Molecular cloning, expression analysis and chromosomal mapping of salt-responsive cDNAs in rice (Oryza sativa L.)

By using differential display PCR (DD-PCR) technique, two salt-inducible and one salt-repressed cDNA fragments were isolated from rice. The three eDNA fragments were characterized respectively as partial sequence of rice S-adenosylmethionine deearboxylase (SAMDC) gene, a new member of translation elongation factor 1A gene (named REF1A ), and a novel gene whose function is unknown (named SRG1). The full-length cDNA of SAMDC gene (named SAMDC1) was further isolated by RT-PCR approach and the deduced polypeptide was found to be homologous to SAMDC proteins of other plants, yeast and human. Northern hybridization revealed that expression of SAMDC1 and REF1A was induced, while SRG1 was dramatically repressed, by salinity stress. Southern blot analysis demonstrated that SAMDC1 and SRG1 were present as a single copy gene in rice genome, whereas rice REF1A gene was organized as a gene family. The REF1A, SAMDC1, and SRG1 genes were located on chromosome 3, 4, and 6 respectively by RFLP mapping approach using ZYQ