Differential regulation of Salmonella typhimurium genes involved in O-antigen capsule production and their role in persistence within tomato fruit

Enteric pathogens, including non-typhoidal Salmonella spp. and enterovirulent Escherichia coli, are capable of persisting and multiplying within plants. Yet, little is still known about the mechanisms of these interactions. This study identified the Salmonella yihT gene (involved in synthesis of the O-antigen capsule) as contributing to persistence in immature tomato fruit. Deletion of yihT reduced competitive fitness of S. enterica sv. Typhimurium in green (but not ripe, regardless of color) tomato fruit by approximately 3 logs. The yihT recombinase-based in vivo expression technology (RIVET) reporter was strongly activated in unripe tomato fruit, and fitness of the mutant inversely correlated with the level of the yihT gene expression. Expression of yihT in mature tomato fruit was low, and yihT did not affect competitive fitness within mature fruit. To better understand the molecular basis of the phenotype, behaviors of the yihT RIVET reporter and the yihT mutant were tested in tomato fruit defective in ethylene signaling. These experiments suggest a role for functional ethylene-mediated signaling in the persistence of Salmonella spp. within tomato fruit. Furthermore, jasmonic acid and its precursors strongly reduced expression of yihT.