Histone H3K27 trimethylation modulates the cotton response to KCl-induced ionic stress

Potassium (K+), an essential macronutrient for plant growth and stress adaptation, becomes physiologically stressful when overaccumulated in soil. While K fertilization enhances cotton (Gossypium hirsutum) fiber quality and yield, the consequential KCl-induced ionic stress has emerged as a critical agricultural challenge demanding molecular-level resolution. This study unveils the previously unexplored epigenetic mechanisms mediated by histone H3 lysine 27 trimethylation (H3K27me3) in cotton's adaptation to KCl stress. Through integrated cleavage under targets and tagmentation (CUT&Tag) chromatin profiling and transcriptome sequencing, we demonstrate that KCl stress triggers genome-wide attenuation of H3K27me3 deposition, concomitant with characteristic stress phenotypes in cotton seedlings. Suppression of H3K27me3 using RDS 3434 significantly ameliorated KCl-induced physiological damage, thereby supporting a functional correlation between this epigenetic mark and stress tolerance. Mechanistic analyses revealed 48 genes exhibiting inverse correlation between H3K27me3 enrichment and transcriptional activation, including 2 that encode pivotal salt-tolerance regulators: Glutathione Synthase1 (GhGSH1) and Salt-Related MYB1 (GhSRM1). Virus-induced gene silencing validation confirmed these H3K27me3-associated genes as essential components of cotton's ionic stress response network. Our findings delineate the epigenetic landscape associated with KCl stress adaptation and highlight H3K27me3-mediated chromatin remodeling as a critical regulatory layer in plant abiotic stress responses. This work provides insights into epigenetic engineering strategies for developing stress-resilient cotton cultivars.