A mitochondrial plasmid and plasmid-like RNA and DNA polymerases encoded within the mitochondrial genome of carrot (Daucus carota L.)

The mitochondrial genome of mitochondrial type (mitotype) SW3 of carrot (Daucus carota L.) encodes intact reading frames for a RNA polymerase (Rpo) and a DNA polymerase (Dpo) similar to those encoded by linear mitochondrial plasmids from plants. A BLAST search of translated nucleotide sequences in GenBank revealed previously unreported plasmid-like Rpo or Dpo sequence fragments in many plant mitochondrial DNAs. Phylogenetic analyses of the relationships between mitochondrial (mt)DNA-encoded and plasmid-encoded Rpos and Dpos from plants suggest that the mitochondrial sequences were derived from integrated plant plasmid sequences. A linear mitochondrial plasmid was detected in a different mitotype (FG21) of carrot by Southern hybridization of the Rpo and Dpo to undigested mtDNAs. Transcripts of the mtDNA-encoded Rpo and Dpo in mitotype SW3 were detected by RT-PCR.