Cloning and molecular characterization of hrpX from Xanthomonas axonopodis pv. citri

The hrpX gene of plant pathogenic Xanthomonas species is essential for pathogenicity on host plants and to cause hypersensitive reaction on non-host plants. We cloned and analyzed a hrpX homologue, designated hrpXct, of X. axonopodis pv. citri, a pathogen of citrus canker. The open reading frame of hrpXct has 1431 bp in nucleotides which has a coding capacity of 476 amino acid residues with a molecular mass of 52.4 kDa. The predicted amino acid sequence of HrpXct has 90% identity to the AraC family type transcriptional activator protein HrpXc of X. campestris pv. campestris, 95% to HrpXo of X. oryzae pv. oryzae and 97% to X. vesicatoria. These findings clearly indicate and confirm that the structure of the hrpX genes in plant pathogenic Xanthomonas species is highly conserved.