ISOLATION, MOLECULAR CHARACTERIZATION AND CHROMOSOMAL MAPPING OF COLD-INDUCIBLE cDNA CLONES IN RICE

Cytogenetics Division,National Institute of Agricultural Science and Technology,Suwon 441-707, Korea

To identify low-temperature-regulated genes presumed to be important for the increased tolerance to low temperature, differentially expressed mRNAs were isolated and analyzed. cDNA clones from cold-treated cDNA library were randomly selected and differentially screened using radiolabeled first-strand cDNA probes constructed from mRNA isolated from ABA-, cold-, and salt-treated rice seedlings. Of approximately 50 differentially expressed clones were identified, and the responses for each stress appeared a lot different patterns. Although ABA hormone has been known as common mediator of water-deficit, cold stress seems somewhat different to other dehydration stresses. All of these cDNAs were partially sequenced and grouped into families according to their expression patterns. They have been categorized into not only ABA-dependent cold inducible expression but also ABA-independent stress inducible expression. ABA-synergistic induction appeared in cold inducible clones even though they were not induced by ABA treatment alone. Sequence alignment and homology searches indicated that some of them involved in signal transduction pathways responding to dehydration signaling, including protein kinase, protein phosphatase, and DNA binding transcription factors. Chitinase, ferritin, germin, catalase and peroxidase, etc were reported to be associated with stress responses in plants. Metabolism related proteins such as choline kinase, sedoheptulose- 1,7-bisphosphatase, isoflavon reductase homologue protein, sucrose phosphate synthase and GAPD were also identified as inducible genes. It has been reported that some hydrolytic enzymes were induced in environmental stress because of protein turnover. Our results also showed that they were up-regulated by those diverse stresses. In the chromosomal mapping with 'MG RI population', the cDNA clones were evenly positioned in rice chromosomes. The analysis of these cold- stress inducible genes as well as ABA and salt stress inducible genes from rice and the expression level of each treatment will be discussed.