The higher plant mitochondrial genome contains in the order of 50 proteins coding genes scattered throughout the genome and while much of the genome is transcribed, regulatory control is primarily exercised posttranscriptionally at the level of the ribonucleic acid (RNA) or protein turnover. In some plant species aberrant recombination events in the mitochondrial genome generate novel open reading frames, expressed as variant polypeptides, which in some cases lead to failure to produce functional pollen, a trait that has been exploited in plant breeding to produce F1 hybrid crops.