engleski

Insights on the mitochondrial genome of appendicularians

<i>Oikopleura dioica</i> (Appendicularia) is a model organism to understand the evolution of chordates. Although its nuclear genome has been sequenced, its mitochondrial (mt) genome has not been determined, probably because of their fast evolutionary rate and extensive RNA editing. We sequenced cDNA of the cox1 gene and nuclear genomes (using Illumina) from <i>O. dioica</i> and <i>Fritillaria pellucida</i>. Mapping the resulting DNA reads onto the cox1 cDNA sequences, we confirmed the previously-published observation that, at DNA level, long poly-T stretches interrupt the mt ORFs, hampering their identification. In addition, we noticed that mitogenomic poly-T correspond at RNA level to TTTTTT (6T) regions in <i>O. dioica</i> but to shorter TTTT (4T) regions in <i>F. pellucida</i>, leading to hypothesize species-specific RNA editings by deletion. Remarkably, different editing sites were observed between Mediterranean and Japanese populations of <i>O. dioica</i> suggesting a rapid evolution of these sites.While tRNAs usually punctuate the protein-coding genes in chordate mt genome, only one tRNA, tRNAmet, was identified among <i>O. dioica</i> mt contigs assembled from published cDNA reads. To test if mt tRNAs could have been lost, we searched the genomic assembly for the presence of mt aminoacyl tRNA synthetase (aaRS) genes, which encode the proteins responsible for the aminoacylation of its cognate tRNA. No specific mt aaRS genes were found in the nuclear genome assembly of O. dioica except for mt-MetRS, which catalyzes the mt-tRNAMet aminoacylation. This suggests that the mt genome of <i>O. dioica</i> encodes only the single tRNAMet.

Appendicularia ; mtDNA ; RNA editing ; Fritillaria pellucida ; Oikopleura dioica

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