The Symbiotic Function And Protein Interaction Of Effector Protein NopP In Mesorhizobium Huakuii7653R

The leguminous plants can establish a symbiosis "nodule" structure with rhizobia, which is involved in a complex process including gene expression and regulation, signal perception and transduction, interactions of molecules between rhizobia and host plants. Type III secretion effector protein NopP of rhizobia plays an important role in the above process.In our previous work, we have identified an protein NIP43in Astragalus sinicus which interacts with NopP of Mesorhizobium huakuii7653R. Their interactions have been confirmed through bimolecular fluorescence complement (BiFC) technique in the tobacco cells. This study aims to verify the symbiotic function of NopP in7653R and protein-protein interactions with NIP43. The results can be summarized as follows:Firstly, it is found that Mesorhizobium loti MAFF303099can also estabilish symbiosis with Astragalus sinicus, but displaying weak phenotypes compared to7653R with much fewer nodules and lower nitrogen fixation ability. With the transferring of7653R nopP into MAFF303099, it is found that exogenious nopP gene plays no remarkable effects on the symbiotic phenotypes in Lotus japonicus, comparing to MAFF303099itself. On the other hand, it showed that7653R cannot nodulate on plant of Lotus japonicus.Secondly, the interactions between three NopP homologous proteins in Rhizobium sp NGR234, Bradyrhizobium japonicum USDA6and Rhizobium fredii USDA257with NIP43have been examined respectively. It is found that NopP homologous protein from B. japonicum USDA6can interact with NIP43.Thirdly, this study constructed a nopP inactivation mutant strain7653R-nopPmut through a gene specific-site insertion method. Pot experiment and symbiotic phenotypes examinations showed the nodule numbers and biomass of host plant induced by the Mh-nopPmut decreased, but the nodule nitrogen fixation activity showed no significant difference, when compared with the wild-type7653R.The above results provide additional evidence to further confirm that the interactions between the effector protein NopP and host protein NIP43, also the symbiotic function phenptyes of nopP gene in7653R were determined. The work has laid a good basis for the deeper investigation of functional mechanisms of effector proteins NopP in nodulation in the future.