Jasmonate (JA) and ethylene (ET) are two major plant hormones that synergistically regulate plant development and tolerance to necrotrophic fungi. Both JA and ET induce the expression of several pathogenesis-related genes, while blocking either signaling pathway abolishes the induction of these genes by JA and ET alone or in combination. However, the molecular basis of JA/ET coaction and signaling interdependency is largely unknown. Here, we report that two Arabidopsis ET-stabilized transcription factors (EIN3 and EIL1) integrate ET and JA signaling in the regulation of gene expression, root development, and necrotrophic pathogen defense. Further studies reveal that JA enhances the transcriptional activity of EIN3/EIL1 by removal of JA-Zim domain (JAZ) proteins, which physically interact with and repress EIN3/EIL1. In addition, we find that JAZ proteins recruit an RPD3-type histone deacetylase (HDA6) as a corepressor that modulates histone acetylation, represses EIN3/EIL1-dependent transcription, and inhibits JA signaling. Our studies identify EIN3/EIL1 as a key integration node whose activation requires both JA and ET signaling, and illustrate transcriptional derepression as a common mechanism to integrate diverse signaling pathways in the regulation of plant development and defense.root hair | Botrytis cinerea P lants are sessile organisms and face different environmental changes during their lifespan. To survive various abiotic and biotic stresses, plants synthesize a number of small molecules functioning as phytohormones to elaborately regulate their growth, development, and defense. Two types of phytohormonesethylene (ET) and jasmonate (JA)-are crucial for plant development and defense against necrotrophic fungi infections (1-3). Complicated modes of interaction between ET and JA have been documented in different processes. For example, ET strongly suppresses JA-induced wounding-responsive gene expression, but JA suppresses ET-induced apical hook formation (4, 5), indicative of their antagonisms. Upon necrotrophic fungi infections, plants can quickly produce ET and JA and induce the expression of downstream defense genes (like ERF1, ORA59, and PDF1.2) that help plants tolerate or fight against the fungal pathogens (1). Plants treated with exogenous JA or ET express high levels of defense genes (6, 7), and simultaneous treatment with JA and ET results in the highest expression (8). Nevertheless, in the ET or JA insensitive mutant (ein2 or coi1, respectively), JA and ET alone or in combination fail to induce the expression of those defense genes (8, 9), indicating that the two hormone-signaling pathways are required concomitantly for the activation of plant-defense response. These results suggest that JA and ET act synergistically and mutually dependently in regulating necrotrophic pathogen responses. However, the molecular details underlying such hormone synergy and signaling interdependency are currently unknown.ET is a gaseous hormone, which is perceived by its receptors and represses a Raf-like kinase CON...