S-nitrosoglutathione enhances rice tolerance to salt-submergence by coordinating ethylene, GA, and ABA accumulation and improving ion transport.

With unprecedented climate change, coastal overtopping is projected to increase up to 50-fold by 2100. Unlike complete flooding, overtopping imposes a salt-submergence stress for plants by combining oxygen (O2) deficiency with elemental toxicity. To address this, we investigated whether S-nitrosoglutathione (GSNO), a stable nitric oxide (NO) donor, could mitigate these dual stresses-submergence (Sub) and salt-mixed Sub (Salt + Sub)-in two Korean japonica rice varieties, Ilmi and Samgwang. Under Sub stress, both varieties relied on internode elongation and aerenchyma formation as escape strategies; however, these responses were significantly impaired under Salt + Sub. GSNO pretreatment effectively counteracted this impairment, not only by restoring the growth defects, but also improving overall biomass under both stresses. This response was mediated by ethylene, gibberellic acid (GA), and abscisic acid (ABA). Specifically, GSNO pretreatment reduced the level of ABA but increased the intermediates of GA and the relative expression of ethylene-related genes, ACO5 and EIN3, under both stress conditions. These changes led to downstream expression of marker genes associated with cell wall expansion, energy conservation, and ethylene signaling, particularly in Samgwang under Salt + Sub conditions. GSNO-treated Samgwang plants consistently outperformed Ilmi in terms of survival, largely due to improved detoxification of reactive oxygen species (ROS). Additionally, GSNO upregulated expression of Na+ transporter genes (SOS1, SOS2, HKT1, and NHX1), indicating improved Na+ extrusion and sequestration, thereby maintaining ion homeostasis during combined stress. Overall, GSNO conferred multifaceted protection against Sub and Salt + Sub stresses by improving hormonal balance, ROS-detoxification, and ion transport. These findings highlight GSNO's potential in conferring rice resilience to climate change-driven coastal challenges.