Dephosphorylation of CatC at Ser-18 improves salt and oxidative tolerance via promoting its tetramerization in rice

Catalase (CAT) is a vital antioxidant enzyme, while phosphorylation pivotally regulates its function. Many phosphosites have been identified in CAT, but their functions remained largely elusive. We functionally studied five phosphoserines (Ser-9, -10, -11, -18, and -205) of CatC in rice (Oryza sativa L.). Phospho-Ser-9 and - 11 and dephospho-Ser-18 promoted the enzymatic activity of CatC and enhanced oxidative and salt tolerance in yeast. Phosphorylation status of Ser-18 did not affect CatC peroxisomal targeting and stability, but dephospho-Ser-18 promoted CatC tetramerization to enhance its activity. Moreover, overexpression of dephospho-mimic form CatC^S18A in rice significantly improved the tolerance to salt and oxidative stresses by inhibiting the H₂O₂ accumulation. Together, these results elucidate the mechanism underlying dephosphorylation at Ser-18 promotes CatC activity and salt tolerance in rice. Ser-18 is a promising candidate phosphosite of CatC for breeding highly salt-tolerant rice.