The intriguing evolutionary dynamics of plant mitochondrial DNA

The mitochondrial genome of plants is-in every respect and for yet unclear reasons-very different from the well-studied one of animals. Thanks to next-generation sequencing technologies, Davila et al. precisely characterized the role played by recombination and DNA repair in controlling mitochondrial variations in Arabidopsis thaliana, thus opening new perspectives on the long-term evolution of this intriguing genome. See research article: http://www.biomedcentral.com/1741-7007/9/64 The mitochondrial genome of plants is a challenge to molecular evolutionary biologists. Its content is highly dynamic: plant mitochondrial DNA (mtDNA) is large and variable in size (200 to 2,500 kb), contains many introns and repeated elements (typically 90% of the total sequence), and experiences frequent gene gain/loss/transfer/duplication, and genome rearrangements [1]. Its nucleotide substitution rate, paradoxically, is remarkably low-even lower than for nuclear DNA. These features are in sharp contrast with the highly studied mtDNA of animals, which is small-sized, structurally conserved, devoid of selfish elements, and has a very fast nucleotide substitution rate [2]. Why these two genomes behave so differently is one of the most head-scratching questions of current comparative genomics. The study by Davila et al. [3] contributes a potentially decisive argument by connecting the plant mtDNA mutation rate to yet another intriguing feature of this organellar genome-recombination.