Transcriptomic analysis of melatonin-mediated drought stress response genes in alfalfa during germination period

Drought stress is a predominant abiotic factor contributing to reduced crop yields globally. Therefore, exploring the molecular mechanism of drought control is of great significance to improve drought resistance and ultimately achieve crop yield increase. As a plant endogenous hormone, melatonin plays a key role in the regulation of abiotic stress, but the key genes and metabolic pathways of melatonin mediated drought resistance regulation in alfalfa have not been fully revealed. Based on transcriptomics and physiological index detection, this study aimed to explore the regulatory mechanism of melatonin in alleviating drought stress during alfalfa germination.

The findings revealed that alfalfa seedlings treated with melatonin exhibited higher germination rates, increased shoot length, and greater fresh weight compared to those exposed solely to drought stress. Additionally, there was a reduction in the levels of malondialdehyde (MDA) and superoxide anion (O₂^-), while the activity and concentration of superoxide dismutase (SOD), peroxidase (POD), and glutathione (GSH) were enhanced to varying extents. To investigate the molecular mechanism underlying melatonin-mediated drought resistance in alfalfa, we performed a transcriptomic analysis on the seedlings. In the drought treatment group, we identified a total of 1,991 differentially expressed genes (DEGs), comprising 778 up-regulated and 1,213 down-regulated genes. Conversely, in the melatonin-treated group, we discovered 2,336 DEGs, including 882 up-regulated and 1,454 down-regulated genes.

Through the application of GO functional annotation and KEGG pathway enrichment analysis, we discovered that DEGs were predominantly enriched in pathways related to flavonoid and isoflavone biosynthesis, plant hormone biosynthesis and signal transduction, glutathione metabolism, and MAPK signaling, and the ABC transporter signaling. Notably, the DEGs added to the MT group showed greater enrichment in these pathways. This suggests that MT mitigates drought stress by modulating the expression of genes associated with energy supply and antioxidant capacity. These findings hold significant reference value for breeding drought-tolerant alfalfa and other crops.