Article

The complete mitochondrial genome sequence of the hornwort Megaceros aenigmaticus shows a mixed mode of conservative yet dynamic evolution in early land plant mitochondrial genomes.

Department of Ecology and Evolutionary Biology, The University Herbarium, University of Michigan, Ann Arbor, MI 48109-1048, USA.
Journal of Molecular Evolution (impact factor: 2.27). 07/2009; 68(6):665-78. DOI:10.1007/s00239-009-9240-7 pp.665-78
Source: PubMed

ABSTRACT Land plants possess some of the most unusual mitochondrial genomes among eukaryotes. However, in early land plants these genomes resemble those of green and red algae or early eukaryotes. The question of when during land plant evolution the dramatic change in mtDNAs occurred remains unanswered. Here we report the first completely sequenced mitochondrial genome of the hornwort, Megaceros aenigmaticus, a member of the sister group of vascular plants. It is a circular molecule of 184,908 base pairs, with 32 protein genes, 3 rRNA genes, 17 tRNA genes, and 30 group II introns. The genome contains many genes arranged in the same order as in those of a liverwort, a moss, several green and red algae, and Reclinomonas americana, an early-branching eukaryote with the most ancestral form of mtDNA. In particular, the gene order between mtDNAs of the hornwort and Physcomitrella patens (moss) differs by only 8 inversions and translocations. However, the hornwort mtDNA possesses 4 derived features relative to green alga mtDNAs--increased genome size, RNA editing, intron gains, and gene losses--which were all likely acquired during the origin and early evolution of land plants. Overall, this genome and those of other 2 bryophytes show that mitochondrial genomes in early land plants, unlike their seed plant counterparts, exhibit a mixed mode of conservative yet dynamic evolution.

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Keywords

17 tRNA genes
 
2 bryophytes
 
3 rRNA genes
 
30 group II introns
 
32 protein genes
 
8 inversions
 
ancestral form
 
circular molecule
 
hornwort mtDNA possesses 4
 
Land plants
 
Megaceros aenigmaticus
 
Physcomitrella patens
 
Reclinomonas americana
 
red algae
 
RNA editing
 
seed plant counterparts
 
sister group
 
unanswered
 
unusual mitochondrial genomes
 
vascular plants