Hydrogen sulfide orchestrates compartmentalized carbon flux reprogramming to sustain NADPH-dependent redox homeostasis under salt stress in rice.

Hydrogen sulfide (H2S) is recognized as an important redox signaling molecule in plant stress responses, yet how it coordinates metabolic regulation across subcellular compartments remains poorly understood. Here, using rice as a model system, we investigated whether H2S functions as a spatial metabolic signal that integrates carbon flux reprogramming with NADPH-dependent redox homeostasis under salt stress. By combining subcellular H2S quantification, persulfidation profiling, enzyme activity assays, and targeted metabolite analyses, we identified fructose-1,6-bisphosphate aldolase (FBA) as a central regulatory node of compartment-specific H2S signaling. H2S preferentially accumulated in chloroplasts and directly modified both cytosolic and chloroplastic FBA isozymes via persulfidation, but with differential functional outcomes. In chloroplasts, persulfidation suppressed FBA activity, constrained Calvin-Benson cycle regeneration, and redirected NADPH from carbon assimilation toward glutathione-based antioxidant defense. In the cytosol, H2S modulated FBA activity and upstream metabolic enzymes, promoting glucose-6-phosphate flux into the oxidative pentose phosphate pathway and enhancing NADPH production to sustain redox buffering. Together, these findings reveal that H2S operates as a compartment-specific metabolic coordinator that integrates carbon metabolism with NADPH allocation, thereby enabling plants to prioritize redox stability over growth during salt stress.