The global virulence regulator PhcA negatively controls the Ralstonia solanacearum hrp regulatory cascade by repressing expression of the PrhIR signaling proteins.

PhcA positively and negatively regulates many genes responsible for pathogenicity of Ralstonia solanacearum. The type III secretion system-encoding hrp regulon is one of the negatively controlled operons. PhcA bound to the promoter region of prhIR and repressed its expression, demonstrating that PhcA shuts down the most upstream component of a signal transfer system for hrpB activation.