The construction of plasmids suitable for searching important rice genes.

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In order to clone unknown but agriculturally useful genes, we have constructed a plasmid suitable for transferred-DNA-mediated insertional mutagenesis. It has a 35S promoter and a chloramphenicol acetyl transferase gene which are active in plant cells, and a replication origin and a ampicillin resistant gene which are active in bacterial cells. We tried to transform this 7.6 kb long plasmid into rice culture cells by a particle gun, but we could not obtain transformants. The mitochondrial genomes of higher plants are much larger and more complex than those of other eukaryotic organisms. However, number of identified genes are limited. We speculated that mitochondrial DNA codes more active genes and searched unidentified important genes in rice mitochondrial DNA.First, we constructed a transcription map of the mitochondrial genome from rice. Then we determined nucleotide sequence the area in where the RNA is transcribed but genes are not identified. We found nad9, the gene for NADH dehydrogenase subunit 9, by this method.