Functional Divergence of Two Glutathione Peroxidase Genes in Oryza sativa

Plant glutathione peroxidases (GPX) are a group of enzymes that regulate levels of reactive oxygen species in cells and tissues,and protect them against oxidative damage.In this study,two GPX genes (OsGPX3 and OsGPX4) were cloned from Oryza sativa.The OsGPX3 and OsGPX4 genes encoded two proteins of 238 and 234 amino acid residues,with calculated molecular masses of 25.84 kDa and 25.07 kDa,respectively.Genomic sequence analysis showed OsGPX3 and OsGPX4 contained five introns.Reverse transcription PCR revealed that OsGPX3 and OsGPX4 were constitutive expression genes in O.sativa.The OsGPX3 and OsGPX4 proteins were overexpressed in E.coli,and were purified by Ni-affinity chromatography.The OsGPX3 and OsGPX4 proteins showed enzymatic activities towards substrates H₂O₂,tBOOH and COOH.However,OsGPX3 showed higher enzymatic activities to the three substrates than did OsGPX4,suggesting functional divergence between the OsGPX3 and OsGPX4 genes.