Isolation and Molecular Characterization of a Putative Ascorbate Peroxidase Gene from Citrus

Ascorbate peroxidase is the key enzyme in detoxifying hydrogen peroxide (H2O2) and other reactive oxygen species from chloroplast and cytosol. A cDNA encoding a putative citrus ascorbate peroxidase, APXcit was isolated from mature ‘Dancy’ tangerine (Citrus reticulata Blanco) juice vesicles using differential display reverse transcription-polymerase chain reaction. The full-length APXcit sequence was composed of 1,082 bp nucleotides, including an open reading frame of 753 bp, putatively encoding a protein of 250 amino acids with a predicted molecular mass of 27 kDa. The 5′ untranslated region consisted of 90 nucleotides and the 3′ untranslated region of 239. The genomic clone of 2,457 bp was composed of 8 introns and 9 exons. A homology search for APXcit at the GenBank database showed high similarity to ascorbate peroxidase from several plant species. Southern analysis revealed that there may be 2–4 APXcit gene copies in citrus.