Transcription Factor WRKY75 Interacts with DELLA Proteins to Affect Flowering

Abstract

Flowering time is tightly controlled by both endogenous and exogenous signals. Although several lines of evidence have suggested the involvement of WRKY transcription factors in floral initiation, the underlying mechanisms and signaling pathways involved remain elusive. Here, we newly identified Arabidopsis (<i>Arabidopsis thaliana</i>) WRKY DNA binding protein75 (WRKY75) as a positive regulator of flowering initiation. Mutation of <i>WRKY75</i> resulted in a delay in flowering, whereas overexpression of <i>WRKY75</i> significantly accelerated flowering in Arabidopsis. Gene expression analysis showed that the transcript abundance of the flowering time integrator gene <i>FLOWERING LOCUS T</i> (<i>FT</i>) was lower in <i>wrky75</i> mutants than in the wild type, but greater in <i>WRKY75</i>-overexpressing plants. Chromatin immunoprecipitation assays revealed that WRKY75 directly binds to the promoter of <i>FT</i> Both in vivo and in vitro biochemical analyses demonstrated that WRKY75 interacts with DELLA proteins. We found that both REPRESSOR OF <i>ga1-3</i> (RGA) RGA-LIKE1 (RGL1) and GA INSENSITIVE (GAI) can repress the activation ability of WRKY75, thereby attenuating expression of its regulon. Genetic analyses indicated that <i>WRKY75</i> positively regulates flowering in a FT-dependent manner and overexpression of <i>RGL1</i> or gain-of-function of <i>GAI</i> could partially rescue the early flowering phenotype of <i>WRKY75</i>-overexpressing plants. Taken together, our results demonstrate that WRKY75 may function as a new component of the GA-mediated signaling pathway to positively regulate flowering in Arabidopsis.