MOLECULAR-CLONING AND CHARACTERIZATION OF 2 COMPLEMENTARY DNAS ENCODING PUTATIVE PEROXIDASES FROM RICE (ORYZA-SATIVA L) SHOOTS

PCR with oligonucleotide primers that corresponded to two highly homol ogous regions, in terms of amino acid sequence, of plant peroxidases w as used to amplify a specific DNA fragment from a mixture of rice (Ory za sativa L.) cDNAs. We then screened a cDNA library prepared from mRN As of rice shoots utilizing the product of PCR as probe. Two cDNA clon es, 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 si gnal peptide. Comparison of the amino acid sequences of the two rice p eroxidases showed that they are about 70% similar to each other but ar e only 40% to 50% similar to other plant peroxidases. RNA blot hybridi zation revealed that mRNAs that corresponded to prxRPA and prxRPN cDNA s accumulate at high levels in roots but only at low levels in stems a nd leaves. In various tissues of rice plants, levels of both mRNAs wer e stimulated by wounding and by ethephon. These results indicate that at least two isozymes of peroxidase are expressed not only in shoots b ut also in roots of rice plants, and that the expression of these gene s is influenced by ethylene which is the simplest plant hormone.