CLONING OF CDNAS ENCODING 2 PEROXIDASES OF ARABIDOPSIS-THALIANA AND THEIR ORGAN-SPECIFIC EXPRESSION

Two cDNAs, prxCa and prxEa, encoding peroxidase isozymes of Arabidopsis thaliana, ARP Ca and ARP Ea, respectively, were isolated by polymerase chain reaction using total RNA from stem and primers designed from genomic DNAs. The coding regions of the prxCa and prxEa cDNAs were identical to the putative exon regions in the genomic DNAs (Intapruk, C. et al., Gene, 98, 237-241, 1991) and contained 1092 and 1078 bp, respectively. The deduced amino acid sequences of ARP Ca and ARP Ea suggested the presence of leader peptides of 31 and 29 amino acid residues at the N-termini, and 308 and 307 amino acid residues in mature proteins, respectively. The amino acid sequence of ARP was compared with those of other plant peroxidases: ARP showed highly conserved alignment with the horseradish peroxidase (HRP) family (group 1), with 64 to 91% homology except for HRP n; lower similarity to rice, tobacco, cucumber, turnip, wheat and peanut peroxidases (group II) with 40 to 51% homology; and a very low level of homology of about 37% for potato and tomato peroxidases. The prxCa and prxEa were close to HRP neutral and basic isozyme genes, respectively, but the estimated isoelectric points of ARP Ca and ARP Ea showed values of 8.05 and 6.34, respectively. By Northern blot hybridization, the prxCa gene was shown to be expressed non-specific expression in many organs of A. thaliana, while the level of transcripts of the prxEa gene was found to be abundant in root but very low in leaf and stem.