Expressed sequence tags from cultured cells of rice (Oryza sativa L.) under stressed conditions: analysis of transcripts of genes engaged in ATP-generating pathways.

Large-scale sequencing of randomly selected cDNA clones was used to isolate numerous genes in rice (Oryza sativa L.). Total RNA used for cDNA synthesis was prepared from suspension-cultured cells of rice grown under stressed conditions, such as in saline or nitrogen-starvation conditions. A total of 780 cDNA clones were partially sequenced and about 15% could be identified as putative genes. In the library constructed under saline conditions, we identified several genes associated with signal transduction, such as protein kinase and small GTP-binding protein genes. Many stress-related genes were isolated from both the saline and nitrogen-starvation libraries. These results indicate that stress treatment of suspension-cultured cells makes it possible to efficiently isolate various types of plant genes. To examine the usefulness of such tagged cDNAs for the study of gene expression in a specific metabolic pathway, we analyzed mRNA levels of genes engaged in the ATP-generating pathways in cultured cells of rice under different stresses, such as 20% sucrose, salt stress, cold stress and nitrogen-starvation stress. The results suggest that the coordinated induction of several genes in key steps under stressed conditions may be essential for activation of the entire energy-producing pathway to maintain homeostasis in rice cells. Expressed sequence tags identified by random cDNA sequencing provide the opportunity to generate a transcript map of rice genes.