Molecular cloning and characterization of two complementary DNAs encoding putative peroxidases from rice (Oryza sativa L.) shoots

PCR with oligonucleotide primers that corresponded to two highly homologous regions, in terms of amino acid sequence, of plant peroxidases was used to amplify a specific DNA fragment from a mixture of rice (Oryza sativa L.) cDNAs. We then screened a cDNA library prepared from mRNAs of rice shoots utilizing the product of PCR as probe. Two cDNA clones, prxRPA and prxRPN, were isolated. They encode distinct isozymes of peroxidase. Sequence analysis indicated that the clones encode mature proteins of approximately 32 kDa, both of which possess a putative signal peptide. Comparison of the amino acid sequences of the two rice peroxidases showed that they are about 70% similar to each other but are only 40% to 50% similar to other plant peroxidases. RNA blot hybridization revealed that mRNAs that corresponded to prxRPA and prxRPN cDNAs accumulate at high levels in roots but only at low levels in stems and leaves. In various tissues of rice plants, levels of both mRNAs were stimulated by wounding and by ethephon. These results indicate that at least two isozymes of peroxidase are expressed not only in shoots but also in roots of rice plants, and that the expression of these genes is influenced by ethylene which is the simplest plant hormone.