Abstract

Catalase (CAT) plays a central role in maintaining H 2 O 2 homeostasis during stress response, yet how phosphatase-mediated dephosphorylation modulates CAT activity and stability remains unclear. Here, we identified a protein phosphatase OsPP1a as a positive regulator of salt tolerance in rice ( Oryza sativa L.). OsPP1a directly dephosphorylates CatC at Thr-292 in the peroxisome, thereby enhancing its stability and enzymatic activity by inhibiting E3 ubiquitin ligase APIP6-mediated ubiquitination and degradation. Consistently, OsPP1a -overexpressing lines exhibit enhanced salt and oxidative tolerance with a lower phospho-threonine level of CATs. Phosphatase activity and seminal root growth assays further indicate that OsPP1a acts as a critical regulator balancing salt tolerance and growth in rice. Importantly, OsPP1a overexpression markedly mitigates salt-induced grain yield loss. Together, these results shed light on the mechanisms of CAT switch-on and stabilization by phosphatases and provide a strategy for breeding highly salt-tolerant rice.