No abstract

Necrotrophic fungi cause devastating diseases in both horticultural and agronomic crops, but our understanding of plant defense responses against these pathogens is still limited. In this study, we demonstrated that AtWRKY75 positively regulates the jasmonate (JA)-mediated plant defense against necrotrophic fungal pathogens Botrytis cinerea and Alternaria brassicicola and also affects plants’ sensitivity to JA-inhibited seed germination and root growth. Quantitative RT-PCR analysis indicated that the expression of several JA-associated genes, such as ORA59 and PDF1.2, was significantly reduced in wrky75 mutants and significantly enhanced in 35S:WRKY75 transgenic plants. Immunoprecipitation assays revealed that WRKY75 directly binds to ORA59 promoters and represses its transcription. In vivo and in vitro experiments suggested that WRKY75 interacts with several JASMONATE ZIM-domain proteins, which are repressors of the JA signaling pathway. We determined that JAZ8 represses the transcriptional function of WRKY75, thereby attenuating the expression of its regulon. Consistent with this finding, overexpression of JAZ8 repressed plant defense response to B. cinerea. Taken together, our study provides evidence that WRKY75 functions as a critical component of the JA-mediated signaling pathway to positively regulate Arabidopsis defense response to necrotrophic pathogens.