Exogenous Melatonin Inhibits the Expression of GmABI5 and Enhances Drought Resistance in Fodder Soybean Through an ABA-Independent Pathway.

Drought is a pivotal abiotic stress that hampers plant growth and development; however, melatonin has emerged as a crucial regulator in mitigating plant responses to such drought-induced stress. By subjecting the plants to drought conditions and applying exogenous melatonin, we found that melatonin significantly improves the drought tolerance of fodder soybean. Remarkably, both stomatal examination and hormone analysis point to a substantial reduction in the endogenous ABA levels following melatonin treatment. Transcriptome analysis revealed significant enrichment of differentially expressed genes in the ABA signalling pathway. The pivotal transcription factor GmABI5 was successfully identified and cloned, with the application of exogenous melatonin notably decreasing the expression of GmABI5. Furthermore, the OE-GmABI5 lines exhibited notably retarded growth, accompanied by a rise in ABA content and an upsurge in the expression of ABA-dependent genes. Contrarily, melatonin treatment led to a complete reversal of these traits in the OE-lines. This study provides new insights and methods for enhancing drought resistance in crops and offers a fresh perspective on the interrelationships between hormones in plants under drought stress.