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A close phylogenetic relationship between Sipuncula and Annelida evidenced from the complete mitochondrial genome sequence of Phascolosoma esculenta.

Shen X, Ma X, Ren J, Zhao F - BMC Genomics (2009)

Bottom Line: It shares many more similar features with the four known annelid and one echiuran mtDNAs.Firstly, sipunculans and annelids share quite similar gene order in the mitochondrial genome, with all 37 genes located on the same strand; secondly, phylogenetic analyses based on the concatenated protein sequences also strongly support the sipunculan + annelid clade (including echiurans and pogonophorans).Hence annelid "key-characters" including segmentation may be more labile than previously assumed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Jiangsu Key Laboratory of Marine Biotechnology/College of Marine Science, Huaihai Institute of Technology, Lianyungang 222005, PR China. shenthin@163.com

ABSTRACT

Background: There are many advantages to the application of complete mitochondrial (mt) genomes in the accurate reconstruction of phylogenetic relationships in Metazoa. Although over one thousand metazoan genomes have been sequenced, the taxonomic sampling is highly biased, left with many phyla without a single representative of complete mitochondrial genome. Sipuncula (peanut worms or star worms) is a small taxon of worm-like marine organisms with an uncertain phylogenetic position. In this report, we present the mitochondrial genome sequence of Phascolosoma esculenta, the first complete mitochondrial genome of the phylum.

Results: The mitochondrial genome of P.esculenta is 15,494 bp in length. The coding strand consists of 32.1% A, 21.5% C, 13.0% G, and 33.4% T bases (AT = 65.5%; AT skew = -0.019; GC skew = -0.248). It contains thirteen protein-coding genes (PCGs) with 3,709 codons in total, twenty-two transfer RNA genes, two ribosomal RNA genes and a non-coding AT-rich region (AT = 74.2%). All of the 37 identified genes are transcribed from the same DNA strand. Compared with the typical set of metazoan mt genomes, sipunculid lacks trnR but has an additional trnM. Maximum Likelihood and Bayesian analyses of the protein sequences show that Myzostomida, Sipuncula and Annelida (including echiurans and pogonophorans) form a monophyletic group, which supports a closer relationship between Sipuncula and Annelida than with Mollusca, Brachiopoda, and some other lophotrochozoan groups.

Conclusion: This is the first report of a complete mitochondrial genome as a representative within the phylum Sipuncula. It shares many more similar features with the four known annelid and one echiuran mtDNAs. Firstly, sipunculans and annelids share quite similar gene order in the mitochondrial genome, with all 37 genes located on the same strand; secondly, phylogenetic analyses based on the concatenated protein sequences also strongly support the sipunculan + annelid clade (including echiurans and pogonophorans). Hence annelid "key-characters" including segmentation may be more labile than previously assumed.

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Gene map of mitochondrial genome of the P. esculenta (Sipuncula: Phascolosomatidea). All thirteen protein-coding, two ribosomal RNA and twenty-two transfer RNA genes are encoded on the same strand. Transfer RNA genes are designated by single-letter amino acid codes.
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Figure 1: Gene map of mitochondrial genome of the P. esculenta (Sipuncula: Phascolosomatidea). All thirteen protein-coding, two ribosomal RNA and twenty-two transfer RNA genes are encoded on the same strand. Transfer RNA genes are designated by single-letter amino acid codes.

Mentions: The mitochondrial genome of P. esculenta is 15,494 bp in length, and encodes a set of 37 metazoan genes (thirteen protein-coding, two ribosomal RNA, and twenty-two transfer RNA genes) (Figure 1; Table 1). The overall A+T content of P.esculenta (65.5%) is higher than that of the mitochondrial genomes from the Annelida/Echiura group except for one polychaete Clymenella torquata (67.2%) [see additional file 1]. The entire P.esculenta mtDNA sequence has been deposited in GenBank with accession number EF583817.


