Unraveling the regulatory mechanisms of ZnO nanoparticles in mitigating salt stress toxicity in cotton

Soil salinization is an escalating environmental challenge that severely impairs cotton productivity. Although ZnO nanoparticles (ZNPs) have shown promise in enhancing plant stress tolerance, their regulatory mechanisms in mitigating salt stress toxicity in cotton remain poorly understood. This study revealed the regulatory mechanism by which ZNPs significantly mitigate salt stress toxicity in cotton by integrating physiological, metabolic, and transcriptional responses. The synthesized ZNPs (hydrodynamic diameter: 28.3 ± 5.3 nm; ζ-potential: −41.5 ± 7.8 mV) partially restored plant height, leaf area, and chlorophyll content, improving photosynthetic performance under salt stress. Furthermore, ZNPs treatment enhanced antioxidant enzyme activities (SOD, POD, CAT, APX) and rebalanced phytohormone homeostasis—ameliorating declines in GA₃ and IAA, and attenuating excessive ABA accumulation. Time-resolved metabolomics (3277 metabolites) and transcriptomics (72,127 genes) revealed that ZNPs mitigate salt-induced metabolic perturbation and reprogram early transcriptional dynamics (notably within 12–24 h), forming co-expression modules enriched in flavonoid biosynthesis, hormone signaling, fatty acid biosynthesis, and photosynthesis pathways. Integrative analysis identified GhFAB , a fatty acid biosynthesis gene induced by ZNPs. Phenotypic assessments revealed that GhFAB-OE lines exhibited significantly enhanced salt tolerance, with increased chlorophyll content, plant height, and fresh weight under NaCl treatment, whereas its suppression increased salt sensitivity, validating its functional role, demonstrate that GhFAB acts as a positive regulator in ZNPs-mediated salt tolerance in cotton. Our findings provide a multi-dimensional understanding of ZNPs-mediated salt tolerance and offer a strategic framework for developing nanoparticle-based agronomic practices to improve crop tolerance in saline environments. • ZNPs improve the salt tolerance of cotton by enhancing photosynthesis and antioxidant defenses. • ZNPs stabilize metabolism and transcription under early salt stress. • GhFAB , a ZNPs-induced fatty acid biosynthesis gene, positively regulates salt tolerance. • Build a strategic framework for nanoparticle-based practices to enhance crop salt tolerance.