The complete nucleotide sequence of the mitochondrial genome (mitogenome) of Geisha distinctissima (Hemiptera: Flatidae) has been determined in this study. The genome is a circular molecule of 15,971 bp with a total A+T content of 75.1%. The gene content, order, and structure are consistent with the Drosophila yakuba genome structure and the hypothesized ancestral arthropod genome arrangement. All 13 protein-coding genes are observed to have a putative, inframe ATR methionine or ATT isoleucine codons as start signals. Canonical TAA and TAG termination codons are found in nine protein-coding genes, and the remaining four (cox1, atp6, cox3, and nad4) have incomplete termination codons. The anticodons of all transfer RNA (tRNAs) are identical to those observed in D. yakuba and Philaenus spumarius, and can be folded in the form of a typical clover-leaf structure except for tRNA(Ser(AGN)). The major non-coding region (the A+T-rich region or putative control region) between the small ribosomal subunit and the tRNA(Ile) gene includes two sets of repeat regions. The first repeat region consists of a direct 152-bp repetitive unit located near the srRNA gene end, and the second repeat region is composed of a direct repeat unit of 19 bp located toward tRNA(Ile) gene. Comparisons of gene variability across the order suggest that the gene content and arrangement of G. distinctissima mitogenome are similar to other hemipteran insects.
Molecular surveys are leading to the discovery of many new cryptic species of marine algae. This is particularly true for red algal intertidal species, which exhibit a high degree of morphological convergence. DNA sequencing of recent collections of Gelidium along the coast of California, USA, identified two morphologically similar entities that differed in DNA sequence from existing species. To characterize the two new species of Gelidium and to determine their evolutionary relationships to other known taxa, phylogenomic, multigene analyses, and morphological observations were performed. Three complete mitogenomes and five plastid genomes were deciphered, including those from the new species candidates and the type materials of two closely related congeners. The mitogenomes contained 45 genes and had similar lengths (24,963-24,964 bp). The plastid genomes contained 232 genes and were roughly similar in size (175,499-177,099 bp). The organellar genomes showed a high level of gene synteny. The two Gelidium species are diminutive, turf-forming, and superficially resemble several long established species from the Pacific Ocean. The phylogenomic analysis, multigene phylogeny, and morphological evidence confirms the recognition and naming of two new species, describe herein as G. gabrielsonii and G. kathyanniae. On the basis of the monophyly of G. coulteri, G. gabrielsonii, G. galapagense, and G. kathyanniae, we suggest that this lineage likely evolved in California. Organellar genomes provide a powerful tool for discovering cryptic intertidal species and they continue to improve our understanding of the evolutionary biology of red algae and the systematics of the Gelidiales.
External segmentation and internal proglottization are important evolutionary characters of the Eucestoda. The monozoic caryophyllideans are considered the earliest diverging eucestodes based on partial mitochondrial genes and nuclear rDNA sequences, yet, there are currently no complete mitogenomes available. We have therefore sequenced the complete mitogenomes of three caryophyllideans, as well as the polyzoic Schyzocotyle acheilognathi, explored the phylogenetic relationships of eucestodes and compared the gene arrangements between unsegmented and segmented cestodes.
The circular mitogenome of Atractolytocestus huronensis was 15,130 bp, the longest sequence of all the available cestodes, 14,620 bp for Khawia sinensis, 14,011 bp for Breviscolex orientalis and 14,046 bp for Schyzocotyle acheilognathi. The A-T content of the three caryophyllideans was found to be lower than any other published mitogenome. Highly repetitive regions were detected among the non-coding regions (NCRs) of the four cestode species. The evolutionary relationship determined between the five orders (Caryophyllidea, Diphyllobothriidea, Bothriocephalidea, Proteocephalidea and Cyclophyllidea) is consistent with that expected from morphology and the large fragments of mtDNA when reconstructed using all 36 genes. Examination of the 54 mitogenomes from these five orders, revealed a unique arrangement for each order except for the Cyclophyllidea which had two types that were identical to that of the Diphyllobothriidea and the Proteocephalidea. When comparing gene order between the unsegmented and segmented cestodes, the segmented cestodes were found to have the lower similarities due to a long distance transposition event. All rearrangement events between the four arrangement categories took place at the junction of rrnS-tRNA Arg (P1) where NCRs are common.
