疫防御基因表达，从而建立共生关系的作用机制，为该领域提供自主创新研究成果和进展。还可为后续深入及拓展研究根瘤菌外膜蛋白-OMVs-宿主互作及信号传递通路奠定扎实基础。

Early mutual recognition and molecular signaling between rhizobia and leguminous plants is one of the key steps for successful nodulation. In our previous work, MhOpa22 is a new outer membrane protein that was originally isolated and identified from Mesorhizobium huakuii, and we found that it was widely present in other rhizobia as well. The gene mutants could not form root nodules with host plants. However, unknown functional mechanism and rhizobia-legume host symbiotic interactions for MhOpa22 are imperative to be revealed. This project is intended to study the mechanism and rhizobia-host plant interaction of MhOpa22 in the establishment of symbiotic nodulation and will be carried out through the following three aspects, which include the isolation, identification and symbiosis phenotype of MhOpa22 interactive receptor of the host plant, the modulation of MhOpa22 on symbiotic and defensive gene expressions in the host plant, and MhOpa22 protein subcellular localization and action pathway. Therefore, the anticipated results will, for the first time, clarify the functional mechanism of MhOpa22 that mediated through outer membrane vesicles (OMVs) and interaction with leguminous plant cell receptors, inhibiting immune defense genes expressions, and thus establishing a symbiotic relationship. This project will produce achievement and advances with indigenous innovation and intellectual property in this research field. Meanwhile, it is able to provide a new perspective and lay a solid foundation for further study of rhizobia OMVs-delivered membrane proteins-host interactions and a complete signaling pathway in the future.