Plant Mitochondrial Mutations

The complex mitochondrial genomes of angiosperms tend to rearrange, leading to rapid structural evolution and to visible mutations. The observed mutations include those affecting growth and morphology, as well as male fertility. The abnormal growth mutations are usually associated with defects in essential mitochondrial genes. In contrast, cytoplasmic male sterility (CMS) usually results from the de novo expression of chimeric open reading frames (ORFs) in rearranged mitochondrial genomes. The expression of the CMS-chimeric ORFs can be modified by nuclear restorer-of-fertility (Rf) genes. Most of the Rf genes described to date are rapidly evolving members of a class of genes encoding pentatricopeptide repeat (PPR) proteins. Plants may also revert to fertility following mitochondrial DNA (mtDNA) rearrangements that disrupt the sterility-associated region. Alternatively, subgenomes containing a CMS-ORF may be lost or highly suppressed. In many cases, the mtDNA rearrangements that lead to phenotypic changes are mediated by events involving short or microhomologous repeats. In this chapter, we emphasize work on cytoplasmic male sterility, including cytoplasmic reversion to fertility and nuclear restoration of fertility.