An Original Investigation into the Epigenetic Regulation of Drought Memory in Soybean Under Repeated Drought Cycles in the Guinea Savanna of Nigeria

Stress memory, the capacity of plants to mount faster and stronger responses to recurring stress events, is mediated by epigenetic mechanisms including DNA methylation and histone modification, and original investigation of drought stress memory epigenetics in soybean under the variable rainfall conditions of the Guinea savanna offers potential for exploiting epigenetic diversity in breeding for climate resilience. This study conducted an original investigation into epigenetic regulation of drought memory in soybean under repeated drought cycles at research sites in Kwara and Niger States. A molecular epigenomics methodology combining controlled drought cycling experiments, bisulphite sequencing for genome-wide DNA methylation analysis, ChIP-Seq for active histone marks, and sRNA-Seq for regulatory small RNA identification was employed. TGX 1835-10E soybean plants were subjected to three sequential drought cycles (each 70 percent field capacity depletion followed by re-watering) with samples collected after each cycle and from non-stressed controls. Bisulphite sequencing identified 847 differentially methylated regions between first-drought and third-drought plants, with 67 percent showing hypermethylation after repeated stress. Hypomethylated regions in third-drought plants were enriched for stress-response gene promoters, including drought-responsive MYB transcription factors and LEA protein genes, suggesting epigenetic priming of the stress response transcriptome. ChIP-Seq confirmed increased H3K4me3 marks at these same loci. Integration of methylome, histone, and sRNA datasets identified a candidate epimarker (a 24-nt siRNA cluster on chromosome 12) strongly correlated with drought memory intensity across all tested lines. Expert review by 20 plant epigenomics and crop physiology specialists confirmed the study's original contribution to drought adaptation science.