Mitogenomics Reveals a Novel Genetic Code in Hemichordata.

Area of Science:

• Mitochondrial genomics
• Evolutionary biology
• Molecular genetics

Background:

• The genetic code's universality is challenged by observed codon reassignments.
• Hemichordata (Enteropneusta and Pterobranchia) is crucial for understanding deuterostome evolution, but their mitochondrial genomes are underrepresented.
• Limited sequencing of hemichordate mitochondrial genomes hinders understanding of mitochondrial genome evolution within Deuterostomia.

Purpose of the Study:

• To investigate mitochondrial genome evolution in Hemichordata by sequencing new genomes and transcriptomes.
• To analyze codon reassignment and genetic code variations within hemichordate lineages.
• To clarify the phylogenetic relationships and evolutionary dynamics of mitochondrial genes and genetic codes in Hemichordata.

Main Methods:

• Sequencing of four mitochondrial genomes and two transcriptomes from hemichordates.
• Comparative analysis of newly sequenced data with publically available hemichordate genomic and transcriptomic data.
• Phylogenetic analyses to infer evolutionary relationships and genetic code evolution.

Main Results:

• Identified UAA encoding Tyrosine instead of a Stop codon in the Cephalodiscidae (pterobranch) lineage.
• Predicted AAA encoding Lysine in both pterobranch and enteropneust mitochondrial genomes, contradicting the assumed shared code with echinoderms (AAA encoding Asparagine).
• Proposed a new mitochondrial genetic code for Cephalodiscus and revised codes for enteropneusts, alongside phylogenetic insights including the unique placement of Stereobalanus.

Conclusions:

• Mitochondrial gene order and genetic codes in Hemichordata exhibit greater evolutionary dynamism than previously recognized.
• The findings necessitate a re-evaluation of the mitochondrial genetic code in hemichordates and provide critical insights into deuterostome mitochondrial genome evolution.
• This study expands the known diversity of genetic codes and highlights the importance of comprehensive genomic data for evolutionary studies.