GmFIP37, a core m6A methyltransferase in soybean (Glycine max), confers salt and drought tolerance via synergistic regulation of m6A modification and antioxidant-osmolyte homeostasis.

RNA N6-methyladenosine (m6A) modification, the most abundant epigenetic modification in eukaryotic mRNAs, regulates gene expression via modulating mRNA translation, degradation, and other post-transcriptional processes, and is critical for plant growth, development, and abiotic stress responses. Soybean (Glycine max), a globally vital food and oil crop, suffers severe yield and quality losses under salt and drought stresses; however, the functions of m6A regulatory genes, especially methyltransferases, in soybean abiotic stress responses remain largely uncharacterized. In this study, four GmFIP37 genes were identified in the soybean genome. Bioinformatic analyses revealed that GmFIP37 proteins have conserved physicochemical properties, harbor the core WTAP functional domain, and their promoters contain abundant abiotic stress-responsive cis-acting elements. Expression pattern analysis showed GmFIP37 are ubiquitously expressed across soybean tissues (with the highest expression in stems and roots) and are rapidly induced under salt and PEG (drought-mimic) stresses. Subcellular localization assays confirmed GmFIP37 localizes to the nucleus. Functional validation demonstrated that heterologous expression of GmFIP37c in the yeast Saccharomyces cerevisiae strain INVSc1 significantly enhanced yeast tolerance to salt and drought stresses. Overexpression of GmFIP37c in soybean hairy root composite plants increased total root m6A content, improved growth traits (e.g., root length, root surface area, plant height), and enhanced salt tolerance via increasing antioxidant enzyme (SOD, POD) activities and osmolyte (proline, betaine) contents while reducing reactive oxygen species (ROS) accumulation. Conversely, virus-induced gene silencing (VIGS) of GmFIP37c in soybean reduced salt and drought tolerance. Additionally, heterologous overexpression of GmFIP37c in Arabidopsis thaliana promoted seedling growth and improved tolerance to both stresses. Collectively, our findings indicate that GmFIP37 acts as a key component of the soybean m6A methyltransferase complex and positively regulates soybean responses to salt and drought stresses by modulating m6A modification. This study provides novel insights into the epigenetic regulatory mechanisms underlying soybean abiotic stress tolerance and lays a foundation for the genetic improvement of stress-resistant soybean varieties.