The tomato Pto gene confers resistance to Pseudomonas floridensis, an emergent plant pathogen with just nine type III effectors

A newly discovered bacterial species, Pseudomonas floridensis, has emerged as a pathogen of tomato in Florida. This study compares the virulence and other attributes of P. floridensis to Pseudomonas syringae pv. tomato, which causes bacterial speck disease of tomato. Pseudomonas floridensis reached lower population levels in leaves of tomato as compared to the P. syringae pv. tomato strains DC3000 and NYT1. Analysis of the genome sequence of the P. floridensis type strain GEV388 revealed that it has just nine type III effectors including AvrPtoB(GEV)(388), which is 66% identical to AvrPtoB in DC3000. Five of these effectors have been previously reported to be members of a 'minimal effector repertoire' required for full DC3000 virulence on Nicotiana benthamiana; however, GEV388 grew poorly on leaves of this plant species compared to the DC3000 minimal effector strain. The tomato Pto gene recognizes AvrPtoB in race 0 P. syringae pv. tomato strains, thereby conferring resistance to bacterial speck disease. Pto was also found to confer resistance to P. floridensis, indicating this gene will be useful in the protection of tomato against this newly emerged pathogen.