Extensive and evolutionarily persistent mitochondrial tRNA editing in Velvet Worms (phylum Onychophora)

Area of Science:

• Mitochondrial genomics
• Molecular evolution
• RNA editing

Background:

• Mitochondrial genomes of onychophorans (velvet worms) exhibit unusual transfer RNA (tRNA) gene content, with conflicting reports of gene absence versus severe reduction.
• This discrepancy necessitates a detailed investigation into the structure and processing of these tRNA genes.

Purpose of the Study:

• To resolve the discrepancy regarding tRNA gene presence and structure in onychophoran mitochondrial genomes.
• To elucidate the mechanisms and evolutionary implications of tRNA editing in these organisms.

Main Methods:

• Determined complete mitochondrial DNA (mtDNA) sequences for Oroperipatus sp. and Peripatoides sympatrica.
• Sequenced cDNA for multiple tRNA molecules from both species to assess editing extent.
• Analyzed tRNA structures and compared editing patterns between species.

Main Results:

• Confirmed that onychophoran mitochondrial tRNA genes are highly reduced, encoding truncated molecules.
• Demonstrated extensive tRNA editing, with up to 34 nucleotides added in Oroperipatus sp. to restore functional tRNA structures.
• Identified distinct editing mechanisms for different tRNA regions, suggesting template-independent and -dependent processes.
• Observed conservation of extreme tRNA editing across extant onychophoran families, indicating long-term evolutionary stability.

Conclusions:

• Onychophoran mitochondrial tRNA genes undergo significant post-transcriptional editing to restore function, resolving previous discrepancies in gene content.
• The editing process involves both template-independent and -dependent mechanisms for rebuilding tRNA structures.
• This extreme tRNA editing is an ancient, conserved trait in onychophorans and may be present in related arthropod groups.