Nucleotide sequence of a rice genomic pyruvate decarboxylase gene that lacks introns: a pseudo-gene?

PDC (EC 4.1.1.1) is one of the anaerobic polypeptides that are induced under anaerobic stress (Rivoal et al., 1989; Peschke and Sachs, 1993). In plants these anaerobic inductions are believed to be associated with the plant’s need for increasing sugar carbon flow through the glycolytic pathway to generate energy in the absence of oxygen (Good and Muench, 1993). During anaerobiosis, the glycolytic intermediate pyruvate is first converted into lactate (Davies et al., 1974). This results in the lowering of the cytoplasmic pH, which in tum activates PDC and inhibits lactate dehydrogenase (Roberts et al., 1984). As a result, pyruvate is nonoxidatively decarboxylated to acetaldehyde and carbon dioxide by PDC. Acetaldehyde, which is toxic, is further reduced to ethanol by alcohol dehydrogenase (EC 1.1.1.1). This step regenerates NAD+, which is essential for sustained operation of anaerobic glycolysis to produce ATP by substrate-leve1 phosphorylation. The role of PDC and alcohol dehydrogenase may be important in providing plants with tolerance to anoxic conditions that occur during submergence by flooding (Good and Muench, 1993). PDC genes ( p d c ) have been isolated from maize (Kelly, 1989; Peschke and Sachs, 1993), yeast (Kellerman et al., 1986), and bacteria (Conway et al., 1987). We have isolated three pdc genes from a rice genomic library. In this communication we report the cloning and sequencing of the pdc gene pdc3, which lacks any introns (Table I). This intron-less genomic p d c is not expressed and appears to be a pseudo-gene. Comparison of the amino acid sequence of this gene with that of rice p d c cDNAl (Hossain and Hodges,