The mystery of the rings: structure and replication of mitochondrial genomes from higher plants

Higher plant mitochondrial genomes are unique in their size, complexity and evolutionary dynamics. However, in spite of the existence of physical maps, the structural organization of the mitochondrial genome in vivo is not fully understood. The molecules observed are mainly linear or complex, and some of them are much larger than predicted from the genome size. In addition, circular DNA species are found in a continuous size distribution up to >100 kb — although this is heavily skewed towards small molecules. There is a high single-stranded DNA content, and both theta- and sigma-modes of replication have been reported. Recombination between large and small repeats as well as amplification by replication appear to contribute considerably to mitochondrial genome diversity.