Exogenous MgH₂-derived hydrogen alleviates cadmium toxicity through m⁶A RNA methylation in rice

Cadmium (Cd) contamination poses a substantial threat to crop yields and human health. While magnesium hydride (MgH₂) has been reported as a hydrogen (H₂) donor that promotes plant growth under heavy metal contamination, its role in rice remains elusive. Herein, seedlings of Oryza sativa L. Japonica variety Zhonghua 11 (ZH11) were selected and exposed to 20 µL of 1-mol/L cadmium chloride (CdCl₂) solution via hydroponics to simulate Cd stress. Meanwhile, 0.1 mg of MgH₂ was used to slow-release H₂ to the experimental group to explore its potential effects on rice over a 2-week period. The results indicated that Cd exposure severely inhibited the growth and development of ZH11 rice seedlings. However, the exogenous slow-release of H₂ from MgH₂ effectively mitigated this inhibitory effect by restoring the balance of reactive oxygen species (ROS), maintaining endogenous H₂ homeostasis, and supporting the photosynthetic system. High-performance liquid chromatography analysis revealed that exogenous H₂ reduces m⁶A RNA methylation levels in mRNA under Cd stress. Consequently, MeRIP-seq was conducted to investigate the effect of Cd exposure in rice in the presence and absence of H₂. The m⁶A modifications were enriched at the start codon, stop codon, and 3' UTR. By integrating RNA-seq data, 118 transcripts were identified as differentially methylated and expressed genes under Cd stress. These gene annotations were associated with ROS, biological stress, and hormonal responses. Notably, 297 differentially methylated and expressed genes were identified under Cd stress in the presence of H₂, linked to heavy metals, protein kinases, and calcium signaling regulation. Cd strongly activates the MAPK pathway in response to stress. Exogenous H₂ reduces Cd accumulation as well as enhances plant tolerance and homeostasis by lowering m⁶A levels, thereby decreasing the mRNA stability of these genes. Our findings indicate that MgH₂, by supplying H₂, regulates gene expression through m⁶A RNA methylation and confers Cd tolerance in rice. This study provides potential candidate genes for studying the remediation of heavy metal pollution in plants.