Elimination of mitochondrial mutations by sexual reproduction: two Podospora anserina mitochondrial mutants yield only wild-type progeny when mated.

In order to understand the transmission of mitochondrial mutations in sexual crosses of Podospora, we attempted to create compatible strains with defined mitochondrial mutations. A previously characterized mutant, Mn19, with a bipartite mitochondrial genome, served as the fertilizing parent in a cross with a mitochondrial deletion mutant, alphadelta5. Characterization of the deletion mutant is reported here. All six of the monokaryotic progeny isolated had neither parental defect but instead appeared to have inherited wild-type mitochondrial DNA. One of the progeny had a mitochondrial plasmid derived from intramolecular recombination between an 11-bp repeated mitochondrial sequence. Subsequent analysis using the polymerase chain reaction (PCR) identified rare undeleted wild-type mtDNA sequences in the maternal parent. The uniform inheritance of wild-type mitochondrial DNA suggests either an aggressive repair mechanism or else selective amplification and transmission of rare wild-type mtDNA molecules.