|Li Xue Liu, Qin Qin Li, Yun Zeng Zhang, Yue Hu, Wen Xin Chen and Chang Fu Tian. The nitrate-reduction gene cluster components exertlineage-dependent contributions to optimization of Sinorhizobium symbiosis with soybeans. Environmental Microbiology. DOI|
The nitrate-reduction gene cluster components exertlineage-dependent contributions to optimization of Sinorhizobium symbiosis with soybeans
Li Xue Liu, Qin Qin Li, Yun Zeng Zhang, Yue Hu,Jian Jiao, Hui Juan Guo, Xing Xing Zhang,Biliang Zhang, Wen Xin Chen and Chang Fu Tian
Receiving nodulation and nitrogen fixation genesdoes not guarantee rhizobia an effective symbiosiswith legumes. Here, variations in gene content weredetermined for three Sinorhizobium species showingcontrasting symbiotic efficiency on soybeans. Anitrate-reduction gene cluster absent in S. sojae wasfound to be essential for symbiotic adaptations of S. fredii and S. sp. III. In S. fredii, the deletion mutationof the nap (nitrate reductase), instead of nir (nitritereductase) and nor (nitric oxide reductase), led todefects in nitrogen-fixation (Fix–). By contrast, noneof these core nitrate-reduction genes were requiredfor the symbiosis of S. sp. III. However, within thesame gene cluster, the deletion of hemN1 (encodingoxygen-independent coproporphyrinogen III oxidase)in both S. frediiand S. sp. III led to the formation ofnitrogen-fixing (Fix+) but ineffective (Eff–) nodules.These Fix1/Eff– nodules were characterized bysignificantly lower enzyme activity of glutamine synthetaseindicating rhizobial modulation of nitrogenassimilationby plants. A distant homologue ofHemN1 from S. sojae can complement this defect in S. fredii and S. sp. III, but exhibited a more pleotropicrole in symbiosis establishment. These findingshighlighted the lineage-dependent optimization ofsymbiotic functions in different rhizobial speciesassociated with the same host.