Finally, angiosperm mtDNAs incorporate foreign sequences remarkably often, from chloroplast and nuclear genomes of the same plant via intracellular gene transfer (Stern & Lonsdale, 1982 Knoop et al., 1996), and from other plants via horizontal gene transfer (Sanchez-Puerta et al., 2008 Rice et al., 2013 Xi et al., 2013). Of great functional and economic importance are those rearrangements that create functionally novel, chimeric genes involved in cytoplasmic male sterility (Kubo et al., 2011). Low-frequency recombination between short repeats is linked to the phenomenon of substoichiometric shifting of alternative configurations of the genome (Mackenzie, 2005 Arrieta-Montiel et al., 2009). On an organismal timescale, this leads to genomes consisting of a plethora of subgenomic and multimeric structures (Palmer & Shields, 1984 Backert et al., 1997 Maréchal & Brisson, 2010), whereas on an evolutionary timescale, it results in a highly scrambled gene order between closely related species and sometimes even within a species (Palmer & Herbon, 1988 Darracq et al., 2010 Sloan et al., 2012). Most angiosperm mtDNAs exhibit extraordinarily high rates of reciprocal, intra- and intermolecular recombination between large direct and inverted repeats, along with less frequent recombination across smaller repeats. We discuss the relevance of these findings to the surprisingly frequent occurrence of horizontal gene – and genome – transfer in angiosperm mitochondrial DNAs.Ī hallmark of angiosperm mitochondrial DNAs (mtDNAs) is their high rate of recombination and rearrangement, which is reflected in a number of unusual properties. Retention of a single form of most genes could be advantageous to minimize intracellular incompatibilities and/or reflect neutral forces that preferentially eliminate duplicated regions. Recombination produced a remarkably chimeric cybrid mitochondrial genome and occurred entirely via homologous mechanisms involving the double-strand break repair and/or break-induced replication pathways.It is also surprisingly large (41% and 64% larger than the parental genomes), yet contains single alleles for 90% of mitochondrial genes. This cybrid mitochondrial genome is highly recombinant, reflecting at least 30 crossovers and five gene conversions between its parental genomes.We conducted the first study in which the organellar genomes of a cybrid – between Nicotiana tabacum and Hyoscyamus niger – were sequenced and compared to those of its parents.Little is known about the extent, nature and consequences of mitochondrial recombination in these plants. An excellent experimental system for studying these events is offered by cybrid plants, in which parental mitochondria usually fuse and their genomes recombine. The structure and evolution of angiosperm mitochondrial genomes are driven by extremely high rates of recombination and rearrangement.
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