Plant-cell-wall-degrading enzymes (PCWDEs) of Pectobacterium carotovorum subsp. carotovorum are the key virulence factor in pathogenesis of soft rot disease of vegetables. The production of PCWDEs is controlled in a cell density dependent manner to avoid the premature production of PCWDEs and subsequent activation of plant defense. N-oxoacyl-homoserine lactone (OHL) is essential for quorum sensing in the soft rot pathogen and the expI gene is responsible for OHL production. The ExpI homolog isolated from P. carotovorum subsp. carotovorum SL940 had 94% identity with ExpI of E. carotovora subsp. carotovora scc3193 and 74% identity with CarI of E. carotovora subsp. atroseptica. The transgenic plants that express expI uner the control of CaMV35S promoter were able to produce diffusible OHL. Transgenic plants producing OHL were very resistant to the infection of P. carotovorum subsp. carotovorum. Since the PR1 gene was strongly induced and NPR1 and NPR4 were induced weakly in transgenic plants compared to the wild type, salicylic acid-dependent pathways is likely involved in the resistance to the soft rot pathogen P. carotovorum subsp. carotovorum in ExpI transgenic plants.