Emergence of the Dickeya genus involved duplication of the OmpF porin and the adaptation of the EnvZ-OmpR signaling network.

Dickeya species cause various diseases in a wide range of crops and ornamental plants. Understanding the molecular program that allows the bacterium to colonize the plant is key to developing new pest control methods. Unlike other enterobacterial pathogens, Dickeya dadantii, the causal agent of soft rot disease, does not require the EnvZ-OmpR system for virulence. Here, we showed that during the emergence of the genus Dickeya, the gene encoding the porin OmpF was duplicated and that the expression of ompF2 was deleterious for virulence. We revealed that while the EnvZ-OmpR system was activated in vitro by acidic pH and even though the pH was acidic when the plant is colonized, this system was repressed by phenolic acid (generated by the plant's defenses). These results provide a unique- biologically relevant-perspective on the consequence of gene duplication and the adaptive nature of regulatory networks to retain the duplicated gene.