根瘤菌与宿主植物共生关系的确立是一个复杂的生物学过程，近年来关于宿主对不固氮根瘤菌的宿主制裁引起了广泛地关注，但其中分子的机制尚不清楚；同时发现苜蓿能产生根瘤特异性表达的富含半胱氨酸的小肽（NCRs），能影响根瘤菌在根瘤中类菌体的形成和发育，但关于根瘤菌如何对NCRs产生应答的机制也不清楚。本项目基于前期研究发现苜蓿能对不固氮根瘤菌的类菌体在固氮区的发育产生限制，而NCRs突变植株则不能对不固氮根瘤菌产生宿主制裁，同时根瘤菌中二硫键氧化还原酶基因dsbA缺失后，根瘤不能正常发育，提示该基因可能参与到与NCRs介导的根瘤发育中。本项目拟通过转录组学、遗传学和生化等不同方法对NCRs如何影响不固氮根瘤菌类菌体的发育、根瘤菌中DsbA如何参与到NCRs介导的类菌体发育这两个内容进行研究，以揭示苜蓿中宿主制裁的分子机制和根瘤菌对NCRs进行修饰应答的生物学过程，为共生固氮和根瘤发育提供理论依据。

The establishment of symbiosis system between rhizobia and legume is complex biological process. Recently, it had been found that host plant may limit the growth of non-fixing rhizobia in nodules, which named host sanction. But it has still been unclear the mechanism how host can recognize non-fixing rhizobia and by what kind of method. It had also been found that nodule-specific cysteine-rich peptides (NCRs) may affect bacteriods formation and development in nodules. But how rhizobia respond to NCRs is not clear. We found that host may limit the growth of non-fixing rhizobia in fixing zone when them form nodules on Medicago. And we also found that nodule can not develop correctly when the disulfide oxidoreductase gene (dsbA) in rhizobia was deleted.The results suggest that dsbA may involve in nodule formation mediated by NCRs. The grant will focus on how NCRs affect the bacteriod development of non-fixing rhizobia in fixing zone and how DsbA involes in the bacteriod development mediated by NCRs in Medicago. We will employ the methods of RNA-Seq, molecular biology and Biochemistry to investigate these two main projects. By the grant, we will discover the molecular mechanism of host sanction and how rhizobia resonds to NCRs in Medicago.