Epigenomics and Non-Coding RNAs in Soybean Adaptation to Abiotic Stresses

This review presents soybean responses to drought, heat, and salinity within a signal–transcript–chromatin framework. In this framework, calcium/reactive oxygen species and abscisic acid cues converge on abscisic acid-responsive element binding factor (ABF/AREB), dehydration-responsive element binding protein (DREB), NAC, and heat shock factor (HSF) families. These processes are modulated by locus-specific chromatin and non-coding RNA layers. Base-resolved methylomes reveal a high level of CG methylation in the gene body, strong CHG methylation in heterochromatin, and dynamic CHH ‘islands’ at the borders of transposable elements. CHH methylation increases over that of transposable elements during seed development, and GmDMEa editing is associated with seed size. Chromatin studies in soybean and model species implicate the reconfiguration of salt-responsive histone H3 lysine 27 trimethylation (H3K27me3) in G. max and heat-linked H2A.Z dynamics at thermoresponsive promoters characterized in Arabidopsis and other plants, suggesting that a conserved chromatin layer likely operates in soybean. miR169–NF-YA, miR398–Cu/Zn Superoxide Dismutases(CSD)/copper chaperone of CSD(CCS), miR393–transporter inhibitor response1/auxin signaling F-box (TIR1/AFB), and miR396–growth regulating factors (GRF) operate across leaves, roots, and nodules. Overexpression of lncRNA77580 enhances drought tolerance, but with context-dependent trade-offs under salinity. Single-nucleus and spatial atlases anchor these circuits in cell types and microenvironments relevant to stress and symbiosis. We present translational routes, sentinel epimarkers (bisulfite amplicons, CUT&Tag), haplotype-by-epigenotype prediction, and precise cis-regulatory editing to accelerate marker development, genomic prediction and the breeding of resilient soybean varieties with stable yields.