GIGANTEA mediates WRKY-dependent transcriptional activation of leaf senescence

Leaf senescence is a genetically programmed process that integrates developmental and environmental cues to optimize nutrient remobilization. GIGANTEA (GI), a circadian regulator with diverse functions in flowering, temperature, and stress response pathways, has also emerged as a positive regulator of age-dependent leaf senescence. However, the molecular link between the GI and senescence-associated transcription factors is still poorly defined. Here, we investigated the interactions between GI and WRKY transcription factors from the WRKY family, which have been previously reported as positive regulators of senescence in Arabidopsis. GI physically interacts with WRKY45 and WRKY75 transcription factors in a yeast-II-hybrid assay. We further analyzed the interaction between WRKY75 and GI in vivo using co-immunoprecipitation (Co-IP) assay in a transient expression system in Nicotiana benthamiana. Genetic analyses using Arabidopsis mutant lines further revealed that GI is required for the WRKY75-mediated promotion of age-dependent leaf senescence. Consistent with these phenotypes, WRKY75 positively regulates SAG12 expression during senescence in a GI-dependent manner. Together, our findings position GI as an integrative component of WRKY-driven senescence pathways, expanding its functional role in coordinating age-dependent leaf senescence.