Mitochondrial DNAs provide insight into trypanosome phylogeny and molecular evolution
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RESEARCH ARTICLE
Open Access
Mitochondrial DNAs provide insight into trypanosome phylogeny and molecular evolution C. Kay*, T. A. Williams and W. Gibson
Abstract Background: Trypanosomes are single-celled eukaryotic parasites characterised by the unique biology of their mitochondrial DNA. African livestock trypanosomes impose a major burden on agriculture across sub-Saharan Africa, but are poorly understood compared to those that cause sleeping sickness and Chagas disease in humans. Here we explore the potential of the maxicircle, a component of trypanosome mitochondrial DNA to study the evolutionary history of trypanosomes. Results: We used long-read sequencing to completely assemble maxicircle mitochondrial DNA from four previously uncharacterized African trypanosomes, and leveraged these assemblies to scaffold and assemble a further 103 trypanosome maxicircle gene coding regions from published short-read data. While synteny was largely conserved, there were repeated, independent losses of Complex I genes. Comparison of pre-edited and non-edited genes revealed the impact of RNA editing on nucleotide composition, with non-edited genes approaching the limits of GC loss. African tsetse-transmitted trypanosomes showed high levels of RNA editing compared to other trypanosomes. The gene coding regions of maxicircle mitochondrial DNAs were used to construct time-resolved phylogenetic trees, revealing deep divergence events among isolates of the pathogens Trypanosoma brucei and T. congolense. Conclusions: Our data represents a new resource for experimental and evolutionary analyses of trypanosome phylogeny, molecular evolution and function. Molecular clock analyses yielded a timescale for trypanosome evolution congruent with major biogeographical events in Africa and revealed the recent emergence of Trypanosoma brucei gambiense and T. equiperdum, major human and animal pathogens. Keywords: Trypanosome, Kinetoplast, Maxicircle, Mitochondrial DNA, Phylogeny, RNA editing Background Trypanosomes are a group of single-celled eukaryotic flagellates, including important pathogens of humans and their livestock (Trypanosoma and Leishmania), plants (Phytomonas) and insects (Crithidia). A distinctive feature of trypanosomes is the compartmentalization of the mitochondrial DNA into an organelle located at the proximal end of the flagellum, the kinetoplast, which contains a network of interlocked circular *Correspondence: [email protected] School of Biological Sciences, University of Bristol, Bristol, UK
DNAs of two types: maxicircles which are equivalent to the mitochondrial genome of other eukaryotes, and minicircles that encode guide RNAs (gRNAs) used to edit the maxicircle transcripts [1, 2]. Thus both miniand maxicircles are essential for expression of mitochondrial genes. In trypanosomes, mitochondrial transcripts are edited by the insertion or deletion of uridine residues at positions demarcated by gRNAs to yield mRNAs that can be correctly translated [3–5]. Why this energetically costly and potentially error pron
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