Extensive mitochondrial specific transcription of the Brassica campestris mitochondrial genome

We constructed a complete transcriptional map of the 218 kb Brassica campestris (turnip) mitochondrial genome. Twenty-four abundant and positionally distinct transcripts larger than 500 nucleotides were identified by Northern analyses. Approximately 30% (61 kb) of the genome is highly transcribed. In addition, a number of less abundant transcripts, many of which overlap with each other and with the major transcripts, were also detected. If each abundant transcript represents a distinct rRNA or protein species, then plant mitochondria would appear to encode a significantly larger number of proteins than do animal mitochondria. Although B. campestris mitochondrial DNA contains a number of chloroplast DNA-derived sequences, none of these chloroplast sequences appear to be transcribed within the mitochondrion. We determined the positions of 12 genes in the B. campestris mitochondrial genome. The order of these genes in B. campestris is completely different than in maize (1) and spinach (2).