Transcriptome Analysis Reveals the Molecular Mechanisms Through Which Exogenous Methyl Jasmonate Enhances Mercury Stress Tolerance in Maize Seedlings

Mercury (Hg) pollution has led to a serious decline in crop yields. Methyl jasmonate (MJ), as a plant hormone, regulates plant responses to heavy metal stress. Nonetheless, the pathways by which MJ modulates Hg tolerance in plants are still not well elucidated. Our study aimed to elucidate the positive impacts of MJ in alleviating Hg-induced toxicity in maize (Zea mays L.) seedlings using an integrated approach combining physiological assessments and transcriptomic analysis. The findings indicated that exogenous MJ mitigated Hg-induced inhibition of photosynthetic performance by up-regulating photosynthesis-related and light-harvesting-related genes and increasing chlorophyll content. Under Hg stress, MJ enhances proline accumulation in maize seedlings by up-regulating essential genes in the proline biosynthesis pathway and down-regulating critical genes in the proline degradation pathway. MJ also elevates the expression of key enzymes involved in phenylpropanoid biosynthesis in maize seedlings, decreases malondialdehyde (MDA) content, and enhances root vitality. In addition, MJ may exert a detoxification effect on maize seedlings under Hg stress by regulating the expression of various genes linked to basic nutrient transport proteins, as well as those involved in the transport, influx, and distribution of metal ions. These findings indicate that MJ is essential for enhancing plant tolerance to Hg stress, thereby establishing a theoretical framework for the advancement and utilization of environmentally friendly agricultural methods involving plant hormones.