Formyl Tetrahydrofolate Deformylase Affects Hydrogen Peroxide Accumulation and Leaf Senescence by Regulating the Folate Status and Redox Homeostasis in Rice

It is well established that an abnormal tetrahydrofolate (THF) cycle causes the accumulation of hydrogen peroxide (HO) and leaf senescence, however, the molecular mechanism underlying this relationship remains largely unknown. Here, we reported a novel rice tetrahydrofolate cycle mutant, which exhibited HO accumulation and early leaf senescence phenotypes. Map-based cloning revealed that HPA1 encodes a tetrahydrofolate deformylase, and its deficiency led to the accumulation of tetrahydrofolate, 5-formyl tetrahydrofolate and 10-formyl tetrahydrofolate, in contrast, a decrease in 5,10-methenyl-tetrahydrofolate. The expression of tetrahydrofolate cycle-associated genes encoding serine hydroxymethyl transferase, glycine decarboxylase and 5-formyl tetrahydrofolate cycloligase was significantly down-regulated. In addition, the accumulation of HO in hpa1 was not caused by elevated glycolate oxidation. Proteomics and enzyme activity analyses further revealed that mitochondria oxidative phosphorylation complex I and complex V were differentially expressed in hpa1, which was consistent with the HO accumulation in hpa1. In a further feeding assay with exogenous glutathione (GSH), a non-enzymatic antioxidant that consumes HO, the HO accumulation and leaf senescence phenotypes of hpa1 were obviously compensated. Taken together, our findings suggest that the accumulation of HO in hpa1 may be mediated by an altered folate status and redox homeostasis, subsequently triggering leaf senescence.