RAP2.6 negatively regulates Arabidopsis submergence tolerance through GSNOR1-dependent redox and hormonal signaling
Group VII ETHYLENE RESPONSE FACTORs (ERFVIIs) are central regulators of plant responses to oxygen deprivation. However, the contributions of many other APETALA2 (AP2)/ERF transcription factors to hypoxia and flooding responses remain poorly understood. Here, we identify the group X ERF transcription factor RAP2.6 as a negative regulator of submergence tolerance in Arabidopsis thaliana. RAP2.6 expression declined under hypoxia, and plants overexpressing RAP2.6 exhibited reduced survival following dark submergence, whereas the rap2.6-1 loss-of-function mutant showed enhanced tolerance to submergence, hypoxia, and ethanol treatment. Enhanced tolerance of rap2.6-1 was associated with reduced membrane injury, maintenance of photosynthetic pigments and soluble sugars, and extensive metabolic remodeling. RAP2.6 overexpression altered nitric oxide (NO), S-nitrosothiol (SNO), and ethylene accumulation during submergence and was associated with greater oxidative damage and enhanced abscisic acid (ABA)-responsive gene expression. Genetic analyses using S-NITROSOGLUTATHIONE (GSNO) REDUCTASE 1 (GSNOR1) gain- and loss-of-function backgrounds demonstrated that GSNOR1-dependent GSNO homeostasis strongly modified RAP2.6-dependent submergence responses. Increased GSNOR1 activity suppressed the submergence-sensitive phenotype of RAP2.6-overexpressing plants, reduced nitro-oxidative stress, and restored carbohydrate reserves, whereas loss of GSNOR1 activity abolished the enhanced tolerance of rap2.6-1. GSNOR1 also modified RAP2.6-dependent expression of genes associated with oxygen sensing and ABA signaling, while its protective effect was not explained solely by changes in ethylene accumulation. Together, these findings identify RAP2.6 as a regulatory component of the low-oxygen response and reveal a functional interaction between RAP2.6 and GSNOR1-dependent redox signaling that coordinates plant hormonal, metabolic, and oxidative responses during submergence.