Previous interaction with phytopathogenic bacteria alters the response of Arabidopsis against Tetranychus urticae herbivory

ABSTRACT Plant response to individual biotic stresses depends on its physiological state when the challenge is perceived. Optimal conditions for infestation of the spider mite Tetranychus urticae are associated with high temperatures and scarce precipitation. Here, we analyze the impact of previous interactions with the hemibiotrophic bacteria Pseudomonas syringae pv. tomato DC3000 or the necrotroph Dickeya dadantii 3937 on Arabidopsis thaliana plants under mite optimal conditions. Our results showed that both bacterial strains inoculated at adverse low humidity conditions induced the expression of JA-related genes in the plant even when disease symptoms are not observed. This effect was more evident when heat-inactivated bacteria were used, but a significant reduction in mite leaf damage was only detected when plants were previously inoculated with the heat-inactivated hemibiotroph bacteria. These results indicate that bacterial interaction compromises the plant response to subsequent herbivore stress, even under suboptimal conditions for bacterial multiplication.