Molecular cloning of the gene (SodCc1) that encodes a cytosolic copper/zinc-superoxide dismutase from rice (Oryza sativa L.).

SOD (superoxide:superoxide oxidoreductase; EC 1.15.1.1) is considered a crucial component in biological defense against oxidative stress (Bowler et al., 1992). In higher plants, there are three known forms of the enzyme: Cu/Zn-, Mn-, and Fe-SODs. These SOD activities are typically associated with specific subcellular locations such as mitochondria (Mn-SOD), plastids (Cu/Zn-SOD and/or FeSOD), and the cytosol (Cu/Zn-SOD) and display a differential expression pattern in response to environmental and chemical stresses (Perl-Treves and Galun, 1991; Tsang et al., 1991). We have isolated SOD cDNA clones for a mitochondrial Mn protein and two cytosolic Cu/Zn isozymes from a rice (Oryza sativa L. cv Nipponbare) cDNA library prepared from developing seeds (Sakamoto et al., 1992a, 1993). Two nuclear genes (SodCcl and SodCc2); which corresponded to the cytosolic Cu/Zn-SOD cDNAs, were also obtained and the exon/intron organization of the SodCc2 gene was characterized (Sakamoto et al., 1992b). To our knowledge, this is the only complete analysis of a plant Cu/Zn-SOD gene structure. W e present the identification of the gene, SodCcl, that codes for an another cytosolic Cu/Zn-SOD in rice (Table I). Isolation of the genomic A clone (gSOD27) containing the SodCcZ gene was described previously (Sakamoto et al., 1992b). Sequence analysis of the structural region revealed that the SodCcl transcribed region spans a chromosomal region over 3 kb long and is segmented by seven introns, the first of which appeared in the 5' transcribed but untranslated region. The borders between exons and introns were in full agreement with the GT-AG rule. The exon/ intron structure was identical between the SodCcl and the