Rapeseed mitochondrial ccb206, a gene involved in cytochrome c biogenesis, is co-transcribed with the nad3 and rps12 genes: organization, transcription, and RNA editing of the nad3/rps12/ccb206 locus.

We describe here the structure and expression of the nad3/rps12/ccb206 locus in the mitochondrial genomes of rapeseed (Brassica napus L.) and related species. In the rapeseed mitochondrial genome there are three tandemly located open reading frames for subunit 3 of NADH dehydrogenase (nad3), the S12 subunit protein of the mitochondrial ribosome (rps12), and a homologue of one subunit of the ABC-heme transporter (ccb206). The gene organization of the nad3/rps12/ccb206 locus found in rapeseed mitochondria is not conserved in Arabidopsis thaliana mitochondria, where the ccb206 and nad3/rps12 loci are separated from each other. We show here that the rapeseed gene-organization pattern is also present in other Brassica species, but not in radish, a species very closely related to Brassica. Northern hybridization and RT-PCR analyses indicate that these three mitochondrial genes are possibly co-transcribed. Ten, seven, and 39 C-to-U RNA editing events occur in the rapeseed nad3, rps12, and ccb206 transcripts, respectively. Finally we show that codon position 21 of nad3 is edited in a highly species-specific manner among related Brassica species, including rapeseed and radish.