WRKY transcription factors play essential roles during leaf senescence. However, the mechanisms by which they regulate this process remains largely unknown. Here, we identified the transcription factor WRKY75 as a positive regulator during leaf senescence. Mutations of WRKY75 caused a delay in age-triggered leaf senescence, whereas overexpression of WRKY75 markedly accelerated this process. Expression of senescence-associated genes ( SAG s) was suppressed in WRKY75 mutants but increased in WRKY75 -overexpressing plants. Further analysis demonstrated that WRKY75 directly associates with the promoters of SAG12 and SAG29 , to activate their expression. Conversely, GAI and RGL1, two DELLA proteins, can suppress the WRKY75-mediated activation, thereby attenuating SAG expression during leaf senescence. Genetic analyses showed that GAI gain-of-function or RGL1 overexpression can partially rescue the accelerated senescence phenotype caused by WRKY75 overexpression. Furthermore, WRKY75 can positively regulate WRKY45 expression during leaf senescence. Our data thus imply that WRKY75 may positively modulate age-triggered leaf senescence through the gibberellin-mediated signaling pathway.
Endogenous and exogenous signals are perceived and integrated by plants to precisely control defense responses. As a crucial environmental cue, light reportedly plays vital roles in plant defenses against necrotrophic pathogens. Phytochrome-interacting factor (PIF) is one of the important transcription factors which plays essential roles in photoreceptor-mediated light response. In this study, we revealed that PIFs negatively regulate plant defenses against Botrytis cinerea. Gene expression analyses showed that the expression level of a subset of defense-response genes was higher in pifq (pif1/3/4/5) mutants than in the wild-type control, but was lower in PIF-overexpressing plants. Chromatin immunoprecipitation assays proved that PIF4/5 binds directly to the ETHYLENE RESPONSE FACTOR1 (ERF1) promoter. Moreover, genetic analyses indicated that the overexpression of ERF1 dramatically rescues the susceptibility of PIF4-HA and PIF5-GFP transgenic plants, and that PIF controls the resistance to B. cinerea in a COI1- and EIN2-dependent manner. Our results provide compelling evidence that PIF, together with the jasmonate/ethylene pathway, is important for plant resistance to B. cinerea.
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