DnaJ, a heat shock protein 40 family member, is essential for the survival and virulence of plant pathogenic Pseudomonas cichorii JBC1

Bacterial plant pathogens must cope with various environmental conditions and defenses from their hosts for colonization and infection. Heat shock proteins (HSPs) play critical roles in a variety of cellular processes, such as the maintenance of cellular homeostasis in response to environmental stress. However, the significance of HSP40 family protein DnaJ in virulence of plant pathogenic bacteria has not yet been explored. To elucidate the function of DnaJ in Pseudomonas cichorii JBC1 (PcJBC1) virulence, we generated dnaJ-deficient (JBC1^ΔdnaJ) mutant using CRISPR-CAS9. The disease severity by JBC1^ΔdnaJ was significantly reduced compared with wild-type (WT) and dnaJ-complemented (JBC1^ΔdnaJ + pdnaJ) strain. The defect of DnaJ suppressed siderophore production, extracellular DNA (eDNA) release, biofilm formation, and swarming motility and made the strain sensitive to stresses such as heat and H₂O₂. The supplementation of eDNA recovered the amount of biofilm formation by JBC1^ΔdnaJ. Our results indicate that DnaJ is a key player in the survival and colonization of bacterial plant pathogens on plant surfaces as well as bacterial responses to abiotic and biotic stresses, which are determinative to cause disease. These findings can broaden our understanding of plant and bacterial pathogen interactions.