Characterization of a new mitochondrial plasmid from Fusarium proliferatum

A 10.3kb linear mitochondrial DNA plasmid designated pFP1 was isolated from Fusarium proliferatum. The DNA sequence of the plasmid consists of 10,336bp with perfect terminal inverted repeats of 400bp. Two major, non-overlapping ORFs were identified on opposite strands, encoding a phage-type RNA polymerase and a family B type DNA polymerase, respectively. One additional minor ORF encoding a putative highly basic protein was also identified. The copy number of pFP1, as determined by RT-PCR, ranged between 1.8 and 3.1 per mtDNA copies depending on the host strain. Real-time PCR analysis of a total of 400 cultures surviving ethidium bromide curing indicated that no plasmid-free strains could be obtained by this treatment. Further single spore selections of the survivors with reduced plasmid content were needed to obtain plasmid-free clones. No phenotypic differences were found between the wild-type strains and their plasmid-free progenies.