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Group II introns break new boundaries: presence in a bilaterian's genome.

Vallès Y, Halanych KM, Boore JL - PLoS ONE (2008)

Bottom Line: Here we report the first group II intron found in the mitochondrial genome of a bilaterian worm.This intron is found in the mtDNA of an annelid worm, (an undescribed species of Nephtys), where the complete sequence revealed a 1819 bp group II intron inside the cox1 gene.We infer that this intron is the result of a recent horizontal gene transfer event from a viral or bacterial vector into the mitochondrial genome of Nephtys sp.

View Article: PubMed Central - PubMed

Affiliation: Department of Energy (DOE), Joint Genome Institute, Lawrence Berkeley National Laboratory, Walnut Creek, California, USA.

ABSTRACT
Group II introns are ribozymes, removing themselves from their primary transcripts, as well as mobile genetic elements, transposing via an RNA intermediate, and are thought to be the ancestors of spliceosomal introns. Although common in bacteria and most eukaryotic organelles, they have never been reported in any bilaterian animal genome, organellar or nuclear. Here we report the first group II intron found in the mitochondrial genome of a bilaterian worm. This location is especially surprising, since animal mitochondrial genomes are generally distinct from those of plants, fungi, and protists by being small and compact, and so are viewed as being highly streamlined, perhaps as a result of strong selective pressures for fast replication while establishing germ plasm during early development. This intron is found in the mtDNA of an annelid worm, (an undescribed species of Nephtys), where the complete sequence revealed a 1819 bp group II intron inside the cox1 gene. We infer that this intron is the result of a recent horizontal gene transfer event from a viral or bacterial vector into the mitochondrial genome of Nephtys sp. Our findings hold implications for understanding mechanisms, constraints, and selective pressures that account for patterns of animal mitochondrial genome evolution.

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Phylogenetic analysis of 71 group II intron ORFs. A maximum likelihood analysis of the amino acid sequence for 71 ORFs suggests the cox1 ORF718 of the marine centric diatom Thalassiosira pseudonana as sister to the Nephtys's ORF.Red stars indicate a bootstrap support ≥90. Names of taxa are indicated by the capital letter of the genus name, followed by species name and when applicable the intron location (specified in table 3).
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pone-0001488-g002: Phylogenetic analysis of 71 group II intron ORFs. A maximum likelihood analysis of the amino acid sequence for 71 ORFs suggests the cox1 ORF718 of the marine centric diatom Thalassiosira pseudonana as sister to the Nephtys's ORF.Red stars indicate a bootstrap support ≥90. Names of taxa are indicated by the capital letter of the genus name, followed by species name and when applicable the intron location (specified in table 3).

Mentions: Attempting to identify the evolutionary origin of the intron, we incorporated the inferred amino acid sequence of the intron's ORF (RT and partial maturase) into the alignment of Zimmerly et al. [19], which contains ORFs from other group II introns from bacterial and organellar genomes (both mitochondrial and chloroplast) from plants, fungi and protists (Table 3). In addition we have included the three most similar sequences in a search (using BLAST) of GenBank to the intron's ORF of Nephtys and of Trichoplax adhaerens in the alignment. A maximum likelihood phylogenetic analysis suggests that Nephtys's ORF is sister to the cox1 ORF718 of the marine centric diatom Thalassiosira pseudonana among those RT sequences available for comparison (Fig. 2). However, broader taxon sampling of group II introns is needed to reliably infer their evolutionary history.


Group II introns break new boundaries: presence in a bilaterian's genome.

Vallès Y, Halanych KM, Boore JL - PLoS ONE (2008)

Phylogenetic analysis of 71 group II intron ORFs. A maximum likelihood analysis of the amino acid sequence for 71 ORFs suggests the cox1 ORF718 of the marine centric diatom Thalassiosira pseudonana as sister to the Nephtys's ORF.Red stars indicate a bootstrap support ≥90. Names of taxa are indicated by the capital letter of the genus name, followed by species name and when applicable the intron location (specified in table 3).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2198948&req=5

pone-0001488-g002: Phylogenetic analysis of 71 group II intron ORFs. A maximum likelihood analysis of the amino acid sequence for 71 ORFs suggests the cox1 ORF718 of the marine centric diatom Thalassiosira pseudonana as sister to the Nephtys's ORF.Red stars indicate a bootstrap support ≥90. Names of taxa are indicated by the capital letter of the genus name, followed by species name and when applicable the intron location (specified in table 3).
Mentions: Attempting to identify the evolutionary origin of the intron, we incorporated the inferred amino acid sequence of the intron's ORF (RT and partial maturase) into the alignment of Zimmerly et al. [19], which contains ORFs from other group II introns from bacterial and organellar genomes (both mitochondrial and chloroplast) from plants, fungi and protists (Table 3). In addition we have included the three most similar sequences in a search (using BLAST) of GenBank to the intron's ORF of Nephtys and of Trichoplax adhaerens in the alignment. A maximum likelihood phylogenetic analysis suggests that Nephtys's ORF is sister to the cox1 ORF718 of the marine centric diatom Thalassiosira pseudonana among those RT sequences available for comparison (Fig. 2). However, broader taxon sampling of group II introns is needed to reliably infer their evolutionary history.

Bottom Line: Here we report the first group II intron found in the mitochondrial genome of a bilaterian worm.This intron is found in the mtDNA of an annelid worm, (an undescribed species of Nephtys), where the complete sequence revealed a 1819 bp group II intron inside the cox1 gene.We infer that this intron is the result of a recent horizontal gene transfer event from a viral or bacterial vector into the mitochondrial genome of Nephtys sp.

View Article: PubMed Central - PubMed

Affiliation: Department of Energy (DOE), Joint Genome Institute, Lawrence Berkeley National Laboratory, Walnut Creek, California, USA.

ABSTRACT
Group II introns are ribozymes, removing themselves from their primary transcripts, as well as mobile genetic elements, transposing via an RNA intermediate, and are thought to be the ancestors of spliceosomal introns. Although common in bacteria and most eukaryotic organelles, they have never been reported in any bilaterian animal genome, organellar or nuclear. Here we report the first group II intron found in the mitochondrial genome of a bilaterian worm. This location is especially surprising, since animal mitochondrial genomes are generally distinct from those of plants, fungi, and protists by being small and compact, and so are viewed as being highly streamlined, perhaps as a result of strong selective pressures for fast replication while establishing germ plasm during early development. This intron is found in the mtDNA of an annelid worm, (an undescribed species of Nephtys), where the complete sequence revealed a 1819 bp group II intron inside the cox1 gene. We infer that this intron is the result of a recent horizontal gene transfer event from a viral or bacterial vector into the mitochondrial genome of Nephtys sp. Our findings hold implications for understanding mechanisms, constraints, and selective pressures that account for patterns of animal mitochondrial genome evolution.

Show MeSH
Related in: MedlinePlus