Effects of Hormone Crosstalk on Endophytic Bacterial Communities

Abstract

The plant hormones salicylic and jasmonic acid (SA and JA, respectively) both play a crucial role in the induction of plant defense system pathways and long-term pathogen resistance. Plants, which do not have an active cellular immune system like animals, instead rely on the release of specific molecules to mediate defense. In general, the SA pathway is activated by biotrophic pathogens and primarily induces antimicrobial responses, while JA is activated by necrotrophic pathogens and herbivory, and induces separate chemical responses. SA and JA are reciprocally antagonistic: activation of one pathway inhibits activation of the other. Here we explore how SA-JA inhibitory crosstalk is used by pathogens or herbivores to combat plant defense. We study the effects of hormone crosstalk on bacterial growth in two plant models: Cardamine cordifolia and Arabidopsis thaliana, which we treated to induce defense pathways. These plants were inoculated with endophytic bacteria isolated from field C. cordifolia plants, and the effects of hormone treatment on bacterial growth rates were measured. We show that JA-induced defenses, which are commonly associated with necrotrophic pathogens, affect varied biotrophic Pseudomonas strains both positively and negatively. Notably, we show that JA-induce defenses affect wild P. fluorescens strains more negatively than SA-defenses.