Poly(acrylic Acid) Coated Mn3O4 Nanozymes Enhanced High Light Stress Tolerance in Cotton by Scavenging ROS and Down-Regulating the Expression Level of GhADF7

High light stress is common during plant production. However, we still lack of powerful tools to deal with high light stress. In this study, poly(acrylic acid) coated Mn3O4 nanoparticles (PMO) were used to increase high light tolerance of cotton. Our results showed that the fluorescence intensity of hydrogen peroxide (H2O2), hydroxyl radical, and superoxide anion (O2•-) was significantly lower in PMO treated cotton plants than control plants under high light, accompanied with increased activities of peroxidase and catalase in PMO treated cotton plants. Further, under high-light stress, PMO treatment significantly downregulated actin depolymerization factor GhADF7 expression by 64.0% (first true leaf) and 41.0% (second true leaf) compared with the control, accompanied by a marked increase in actin filament (AF) fluorescence intensity and integrated density. Under normal growth conditions, foliar application of actin polymerization inhibitor and excessive H2O2 demonstrated that AF depolymerization led to increased ROS accumulation, whereas PMO effectively alleviated high-light-induced ROS accumulation. This result indicated that the ROS content and the stability of AF skeleton were mutually affected. Moreover, cotton plants with silencing of GhADF7 showed increased actin filament fluorescence intensity and integrated density while reducing H2O2 and O2•- levels in seedlings under high-light stress. Collectively, these results demonstrate that PMO enhances high-light tolerance in cotton by suppressing AF depolymerization through downregulation of GhADF7 expression and modulation of ROS homeostasis, thereby maintaining cytoskeletal stability. It highlights the potential of nanotechnology approach as a powerful tool to resist plant high light stress.