RT Journal Article
SR Electronic
T1 The mitochondrial genomes of the acoelomorph worms <em>Paratomella rubra</em> and <em>Isodiametra pulchra</em>
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 103556
DO 10.1101/103556
A1 Robertson, Helen E
A1 Lapraz, François
A1 Egger, Bernhard
A1 Telford, Maximilian J
A1 Schiffer, Philipp H.
YR 2017
UL http://biorxiv.org/content/early/2017/01/26/103556.abstract
AB Acoels are small, ubiquitous, but understudied, marine worms with a very simple body plan. Their internal phylogeny is still in parts unresolved, and the position of their proposed phylum Xenacoelomorpha (Xenoturbella+Acoela) is still debated.Here we describe mitochondrial genome sequences from two acoel species: Paratomella rubra and Isodiametra pulchra. The 14,954 nucleotide-long P. rubra sequence is typical for metazoans in size and gene content. The larger I. pulchra mitochondrial genome contains both ribosomal genes, 21 tRNAs, but only 11 protein-coding genes. We find evidence suggesting a duplicated sequence in the I. pulchra mitochondrial genome.Mitochondrial sequences for both P. rubra and I. pulchra have a unique genome organisation in comparison to other published metazoan mitochondrial genomes. We found a large degree of protein-coding gene and tRNA overlap in P. rubra, with little non-coding sequence making the genome compact. Conversely, the I. pulchra mitochondrial genome has many long non-coding sequences between genes, likely driving the genome size expansion. Phylogenetic trees inferred from concatenated alignments of mitochondrial genes grouped the fast-evolving Acoela and Tunicata, almost certainly due to the systematic error of long branch attraction: a reconstruction artefact that is probably compounded by the fast substitution rate of mitochondrial genes in this taxon.