UC San Diego

Food security is a function of, among other factors, plant health. Because people subsist on a small number of key crops in many parts of the world, disease epidemics among such crops can have dire ramifications. It therefore behooves us to learn more about the plant immune system in order to better protect crops and safeguard the food supply. Many studies on plant immunity have focused in on the role of phytohormones, particularly salicylic acid (SA), jasmonic acid (JA), and ethylene (ET), in negotiating defense strategies against pathogens with different lifestyles. Our work addresses the role of AtERF13, an Arabidopsis ethylene response factor previously found to enhance abscisic acid (ABA)-mediated responses to abiotic stress. We found in proteome profiling of plant immune signaling that S168- phosphorylated ERF13 increases concurrent with early effector-triggered immunity mediated by the R protein RPM1. Using quantitative luminescence assays to measure the growth of bioluminescent bacteria in planta, we determined that overexpression of ERF13 induces susceptibility to the bacterial pathogen Pseudomonas syringae. We also found that ERF13 overexpression promotes chlorosis and inhibits plant growth. Semi-quantitative RT- PCR analysis furthermore demonstrated that ERF13 stimulates the expression of PDF1.2a, a JA/ET-inducible pathogenesis-related gene. We conclude that ERF13 lies at a junction in the signaling pathways of SA, JA, ET, and ABA, and that it promotes susceptibility to P. syringae by negotiating the crosstalk between these hormones which shapes and tailors the plant defense response