Redox-Dependent Chaperoning of GBF1 Condensates Regulates Seed Germination in Arabidopsis.

Reactive oxygen species (ROS) are pivotal signals that trigger the transition from seed dormancy to germination, yet the molecular link between ROS and transcriptional regulation has remained unclear. Here, we uncover a redox-dependent mechanism focusing on the transcription factor G-box binding factor 1 (GBF1) and its chaperone GBF1-interacting protein 1 (GIP1). We show that GBF1 undergoes liquid-liquid phase separation (LLPS) to form condensates that enhance target DNA binding and repress the transcription of the germination-promoting gene Cathepsin B-like protease 3 (CathB3). Both the prion-like domain and the bZIP dimerization domain are indispensable for GBF1 condensation and DNA binding. GIP1 colocalizes with GBF1 and functions as a molecular chaperone that fine-tunes condensate size and liquidity, thereby enhancing GBF1's DNA-binding and repressive capacity. Oxidation of GIP1 by ROS burst during germination abolishes its chaperone activity, leading to aberrant, less dynamic GBF1 condensates and consequent derepression of CathB3, which promotes germination. This work identifies a ROS-sensitive chaperone-condensate axis as a key molecular gatekeeper of seed germination, revealing how redox signals are translated into developmental decisions through the material properties of transcriptional condensates.