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.
Keywords: DELLA protein; WRKY transcription factor; gibberellin; senescence.
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