Center rot of onion is caused by diverse Pantoea species, including P. ananatis, P. agglomerans, P. allii, and P. stewartii ssp. indologenes. While the roles of swimming motility, exopolysaccharide (EPS) production, and quorum sensing (QS) have been explored in P. ananatis in the context of onion disease, those strains were not onion-derived; similar studies in onion-derived Pantoea strains, particularly in P. agglomerans and P. stewartii ssp. indologenes are lacking. In this study, we examined the roles of QS (luxI, luxR), EPS production (epsG), and swimming motility (motB) genes on the virulence of strains from three Pantoea species: P. ananatis PNA 97-1R, P. agglomerans AR1aR, and P. stewartii subsp. indologenes PNA 03-3R, through gene deletions and virulence assays. Mutant characterization confirmed that motB was required for swimming motility, epsG for EPS production, and luxI for acyl-homoserine lactone production in strains from all three Pantoea species. Deletion of motB or epsG did not affect symptom development by any strains, indicating that motility and EPS production were dispensable for onion infection, whereas luxI was essential for virulence in P. ananatis PNA 97-1R and P. stewartii subsp. indologenes PNA 03-3R, but not in P. agglomerans AR1aR, which retained complete virulence despite the luxI deletion. In P. ananatis, while ΔluxI produced no symptoms in onion, ΔluxR and ΔluxIR were virulent, suggesting a regulatory role of luxR as well. These findings indicate that QS-mediated regulation of virulence varies among onion-associated Pantoea strains, whereas motility and EPS production were dispensable for pathogenicity in the strains evaluated.
Lamichhane et al. (Wed,) studied this question.