Highly repetitive regions are detected among NCRs of the four cestode species. A long distance transposition event is inferred between the unsegmented and segmented cestodes. Gene arrangements of Taeniidae and the rest of the families in the Cyclophyllidea are found be identical to those of the sister order Proteocephalidea and the relatively basal order Diphyllobothriidea, respectively.
To investigate genetic mechanisms of high altitude adaptations of native mammals on the Tibetan Plateau, we compared mitochondrial sequences of the endangered Pantholops hodgsonii with its lowland distant relatives Ovis aries and Capra hircus, as well as other mammals. The complete mitochondrial genome of P. hodgsonii (16,498 bp) revealed a similar gene order as of other mammals. Because of tandem duplications, the control region of P. hodgsonii mitochondrial genome is shorter than those of O. aries and C. hircus, but longer than those of Bos species. Phylogenetic analysis based on alignments of the entire cytochrome b genes suggested that P. hodgsonii is more closely related to O. aries and C. hircus, rather than to species of the Antilopinae subfamily. The estimated divergence time between P. hodgsonii and O. aries is about 2.25 million years ago. Further analysis on natural selection indicated that the COXI (cytochrome c oxidase subunit I) gene was under positive selection in P. hodgsonii and Bos grunniens. Considering the same climates and environments shared by these two mammalian species, we proposed that the mitochondrial COXI gene is probably relevant for these native mammals to adapt the high altitude environment unique to the Tibetan Plateau.
The complete mitochondrial genome is greatly important for studies on genetic structure and phylogenetic relationship at various taxonomic levels. To obtain information about the evolutionary trends of mtDNA in the Ulvophyceae and also to gain insights into the phylogenetic relationships between ulvophytes and other chlorophytes, we determined the mtDNA sequence of Caulerpa lentillifera (sea grape) using de novo mitochondrial genome sequencing. The complete genomic DNA of C. lentillifera was circular and 209,034 bp in length, and it was the largest green-algal mitochondrial genome sequenced to date, with a low gene density of 65.2%, which is reminiscent of the "expanded" pattern of evolution exhibited by embryophyte mtDNAs. The C. lentillifera mtDNA consisted of a typical set of 17 protein-coding genes (PCGs), 20 transfer RNA (tRNA) genes, three ribosomal RNA (rRNA) genes, 42 putative open reading frames (ORFs) and 29 introns, which had homologs in green-algal mtDNAs displaying an "ancestral" or a "reduced-derived" pattern of evolution. The overall base composition of its mitochondrial genome was 24.19% for A, 24.94% for T, 25.80% for G, 25.07% for C and 50.87% for GC. The mitochondrial genome of C. lentillifera was characterized by numerous small intergenic regions and introns, which was clearly different from other green algae. With the exception of the NADH dehydrogenase subunit 6 (ND6), ND1, ATP and three tRNA genes (tRNA-His, tRNA-Thr and tRNA-Ala), all other mitochondrial genes were encoded on the heavy strand. All of the PCGs had ATG as their start codon and employed TAA, TGA or TAG as their termination codon. To gain insights into the evolutionary trends of mtDNA in the Ulvophyceae, we inferred the complete mtDNA sequence of C. lentillifera, an ulvophyte belonging to a distinct, early-diverging lineage. Taken together, our data offered useful information for the studies on phylogenetic hypotheses and phylogenetic relationships of C. lentillifera within the Chlorophyta.
We sequenced and annotated the complete mitochondrial genome (mitogenome) of Bactrocera diaphora (Diptera: Tephtitidae), which is an economically important pest in the southwest area of China, India, Sri Lanka, Vietnam and Malaysia. This mitogenome is 15 890 bp in length with an A + T content of 74.103%, and contains 37 typical animal mitochondrial genes that are arranged in the same order as that of the inferred ancestral insects. All protein-coding genes (PCGs) start with a typical ATN codon, except cox1 that begins with TCG. Ten PCGs stop with termination codon TAA or TAG, whereas cox1, nad1 and nad5 have single T-- as the incomplete stop codon. All of the transfer RNA genes present the typical clover leaf secondary structure except trnS1 (AGN) with a looping D-arm. The A + T-rich region is located between rrnS and trnI with a length of 946 bp, and contains a 20 bp poly-T stretch and 22 bp poly-A stretch. Except the control region, the longest intergenic spacer is located between trnR and trnN that is 94 bp long with an excessive high A + T content (95.74%) and a microsatellite-like region (TA)13.
