Phosphorylation of CorS and CorR, regulatory proteins that modulate production of the phytotoxin coronatine in Pseudomonas syringae

Abstract

Production of the phytotoxin coronatine (COR) in Pseudomonas syringae pv. glycinea PG4180 is controlled by a modified two-component regulatory system consisting of three genes, corR, corP, and corS. CorR and CorP show similarity to response regulators, and CorS is related to histidine protein kinases that function as environmental sensors. In this study, CorR, CorP and the cytoplasmic portion of CorS, designated CorSΔ, were overproduced in P. syringae as translational fusions to the maltose-binding protein and purified by affinity chromatography. Autophosphorylation of CorSΔ was demonstrated when [γ-32P]ATP was used as a phosphodonor. Phosphorylated CorSΔ (CorSΔ∼P) was stable under basic conditions, but extremely sensitive when the pH was reduced, which is consistent with phosphorylation at a histidine residue. CorSΔ∼P transferred its phosphoryl group to CorR but not to CorP, which correlates with the presence of a receiver aspartate residue in the former but not the latter protein. These results indicate that CorS functions as a histidine protein kinase and transphosphorylates CorR, a positive activator of cor gene transcription.