A novel fragmented mitochondrial genome in the protist pathogen Toxoplasma gondii and related tissue coccidia

Mitochondrial genome content and structure vary widely across the eukaryotic tree of life with protists displaying extreme examples. Apicomplexan and dinoflagellate protists have evolved highly-reduced mitochondrial genome sequences, mtDNA, consisting of only 3 cytochrome genes and fragmented rRNA genes.

Here we report the independent evolution of fragmented cytochrome genes in Toxoplasma and related tissue coccidia and evolution of a novel genome architecture consisting minimally of 21 sequence blocks (SBs) that exist as non-random concatemers.

Single-molecule Nanopore reads consisting entirely of SB concatemers ranging from 1-23 kb reveal both whole and fragmented cytochrome genes. Full-length cytochrome transcripts including a divergent coxIII are detected. The topology of the mitochondrial genome remains an enigma. Analysis of a cob point mutation reveals that homoplasmy of SB’s is maintained.

Tissue coccidia are important pathogens of man and animals and the mitochondrion represents an important therapeutic target. Their mtDNA sequence has remained elusive until now.