The mitochondrial genomes of the genus Echinococcus have already been sequenced for most species and genotypes to reconstruct their phylogeny. However, two important taxa, E. felidis and E. canadensis G10 genotype (Fennoscandian cervid strain), were lacking in the published phylogeny. In this study, the phylogeny based on mitochondrial genome sequences was completed with these taxa. The present phylogeny highly supports the previous one, with an additional topology showing sister relationships between E. felidis and E. granulosus sensu stricto and between E. canadensis G10 and E. canadensis G6/G7 (closely related genotypes referred to as camel and pig strains, respectively). The latter relationship has a crucial implication for the species status of E. canadensis. The cervid strain is composed of two genotypes (G8 and G10), but the present phylogeny clearly suggests that they are paraphyletic. The paraphyly was also demonstrated by analysing the complete nucleotide sequences of mitochondrial cytochrome c oxidase subunit 1 (cox1) of E. canadensis genotypes from various localities. A haplotype network analysis using the short cox1 sequences from worldwide isolates clearly showed a close relatedness of G10 to G6/G7. Domestic and sylvatic life cycles based on the host specificity of E. canadensis strains have been important for epidemiological considerations. However, the taxonomic treatment of the strains as separate species or subspecies is invalid from a molecular cladistic viewpoint.
The complete nucleotide sequence of the mitochondrial genome of the white rhinoceros, Ceratotherium simum, was determined. The length of the reported sequence is 16,832 nucleotides. This length can vary, however, due to pronounced heteroplasmy caused by differing numbers of a repetitive motif (5'-CG-CATATACA-3') in the control region. The 16,832 nucleotide sequence presented here is the longest version of the molecule and contains 35 copies of this motif. Comparison between the complete mitochondrial sequences of the white and the Indian (Rhinoceros unicornis) rhinoceroses allowed an estimate of the date of the basal evolutionary divergence among extant rhinoceroses. The calculation suggested that this divergence took place approximately 27 million years before present.
The evolution of mitochondrial information processing pathways, including replication, transcription and translation, is characterized by the gradual replacement of mitochondrial-encoded proteins with nuclear-encoded counterparts of diverse evolutionary origins. Although the ancestral enzymes involved in mitochondrial transcription and replication have been replaced early in eukaryotic evolution, mitochondrial translation is still carried out by an apparatus largely inherited from the α-proteobacterial ancestor. However, variation in the complement of mitochondrial-encoded molecules involved in translation, including transfer RNAs (tRNAs), provides evidence for the ongoing evolution of mitochondrial protein synthesis. Here, we investigate the evolution of the mitochondrial translational machinery using recent genomic and transcriptomic data from animals that have experienced the loss of mt-tRNAs, including phyla Cnidaria and Ctenophora, as well as some representatives of all four classes of Porifera. We focus on four sets of mitochondrial enzymes that directly interact with tRNAs: Aminoacyl-tRNA synthetases, glutamyl-tRNA amidotransferase, tRNA(Ile) lysidine synthetase, and RNase P. Our results support the observation that the fate of nuclear-encoded mitochondrial proteins is influenced by the evolution of molecules encoded in mitochondrial DNA, but in a more complex manner than appreciated previously. The data also suggest that relaxed selection on mitochondrial translation rather than coevolution between mitochondrial and nuclear subunits is responsible for elevated rates of evolution in mitochondrial translational proteins.
The nucleotide sequence of the mitochondrial DNA (mtDNA) of the harbor seal, Phoca vitulina, was determined. The total length of the molecule was 16,826 bp. The organization of the coding regions of the molecule conforms with that of other mammals, but the control region is unusually long. A considerable portion of the control region is made up of short repeats with the motif GTACAC particularly frequent. The two rRNA genes and the 13 peptide-coding genes of the harbor seal, fin whale, cow, human, mouse, and rat were compared and the relationships between the different species assessed. At ordinal level the 12S rRNA gene and 7 out of the 13 peptide-coding genes yielded a congruent topological tree of the mtDNA relationship between the seal, cow, whale, human, and the rodents. In this tree the whale and the cow join first, and this clade is most closely related to the seal.