A cDNA clone encoding a rice catalase isozyme.

Catalase (H202: H202 oxidoreductase, EC 1.11.1.6) is a heme-containing enzyme that converts H202 into oxygen and water. In plants, catalase is involved in scavenging H202, which is generated during the course of photorespiration and P-oxidation of fatty acids. It also plays an important role in detoxification of active oxygen species that are generated by various environmental stresses (Scandalios, 1990). Many higher plants have multiple isoforms of catalase. Maize catalase is encoded by three distinct genes whose expression is regulated differentially in response to changes in either developmental phase or environmental conditions (Redinbaugh et al., 1988; Scandalios, 1990). Two isozymes of cotton catalase also exhibit different pattems of expression (Ni and Trelease, 1991a). A rice catalase cDNA (CatA) has been isolated from immature seeds (Mori et al., 1992). Here we report the sequence of another rice catalase cDNA, which covers nearly the full length of its corresponding mRNA, 282 nucleotides of which are identical with those found in a partial cDNA sequence from suspension-cultured rice cells reported as accession number D10425 (Uchimiya et al., 1992). A cDNA library in XZapII vector was constructed from poly(A)+ RNA prepared from rice seedlings grown in the dark for 4 d. PCR was performed on cDNAs prepared as described above using oligonucleotide primers synthesized on the basis of the conserved sequences of catalases from maize (Redinbaugh et al., 1988), cotton (Ni and Trelease, 1991b), pea (Isin and Allen, 1991), and sweet potato (Sakajo et al., 1987). A PCR product with an expected size of 550 bp was obtained. Partia1 sequencing of this product revealed that it was highly homologous but not identical with rice CatA. Using this fragment, the cDNA library was screened. Three positive clones were isolated, one of which (named CatB) was sequenced (Table I). It is 1854 bp long and contains an open reading frame encoding a protein of 492 amino acids. The nucleotide sequence is 63.6% identical with rice CatA and 80.7% with maize Cat l . It contains a segment completely identical, except for one base, with that in a partial sequence (accession No. D10425) of a rice catalase gene. The deduced amino acid sequence shows high homologies of 71.1, 93.3, 63.3, and 67.4% to rice CATA, maize CATI, CAT2, and CAT3, respectively. A11 of the amino acid residues involved in catalytic activity ( H ~ s ~ ~ , Ser113, AS^'^^) and heme binding (Va173, Arg"', Tyr1I4, PheI5', Pr0335, Arg353, Tyr357) (Fita and Rossman, 1985) are conserved in rice CATB as well as the published sequences