Leaf senescence can be triggered and promoted by various environmental stressors, developmental cues, and endogenous hormone signals. Several lines of evidence have suggested the involvement of WRKY transcription factors in regulating leaf senescence, but the underlying mechanisms and signaling pathways involved remain elusive. In this study, we identified Arabidopsis thaliana WRKY DNA-binding protein 45 (WRKY45) as a positive regulator of age-triggered leaf senescence. Loss of WRKY45 function resulted in increased leaf longevity in age-triggered senescence, whereas overexpression of WRKY45 significantly accelerated age-triggered leaf senescence. Consistently, expression of SENESCENCE-ASSOCIATED GENEs (SAGs) was significantly reduced in wrky45 mutants but markedly enhanced in transgenic plants overexpressing WRKY45. Chromatin immunoprecipitation assays revealed that WRKY45 directly binds the promoters of several SAGs such as SAG12, SAG13, SAG113, and SEN4. Both in vivo and in vitro biochemical analyses demonstrated that WRKY45 interacts with the DELLA protein RGA-LIKE1 (RGL1), a repressor of the gibberellin (GA) signaling pathway. We found that RGL1 repressed the transcription activation function of WRKY45, thereby attenuating the expression of its regulon. Consistent with this finding, overexpression of RGL1 resulted in significantly increased leaf longevity in age-triggered senescence. Taken together, our results provide compelling evidence that WRKY45 functions as a critical component of the GA-mediated signaling pathway to positively regulate age-triggered leaf senescence.

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.