Previously, we found that flooding leads to an increase in APX enzymatic activity in the roots of eggplants. The objectives of this work were to clone the ascorbate peroxidase (APX) gene, and measure the regulation of APX gene expression in different tissues of eggplant under flooding stress conditions. Different tissues from eggplants displayed wide variations in their expression profiles using Real-Time PCR. The highest level of APX transcripts were detected in roots of EG117 at 72 h of flooding treatment. The differential expressions of each tissue and genotype were directly associated with flooding stress responses. After screening and comparing APX gene sequences at the NCBI database, the degenerate primer sets designed from tomato and potato were used to amplify the APX cDNA of eggplant with the reverse-transcription PCR method. The completion of a full-length of APX cDNA was performed using 5' and 3' rapid amplification of cDNA ends (PACE) technique. The open reading frame of cDNA clone was 753 base pair long encoding a cytosolic APX (cAPX). The sequence of eggplant APX gene had 96%, 95%, 93% and 91% homology to that from the potato, tomato, pepper and tobacco APX gene, respectively. A phylogenetic analysis of the deduced amino acid sequence of APX by Neighbor-Joining method indicated that the plant cAPXs diverge into two major clusters, and eggplant cDNA is more closely related to potato than to tomato. Southern blot analysis revealed that the eggplant gene encoding APX had two copies. These results indicate that the cAPX of eggplant may be involved in hydrogen peroxide-detoxification and thus helps overcome the stress induced by flooding.
