Leafhopper-Induced Activation of the Jasmonic Acid Response Benefits in a Flagellum-Dependent Manner.

Enteric human pathogens such as are typically studied in the context of their animal hosts, but it has become apparent that these bacteria spend a significant portion of their life cycle on plants. survives the numerous stresses common to a plant niche, including defense responses, water and nutrient limitation, and exposure to UV irradiation leading to an increased potential for human disease. In fact, is estimated to cause over one million cases of foodborne illness each year in the United States with 20% of those cases resulting from consumption of contaminated produce. Although successfully persists in the plant environment, phytobacterial infection by or spp. increases survival and infrequently leads to growth on infected plants. The co-association of phytophagous insects, such as the Aster leafhopper, , results in populations that persist at higher levels for longer periods of time when compared to plants treated with alone. We hypothesized that leafhoppers increase persistence by altering the plant defense response to the benefit of the bacteria. Leafhopper infestation activated the jasmonic acid (JA) defense response while colonization triggered the salicylic acid (SA) response. In tomato plants co-treated with and leafhoppers, both JA- and SA-inducible genes were activated, suggesting that the presence of leafhoppers may affect the crosstalk that occurs between the two immune response pathways. To rule out the possibility that leafhoppers provide additional benefits to , plants were treated with a chemical JA analog to activate the immune response in the absence of leafhoppers. Although bacterial populations continue to decline over time, analog treatment significantly increased bacterial persistence on the leaf surface. Bacterial mutant analysis determined that the bacterial flagellum, whether functional or not, was required for increased survival after analog treatment. By investigating the interaction between this human pathogen, a common phytophagous insect, and their plant host, we hope to elucidate the mechanisms promoting survival on plants and provide information to be used in the development of new food safety intervention strategies.