Analysis of virulence mechanisms of plant pathogens is often limited by the lack of genetic tools that can be used to identify genes that are preferentially expressed during their interactions with plants. In the present study, we used the newly constructed IVET (in vivo expression technique) plasmid pIviGK and the corresponding antibiotic resistance-based selection method to identify genes that encode pathogenicity factors of the soft rot-causing bacterium Pseudomonas viridiflava. These included pel, the gene encoding pectate lyase, which is responsible for the development of soft rot symptoms. We have also isolated and characterized the gene mviN(pv) encoding a putative novel membrane associated virulence factor of P. viridiflava. A mutation in mviN(pv) was shown to influence motility as well as virulence of P. viridiflava. The mviN(pv) gene is expressed to a moderate level in LB media and its expression increases under inducing conditions as was shown by measuring in planta expression dynamics of the fused gfp reporter gene.