Construction and assignment of symbiotic phenotypes of outer membrane porin encoding gene MCHK_1326 in Mesorhizobium huakuii 7653R

Abstract:

[Objective] The gene MCHK_1326 from Mesorhizobium huakuii 7653R encoding an outer membrane porins may be involved in the process of rhizobial infection, nodulation and symbiotic nitrogen fixation. This study was aimed to explore the function of this gene in legume-rhizobium symbiosis. [Methods] Bioinformatics analysis used to study the structural characteristics and biological functions of MCHK_1326 protein. The spatial and temporal expression characteristics of MCHK_1326 gene was assayed by histochemical staining. The deletion mutant strain (7653R△1326 strain) was constructed by the Cre-loxp system. Early infection events and symbiotic phenotype of wild-type and mutant strain were observed. The symbiotic phenotype of the mutant strain was also measured under the conditions of adding nitrogen source. [Results] The gene MCHK_1326 was highly expressed during the entire early phase of infection and in the infection zone of mature nodules, such as the elongation process of the infected thread. The infection threads and the number of nodules primordium by the mutant were significantly reduced; compared with the controls, the plants inoculated with 7653RΔ1326 strain displayed significant reduction in the fresh weight of the aerial plant, nitrogenase activity, and the amount and weight of nodules of 7653Δ1326 strain was significantly lower. The defected symbiotic phenotype of plants inoculated with 7653RΔ1326 strain could be restored to normal by adding inorganic nitrogen source. [Conclusion] The gene MCHK_1326 participates in the early infection and nodulation processes and plays an important role in the development of nodule and symbiotic nitrogen fixation.