Loss of mitochondrial single stranded DNA-binding protein (mtSSB) gene is associated with mitochondrial genome fragmentation in Psocodea (bark lice, book lice, and parasitic lice).

BACKGROUND: Organelle genome fragmentation is a drastic large-scale chromosomal mutation. Why and how organelle genomes become fragmented is still poorly understood. Two previous studies based on whole genome comparison between human louse and fruit fly proposed that the loss of mtSSB gene (for mitochondrial single-stranded DNA-binding protein) might be associated with mitochondrial (mt) genome fragmentation. Whether this association is valid has not been investigated due to the lack of mt genome fragmentation data. RESULTS: We investigated this association by exploring the genomic and transcriptomic data of 198 species of parasitic lice, book lice, bark lice, and other closely related hemipteroid insects accumulated in the past few decades. We show that the loss of mtSSB gene is correlated significantly with mt genome fragmentation in bark lice, book lice, and parasitic lice (Psocodea). The absence of mtSSB is more frequent than expected in the species with fragmented mt genomes whereas the presence of mtSSB is more frequent than expected in the species with single-chromosome mt genome organization. Nevertheless, our results reject a cause-and-effect relationship between the loss of mtSSB and mt genome fragmentation because mtSSB is present in 11 species of parasitic lice and one book louse species that have fragmented mt genomes. CONCLUSIONS: The loss of mtSSB gene is correlated with mt genome fragmentation but is not the cause of mt genome fragmentation. Rather, it is plausible that fragmented mt genomes with multiple small-sized minichromosomes may make mtSSB gene and mtSSB protein less critical or unnecessary, leading to their loss eventually in the species with fragmented mt genomes.