Changes to the leaf surface environment in response to human pathogen Salmonella enterica serovar Typhimurium 14028s

Outbreaks of food-borne diseases has been increasingly linked to plant-based products, as human pathogens can utilize plants as transmission vectors. The human pathogen Salmonella enterica serovar Typhimurium 14028s (hereafter STm 14028s) can persist on and within the leaf for extended periods of time but does not cause disease on the plant. This study aims to understand how STm 14028s alters the leaf surface environment, also known as the phylloplane, during its interaction with the plant. In this work, I show how STm 14028s changes the metabolites accumulated on the leaf surface. I provide evidence that the alteration of metabolites is unique to STm 14028s through comparison to the plant pathogen Pseudomonas syringae pv. tomato DC3000 (hereafter Pst DC3000). In addition, this study is the first to describe the mechanism STm 14028s utilizes to overcome stomatal immunity. I highlight the role of auxin in the mechanism deployed by STm 14028s by demonstrating that both plant- and microbe-derived auxin contribute to STm 14028s’s stomatal reopening. I show that the the Arabidopsis auxin signaling pathway is manipulated by STm 14028s to cause stomatal reopening. Finally, I characterize the JAZ family in lettuce to create Lsjaz4 mutant lines that will hopefully be more resistant to human pathogens. Overall, this study illustrates that STm 14028s causes unique changes to the leaf surface environment to promote its survival on a non-host.