The rice auxin response factor OsARF12 coordinates ROS scavenging, photosynthetic protection, and Na⁺/K⁺ homeostasis under salt stress

Salt stress severely limits rice growth and productivity. Auxin signaling has a well-documented role in development, but its role in rice salt stress responses is far from clear. In this study, we identified OsARF12, an auxin response factor, as a critical positive regulator of salt tolerance in rice. Transcript analysis revealed salt-induced upregulation of OsARF12. More importantly, OsARF12 overexpression (OsARF12-OX) induced significantly increased survival rates and reduced biomass loss under 200 mmol L⁻¹ NaCl treatment compared with wild-type (WT) plants, and OsARF12 knockout (OsARF12-KO) using CRISPR-Cas9 showed the opposite tendency. Physiological analyses revealed that OsARF12-OX plants mitigated salt-induced oxidative damage by enhancing ROS scavenging capacity and promoting Na⁺/K⁺ homeostasis as well as through their superior photosynthetic efficiency under 200 mmol L⁻¹ NaCl treatment, which was consistent with the upregulation of differentially expressed genes involved in ROS scavenging, photosynthesis and ion transport pathways. Furthermore, auxin receptor genes or transcription inhibitor genes were upregulated or downregulated in OsARF12-OX lines compared with WT plants under salt stress, respectively. Biochemical assays indicated that OsARF12 acts as a transcriptional activator, directly binding to TGTC-box motifs in the promoters of the key ion transporters OsSOS1 and OsHKT1;5 to reduce shoot Na⁺ content and the Na⁺/K⁺ ratio, thereby increasing salt tolerance. These findings revealed the potential role of OsARF12 in increasing salt tolerance by integrating auxin signaling with ROS scavenging, ionic homeostasis and photosynthetic networks, offering valuable targets for breeding resilient rice varieties.