Hydrogen Gas Enhances Salinity Tolerance in Tomato Seedlings by Regulating the <i>S</i> ‐Nitrosylation of MEK1

ABSTRACT Hydrogen gas (H 2 ) effectively alleviates abiotic stress in horticultural plants. Protein S ‐nitrosylation, a key post‐translational modification, serves as a critical mechanism for nitric oxide (NO) to exert its biological function under adverse conditions. However, the relationship among H 2 , NO and S ‐nitrosylation in response to salt stress remains poorly understood. In this study, we demonstrate that NO participated in H 2 ‐enhanced salt tolerance in tomato seedlings ( Solanum lycopersicum cv. Micro‐Tom). H 2 triggered an increase in NO levels and S ‐nitrosothiol (SNO) content under salt stress, enhancing the enrichment of S ‐nitrosylated proteins. S ‐nitrosoproteomic analysis revealed that MEK1, a conserved MAPK component, was notably induced and S ‐nitrosylated by NO and H 2 under salt stress. Furthermore, SlMEK1 ‐overexpressing tomato lines exhibited enhanced salt stress tolerance, while knockout lines showed reduced tolerance, indicating the positive regulatory role of SlMEK1 in salt tolerance. Additionally, SlMEK1 may contribute to H 2 ‐enhanced salt tolerance. Meanwhile, MEK1 was shown to undergo S ‐nitrosylation at Cys 172, and this modification was involved in H 2 ‐enhanced salinity tolerance. Moreover, site‐specific mutation analysis at Cys 172 confirmed that MEK1 S ‐nitrosylation positively contributed to both intrinsic and H 2 ‐facilitated salt tolerance. Finally, S ‐nitrosylation of MEK1 increased its interaction with GSNOR, and H 2 further promoted this interaction under salt stress. Collectively, our findings indicate that H 2 may enhance the salinity tolerance in tomato seedlings by orchestrating the interplay between S ‐nitrosylated MEK1 and GSNOR.