Physiological and transcriptomic responses associated with melatonin-mediated alleviation of drought injury in maize seedlings

Drought restricts maize establishment by suppressing growth and promoting oxidative damage, while exogenous melatonin has been widely investigated for its potential to alleviate drought stress in plants. However, the concentration-specific physiological and transcriptional responses of maize seedlings to exogenous melatonin remain unclear. Maize seedlings were subjected to normal watering, drought stress, or drought combined with 50 μmol L −1 (M1) or 100 μmol L −1 (M2) melatonin for 7 days. Drought significantly reduced seedling height, stem diameter, and SPAD values, while leaf length showed a numerical decrease; ROS-associated staining and MDA accumulation were also increased. Both melatonin treatments partially alleviated these drought-associated effects, but their response profiles differed: M1 showed the highest mean activities of superoxide dismutase, catalase, and peroxidase, whereas M2 more effectively reduced MDA and maintained SPAD values. Differential expression analysis identified 1232, 320, and 899 differentially expressed genes in the D vs CK, M1 vs D, and M2 vs D comparisons, respectively. Functional analyses associated these genes with redox processes, phenylpropanoid and flavonoid metabolism, cell wall organization, polysaccharide metabolism, and membrane-lipid-related processes. Zm00001eb006180, annotated as ZmEREB180, was prioritized as a drought-responsive candidate gene based on its membership in the WGCNA pink module and its drought-repressed, melatonin-associated recovery pattern. Its overexpression in the maize inbred line B104 was associated with improved shoot and root performance under drought stress. However, because the overexpression experiment used a different genetic background and did not include melatonin treatment, these results do not establish that ZmEREB180 participates in or mediates melatonin-induced drought tolerance. Collectively, exogenous melatonin mitigated drought injury in association with coordinated physiological and transcriptomic responses, which differed between the two tested concentrations.