Molecular cloning of a cytosolic ascorbate peroxidase cDNA from cell cultures of sweetpotato and its expression in response to stress

A cDNA encoding a cytosolic ascorbate peroxidase (APX), swAPX1 , was isolated from cell cultures of sweetpotato (Ipomoea batatas) by cDNA library screening, and its expression in the context of various environmental stresses was investigated. swAPX1 contains an ORF of 250 amino acids (27.5 kDa) encoding a protein with a pI value of 5.32. The swAPX1 ORF does not code for a transit peptide, suggesting that the product is a cytosolic isoform. RNA blot analysis showed that swAPX1 gene is expressed in cultured cells and mature leaves, but not in stems, non-storage or storage roots of sweetpotato. The level of swAPX1 RNA progressively increased during cell growth in suspension cultures. In leaf tissues, the gene responded differentially to various abiotic stresses, as revealed by RT-PCR analysis. swAPX1 was highly induced in leaves by wounding, and treatment with methyl viologen (50 muM), hydrogen peroxide (440 mM), abscisic acid (ABA; 100 muM) or exposure to high temperature (37degreesC). In addition, the gene was strongly induced in the leaves following inoculation with a bacterial pathogen (Pectobacterium chrysanthemi). These results indicate that swAPX1 may be involved in hydrogen peroxide-detoxification and thus help to overcome the oxidative stress induced by abiotic and biotic stresses.