Ammonium mitigates cadmium toxicity by activating the bZIP20-APX2/CATA transcriptional module in rice seedlings in an...

The amelioration of cadmium (Cd²⁺) toxicity in plants by ammonium (NH₄⁺) has been widely investigated. However, the molecular mechanisms underpinning this amelioration have remained ambiguous. Here, we found that NH₄⁺ significantly reduces Cd²⁺ accumulation and enhances antioxidant capacity by increasing ABA accumulation, which, in turn, improves Cd²⁺ tolerance in rice seedlings. A combination of qPCR, yeast-one-hybrid and dual-luciferase assays, and CUT&RUN-qPCR methods demonstrates that OsbZIP20 directly binds to the promoters of OsAPX2 and OsCATA, activating their transcription, and we show that the process requires phosphorylation modification of OsbZIP20 by OsSAPK9. Under Cd²⁺ stress, Osbzip20 and Ossapk9 mutants show reduced peroxidase and catalase activities, higher H₂O₂ accumulation, and reduced Cd²⁺ tolerance. In sum, our results elucidate a novel mechanism by which NH₄⁺ enhances Cd²⁺ resistance, through ABA-SAPK9-bZIP20-APX2/CATA, offering a new strategy for improving Cd²⁺ resistance in rice.