Molecular cloning and characterization of rice 6-phosphogluconate dehydrogenase gene that is up-regulated by salt stress.

The pentose phosphate pathway (PPP) is the important metabolism pathway in plant. In the present study, a cDNA encoding one of the key enzymes of PPP, 6-phosphogluconate dehydrogenase(6PGDH), was isolated from rice and designated as Os6PGDH. The Os6PGDH encoding protein is a cytosolic isoenzyme according to the absence of plastid transit peptide at the N-terminus. The full-length cDNA of 1751 bp encodes 480 amino acids and its putative protein sequence is 94%, 84% and 83% identical to maize, spinach and alfalfa 6PGDHs respectively. Comparison of the cloned mRNA sequence with that of the genomic sequence from the Rice Genome Project showed a simple genomic organization devoid of introns in the translated region of the gene. RT-PCR experiments revealed that Os6PGDH expression was high in inflorescence, low in root and embryos but almost absent in leaves. Furthermore, Os6PGDH was up-regulated in the shoots under salt stress. It is suggested that 6PGDH in plant may play an important role in cell division and salt response.