Is PhoR–PhoP partner fidelity strict? PhoR is required for the activation of the pho regulon in Streptomyces coelicolor

Two-component regulatory systems play a key role in the cell metabolism adaptation to changing nutritional and environmental conditions. The fidelity between the two cognate proteins of a two-component system is important since it determines whether a specific response regulator integrates the signals transmitted by different sensor kinases. Phosphate regulation in Streptomyces coelicolor is mostly mediated by the PhoR–PhoP two-component system. Previous studies elucidated the mechanisms that control phosphate regulation as well as the genes directly regulated by the response regulator PhoP (pho regulon) in this organism. However, the role of the histidine kinase PhoR in Streptomyces coelicolor had not been unveiled so far. In this work, we report the characterization of a non-polar ΔphoR deletion mutant in S. coelicolor that keeps its native promoter. Induction of the phoRP operon was dependent upon phosphorylation of PhoP, but the ΔphoR mutant expressed phoP at a basal level. RT-PCR and reporter luciferase assays demonstrated that PhoR plays a key role in the activation of the pho regulon in this organism. Our results point towards a strict cognate partner specificity in terms of the phosphorylation of PhoP by PhoR thus corroborating the tight interaction between the two-components of this system.