RDO3 REPRESSOR 27, a new MED25 allele, regulates seed dormancy dependent on DOG1 and ABA pathways in Arabidopsis

The Thr445Met substitution in the novel allele med25-5 uncouples seed dormancy from flowering, and MED25 acts as a negative regulator of seed dormancy via the DOG1 and ABA pathways. MED25, a pivotal subunit of the Mediator complex, regulates diverse biological processes, but its role in seed dormancy remains unclear. Here, we identified a novel MED25 allele, med25-5, harboring a Thr445Met substitution in the MD domain, which enhances seed dormancy without affecting flowering time in Arabidopsis thaliana. The med25-5 mutant exhibited increased dormancy with altered expressions in DOG1 and ABA signaling genes (e.g., ABI1, NHL6) and increased sensitivity to ABA and PAC. Either dog1-3 or abi3-10 can completely repress the enhanced seed dormancy of med25, indicating MED25 regulates dormancy requiring the DOG1 and ABA pathways. The Thr445 residue is conserved across crops, highlighting MED25's potential for crop improvement against pre-harvest sprouting. Our study uncovers MED25 as a negative regulator of seed dormancy, providing insights into the molecular mechanisms coordinating dormancy and flowering.