MITOCHONDRIAL GENOME EVOLUTION IN THE DEEP-BRANCHING HETEROLOBOSEIDS AMOEBA ‘BB2’ AND PHARYNGOMONAS KIRBYI
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Studies of mitochondrial genomes from diverse eukaryotes provide insights into how mitochondria evolved. Previous research revealed several evolutionarily interesting mitochondrial genomes in the taxon Discoba (Excavata), including the most bacteria-like mitochondrial genomes of Jakobida and extensively fragmented mitochondrial genomes of Euglenozoa. I characterized the mitochondrial genomes of amoeba BB2 and Pharyngomonas kirbyi, which represent deep branches within Heterolobosea, the third main group of Discoba. Using phylogenomic analyses, I showed that BB2 and P. kirbyi are sister taxa at the very base of Heterolobosea. I assembled mitochondrial genomes of BB2 (119 kbp) and P. kirbyi (75 kbp) encoding 45 and 48 putative protein-coding genes, respectively. Interestingly, BB2 mitochondrial genes were extensively fragmented by frame-shifts. Comparative analysis of genomic and transcriptomic data revealed that mitochondrial transcripts of BB2 are heavily edited by mononucleotide insertions to produce functional RNAs. Bioinformatics analyses suggested that this RNA editing is very accurate and efficient, and possibly co-transcriptional.