Direct receptor competition gates RGL2 proteolysis for seed germination timing in Arabidopsis.

Seed germination is orchestrated by antagonistic gibberellin (GA) and abscisic acid (ABA) signals converging on the master germination repressor RGL2. Here, we unveil a receptor-competition paradigm where ABA receptors (PYLs) stabilize RGL2, both through direct physical interaction and through functional sequestration of DWA1, the CUL4-DDB1 E3 ligase substrate adapter mediating RGL2 ubiquitination. GA receptors (GID1s) counteract this stabilization by competitively displacing PYLs from RGL2, leveraging their superior binding capacity to license DWA1-mediated degradation. Crucially, this competition is defined by the concentration of abscisic acid and gibberellin as they regulate PYL and GID1 expression. Genetic epistasis confirms that PYLs act upstream of DWA1, competing directly with GID1 at RGL2. This receptor-occupied switch converts environmental fluctuations into proteolytic decisions: transient stress imposes a reversible "pause state" through PYL dominance, while sustained GA biosynthesis permits germination via GID1-mediated degradation. Our work establishes direct receptor competition as a complementary layer to hormone crosstalk, providing a universal framework for signal-driven developmental transitions.