ClpA affects the virulence of on melon by regulating RepA.

ClpA is a widely conserved protease in bacteria that plays a key role in virulence. To investigate its specific mechanism of action in the pathogenicity of (formerly , we constructed a deletion mutant, Δ. The Δ mutant of displayed reduced virulence on melon seedlings, and reduced motility, swarming ability, and antioxidant capacity. On the other hand, the deletion of mutant reduced the resistance to elevated temperature and enhanced biofilm formation ability. Using qRT-PCR, we observed that negatively regulates the expression of the virulence-related genes , , , and , while positively regulating , , and . Bacterial double hybrid and Glutathione-S-transferase pulldown (GST-pulldown) results showed that ClpA interacts directly with RepA, and negatively regulates the expression of . After deletion of the gene, the pathogenicity of was lost, biofilm formation ability was enhanced, and the expression of , , and was positively regulated. These results indicate that ClpA plays a key role in the regulation of several virulence traits of , paving the way for future studies to better elucidate the virulence mechanisms of this bacterial plant pathogen.