Abstract
Organelle genomes show remarkable variation in architecture and coding content, yet their nucleotide composition is relatively unvarying across the eukaryotic domain, with most having a high adenine and thymine (AT) content. Recent studies, however, have uncovered guanine and cytosine (GC)-rich mitochondrial and plastid genomes. These sequences come from a small but eclectic list of species, including certain green plants and animals. Here, I review GC-rich organelle DNAs and the insights they have provided into the evolution of nucleotide landscape. I emphasize that GC-biased mitochondrial and plastid DNAs are more widespread than once thought, sometimes occurring together in the same species, and suggest that the forces biasing their nucleotide content can differ both among and within lineages, and may be associated with specific genome architectural features and life history traits.
Highlights
Mitochondria and plastids are the products of ancient endosymbiotic events, involving a proteobacterium and a cyanobacterium, respectively (Lang et al, 1999; Palmer, 2003)
Unraveling the mechanism responsible for their guanine and cytosine (GC) enrichment may help explain the near-ubiquity of AT-rich mitochondrial and plastid genomes throughout the eukaryotic domain, and could give insights into other aspects organelle genome architecture, such as the origins of RNA editing
The polar trebouxiophyte Coccomyxa subellipsoidea C-169 has a GC-bias in both its mitochondrial and plastid compartments (53 and 51% GC, respectively), and organelle gene sequencing indicate that Coccomyxa chodatii and Coccomyxa rayssiae have GC-rich organelle DNAs as well (Smith et al, 2011)
Summary
Organelle genomes show remarkable variation in architecture and coding content, yet their nucleotide composition is relatively unvarying across the eukaryotic domain, with most having a high adenine and thymine (AT) content. Recent studies have uncovered guanine and cytosine (GC)-rich mitochondrial and plastid genomes.These sequences come from a small but eclectic list of species, including certain green plants and animals. I review GC-rich organelle DNAs and the insights they have provided into the evolution of nucleotide landscape. I emphasize that GC-biased mitochondrial and plastid DNAs are more widespread than once thought, sometimes occurring together in the same species, and suggest that the forces biasing their nucleotide content can differ both among and within lineages, and may be associated with specific genome architectural features and life history traits
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