Light-dependent activation of TCP4 by the GATA25 transcription factor promotes petiole and hypocotyl elongation in Arabidopsis thaliana

Plants coordinate cell elongation with the daily light/dark cycle, an important adaptive strategy for optimizing growth under changing environmental conditions. However, the transcriptional mechanisms linking light signals to plant developmental growth remain poorly understood. In this study, we identified the GATA25 transcription factor as a regulator of petiole and hypocotyl elongation in response to light and photoperiod. Overexpression of GATA25 in Arabidopsis thaliana increased petiole and hypocotyl lengths and elevated TCP4 transcript levels. We demonstrated that GATA25 directly binds to the promoter of TCP4 and activates its transcription using transcriptional activation analysis, a glucocorticoid receptor-based inducible system, chromatin immunoprecipitation, and electrophoretic mobility shift assays. Furthermore, yeast two-hybrid assay and bimolecular fluorescence complementation analyses showed that GATA25 physically interacts with the E3 ubiquitin ligase COP1. Notably, overexpression of GATA25 did not increase TCP4 transcript levels in dark conditions, suggesting that GATA25 activity is suppressed in dark conditions. Based on these findings, we propose a model in which GATA25 is destabilized by COP1 in dark conditions, restricting TCP4 activation to the light conditions. Taken together, these findings provide a framework for understanding how the daily light/dark cycle regulates cell elongation in a photoperiod-dependent manner through the GATA25-TCP4 module.