The CmGLK-CmCHLH module regulates seed germination rate via the abscisic acid pathway in melon

The uniformity and speed of seedling emergence are particularly important in vegetable industrial seedlings. A higher germination rate can shorten the seedling cycle and increase seedling uniformity in melon (Cucumis melo L.). However, the molecular mechanisms underlying the regulation of seed germination in melon remain largely unknown. Golden2-like (CmGLK) has been identified as a key transcription factor involved in chloroplast development, and we found that it also plays a role in regulating seed germination rate in melon. The near-isogenic line of Cmglk (Cmglk-NIL) and CmGLK knockout mutants in melon exhibited slower seed germination rates than those in wild-type lines, while the overexpression of CmGLK in tomato (Solanum lycopersicum L.) showed significantly increased germination rates. Comparative transcriptome analysis revealed that numerous abscisic acid (ABA)-related genes were involved in seed germination. Furthermore, the Cmglk-NIL and CmGLK knockout mutants exhibited increased sensitivity to exogenous ABA during seed germination, while the CmGLK overexpression lines in tomato showed reduced sensitivity to ABA. Bioinformatics analysis and experimental validation indicated that CmGLK could directly bind to the promoter of the H SUBUNIT OF MG-CHELATASE (CmCHLH) gene, thereby activating its expression. Functional validation via CmCHLH overexpression in tomato resulted in a significantly increased seed germination rate, demonstrating its positive regulatory role in germination. These findings identify a CmGLK-CmCHLH regulatory module that regulates seed germination rate through the ABA pathway in melon. They also enhance our understanding of the mechanisms underlying melon seed germination and provide a reference for seed germination regulation in other crops.