A close phylogenetic relationship between Sipuncula and Annelida evidenced from the complete mitochondrial genome sequence of Phascolosoma esculenta.

Shen X, Ma X, Ren J, Zhao F - BMC Genomics (2009)

Gene map of mitochondrial genome of the P. esculenta (Sipuncula: Phascolosomatidea). All thirteen protein-coding, two ribosomal RNA and twenty-two transfer RNA genes are encoded on the same strand. Transfer RNA genes are designated by single-letter amino acid codes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2667193&req=5

Figure 1: Gene map of mitochondrial genome of the P. esculenta (Sipuncula: Phascolosomatidea). All thirteen protein-coding, two ribosomal RNA and twenty-two transfer RNA genes are encoded on the same strand. Transfer RNA genes are designated by single-letter amino acid codes.
Mentions: The mitochondrial genome of P. esculenta is 15,494 bp in length, and encodes a set of 37 metazoan genes (thirteen protein-coding, two ribosomal RNA, and twenty-two transfer RNA genes) (Figure 1; Table 1). The overall A+T content of P.esculenta (65.5%) is higher than that of the mitochondrial genomes from the Annelida/Echiura group except for one polychaete Clymenella torquata (67.2%) [see additional file 1]. The entire P.esculenta mtDNA sequence has been deposited in GenBank with accession number EF583817.

Bottom Line: It shares many more similar features with the four known annelid and one echiuran mtDNAs.Firstly, sipunculans and annelids share quite similar gene order in the mitochondrial genome, with all 37 genes located on the same strand; secondly, phylogenetic analyses based on the concatenated protein sequences also strongly support the sipunculan + annelid clade (including echiurans and pogonophorans).Hence annelid "key-characters" including segmentation may be more labile than previously assumed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Jiangsu Key Laboratory of Marine Biotechnology/College of Marine Science, Huaihai Institute of Technology, Lianyungang 222005, PR China. shenthin@163.com

ABSTRACT

Background: There are many advantages to the application of complete mitochondrial (mt) genomes in the accurate reconstruction of phylogenetic relationships in Metazoa. Although over one thousand metazoan genomes have been sequenced, the taxonomic sampling is highly biased, left with many phyla without a single representative of complete mitochondrial genome. Sipuncula (peanut worms or star worms) is a small taxon of worm-like marine organisms with an uncertain phylogenetic position. In this report, we present the mitochondrial genome sequence of Phascolosoma esculenta, the first complete mitochondrial genome of the phylum.

Results: The mitochondrial genome of P.esculenta is 15,494 bp in length. The coding strand consists of 32.1% A, 21.5% C, 13.0% G, and 33.4% T bases (AT = 65.5%; AT skew = -0.019; GC skew = -0.248). It contains thirteen protein-coding genes (PCGs) with 3,709 codons in total, twenty-two transfer RNA genes, two ribosomal RNA genes and a non-coding AT-rich region (AT = 74.2%). All of the 37 identified genes are transcribed from the same DNA strand. Compared with the typical set of metazoan mt genomes, sipunculid lacks trnR but has an additional trnM. Maximum Likelihood and Bayesian analyses of the protein sequences show that Myzostomida, Sipuncula and Annelida (including echiurans and pogonophorans) form a monophyletic group, which supports a closer relationship between Sipuncula and Annelida than with Mollusca, Brachiopoda, and some other lophotrochozoan groups.

Conclusion: This is the first report of a complete mitochondrial genome as a representative within the phylum Sipuncula. It shares many more similar features with the four known annelid and one echiuran mtDNAs. Firstly, sipunculans and annelids share quite similar gene order in the mitochondrial genome, with all 37 genes located on the same strand; secondly, phylogenetic analyses based on the concatenated protein sequences also strongly support the sipunculan + annelid clade (including echiurans and pogonophorans). Hence annelid "key-characters" including segmentation may be more labile than previously assumed.

Show MeSH