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Complete mitochondrial genome of Cheilio inermis (Labriformes, Labridae).

ABSTRACT: In the present report, we describe the first sequencing and assembly of the complete mitochondrial genome of Cheilio inermis. The mitochondrial genome of C. inermis, with 16,494 bp in length, has the typical vertebrate mitochondrial gene arrangement. It contains 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a control region. All the tRNA genes typically formed a cloverleaf secondary structure. Phylogenetic analysis using mitochondrial genomes of 11 species showed that C. inermis formed monophyletic group with other Labridae species.

SUBMITTER: Song HY

PROVIDER: S-EPMC7800952 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundParatetraonchoides inermis (Monogenea: Tetraonchoididae) is a flatworm parasitising the gills of uranoscopid fishes. Its morphological characteristics are ambiguous, and molecular data have never been used to study its phylogenetic relationships, which makes its taxonomic classification controversial. Also, several decades of unsuccessful attempts to resolve the relationships within the Monogenea present a strong indication that morphological datasets may not be robust enough to be used to infer evolutionary histories. As the use of molecular data is currently severely limited by their scarcity, we have sequenced and characterized the complete mitochondrial (mt) genome of P. inermis. To investigate its phylogenetic position, we performed phylogenetic analyses using Bayesian inference and maximum likelihood approaches using concatenated amino acid sequences of all 12 protein-coding genes on a dataset containing all available monogenean mt genomes.ResultsThe circular mt genome of P. inermis (14,654 bp) contains the standard 36 genes: 22 tRNAs, two rRNAs, 12 protein-encoding genes (PCGs; Atp8 is missing) and a major non-coding region (mNCR). All genes are transcribed from the same strand. The A + T content of the whole genome (82.6%), as well as its elements, is the highest reported among the monogeneans thus far. Three tRNA-like cloverleaf structures were found in mNCR. Several results of the phylogenomic analysis are in disagreement with previously proposed relationships: instead of being closely related to the Gyrodactylidea, Tetraonchidea exhibit a phylogenetic affinity with the Dactylogyridea + Capsalidea clade; and the order Capsalidea is neither basal within the subclass Monopisthocotylea, nor groups with the Gyrodactylidea, but instead forms a sister clade with the Dactylogyridea. The mt genome of P. inermis exhibits a unique gene order, with an extensive reorganization of tRNAs. Monogenea exhibit exceptional gene order plasticity within the Neodermata.ConclusionsThis study shows that gene order within monopisthocotylid mt genomes is evolving at uneven rates, which creates misleading evolutionary signals. Furthermore, our results indicate that all previous attempts to resolve the evolutionary history of the Monogenea may have produced at least partially erroneous relationships. This further corroborates the necessity to generate more molecular data for this group of parasitic animals.

Project description:The complete sequence of honeybee (Apis mellifera) mitochondrial DNA is reported being 16,343 bp long in the strain sequenced. Relative to their positions in the Drosophila map, 11 of the tRNA genes are in altered positions, but the other genes and regions are in the same relative positions. Comparisons of the predicted protein sequences indicate that the honeybee mitochondrial genetic code is the same as that for Drosophila; but the anticodons of two tRNAs differ between these two insects. The base composition shows extreme bias, being 84.9% AT (cf. 78.6% in Drosophila yakuba). In protein-encoding genes, the AT bias is strongest at the third codon positions (which in some cases lack guanines altogether), and least in second codon positions. Multiple stepwise regression analysis of the predicted products of the protein-encoding genes shows a significant association between the numbers of occurrences of amino acids and %T in codon family, but not with the number of codons per codon family or other parameters associated with codon family base composition. Differences in amino acid abundances are apparent between the predicted Apis and Drosophila proteins, with a relative abundance in the Apis proteins of lysine and a relative deficiency of alanine. Drosophila alanine residues are as often replaced by serine as conserved in Apis. The differences in abundances between Drosophila and Apis are associated with %AT in the codon families, and the degree of divergence in amino acid composition between proteins correlates with the divergence in %AT at the second codon positions. Overall, transversions are about twice as abundant as transitions when comparing Drosophila and Apis protein-encoding genes, but this ratio varies between codon positions. Marked excesses of transitions over chance expectation are seen for the third positions of protein-coding genes and for the gene for the small subunit of ribosomal RNA. For the third codon positions the excess of transitions is adequately explained as due to the restriction of observable substitutions to transitions for conserved amino acids with two-codon families; the excess of transitions over expectation for the small ribosomal subunit suggests that the conservation of nucleotide size is favored by selection.

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Complete mitochondrial genome of Cheilio inermis (Labriformes, Labridae).

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