Evolution of a Pseudogene: Exclusive Survival of a Functional Mitochondrial nad7 Gene Supports Haplomitrium as the Earliest Liverwort Lineage and Proposes a Secondary Loss of RNA Editing in Marchantiidae
| Autor: | Ute Wahrmund, Monika Polsakiewicz, Milena Groth-Malonek, Volker Knoop |
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| Rok vydání: | 2007 |
| Předmět: |
Hepatophyta
Mitochondrial DNA food.ingredient DNA Plant Pseudogene Molecular Sequence Data Respiratory chain Biology DNA Mitochondrial Evolution Molecular Mitochondrial Proteins Marchantia polymorpha food Haplomitrium Genetics Amino Acid Sequence Molecular Biology Gene Phylogeny Ecology Evolution Behavior and Systematics Electron Transport Complex I Sequence Homology Amino Acid Exons Sequence Analysis DNA Group II intron biology.organism_classification Stop codon Codon Terminator RNA Editing Pseudogenes |
| Zdroj: | Molecular Biology and Evolution. 24:1068-1074 |
| ISSN: | 1537-1719 0737-4038 |
| DOI: | 10.1093/molbev/msm026 |
| Popis: | Gene transfer from the mitochondrion into the nucleus is a corollary of the endosymbiont hypothesis. The frequent and independent transfer of genes for mitochondrial ribosomal proteins is well documented with many examples in angiosperms, whereas transfer of genes for components of the respiratory chain is a rarity. A notable exception is the nad7 gene, encoding subunit 7 of complex I, in the liverwort Marchantia polymorpha, which resides as a full-length, intron-carrying and transcribed, but nonspliced pseudogene in the chondriome, whereas its functional counterpart is nuclear encoded. To elucidate the patterns of pseudogene degeneration, we have investigated the mitochondrial nad7 locus in 12 other liverworts of broad phylogenetic distribution. We find that the mitochondrial nad7 gene is nonfunctional in 11 of them. However, the modes of pseudogene degeneration vary: whereas point mutations, accompanied by single-nucleotide indels, predominantly introduce stop codons into the reading frame in marchantiid liverworts, larger indels introduce frameshifts in the simple thalloid and leafy jungermanniid taxa. Most notably, however, the mitochondrial nad7 reading frame appears to be intact in the isolated liverwort genus Haplomitrium. Its functional expression is shown by cDNA analysis identifying typical RNA-editing events to reconstitute conserved codon identities and also confirming functional splicing of the 2 liverwort-specific group II introns. We interpret our results 1) to indicate the presence of a functional mitochondrial nad7 gene in the earliest land plants and strongly supporting a basal placement of Haplomitrium among the liverworts, 2) to indicate different modes of pseudogene degeneration and chondriome evolution in the later branching liverwort clades, 3) to suggest a surprisingly long maintenance of a nonfunctional gene in the presumed oldest group of land plants, and 4) to support the model of a secondary loss of RNA-editing activity in marchantiid liverworts. |
| Databáze: | OpenAIRE |
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