The Overexpression of an EnvZ-like Protein Improves the Symbiotic Performance of Mesorhizobia

The two-component signal transduction system EnvZ/OmpR is described to mediate response to osmotic stress, although it regulates genes involved in other processes such as virulence, fatty acid uptake, exopolysaccharide production, peptide transportation, and flagella production. Considering that some of these processes are known to be important for a successful symbiosis, the present study addresses the effects of extra envZ-like gene copies in the Mesorhizobium–chickpea symbiosis. Five Mesorhizobium-transformed strains, expressing the envZ-like gene from M. mediterraneum UPM-Ca36T, were evaluated in terms of symbiotic performance. Chickpea plants inoculated with envZ-transformed strains (PMI6envZ+ and EE7envZ+) showed a significantly higher symbiotic effectiveness as compared to the corresponding control. In plants inoculated with PMI6envZ+, a higher number of infection threads was observed, and nodules were visible 4 days earlier. Overall, our results showed that the overexpression of Env-like protein may influence the symbiotic process at different stages, leading to strain-dependent effects. This study contributes to elucidating the role of an EnvZ-like protein in the rhizobia–legume symbioses.