Compositional Analysis of Flatworm Genomes Shows Strong Codon Usage Biases Across All Classes.

Area of Science:

• Genomics
• Molecular Evolution
• Bioinformatics

Background:

• The phylum Platyhelminthes encompasses diverse species with varied lifestyles.
• Understanding the evolutionary pressures shaping their genomes is crucial for comparative biology.

Purpose of the Study:

• To conduct a comparative genome-wide analysis of 22 Platyhelminthes species.
• To investigate changes in GC content, codon usage, and amino acid usage.
• To elucidate the evolutionary forces driving coding strategies in flatworms.

Main Methods:

• Comparative genome-wide analysis of 22 representative Platyhelminthes species.
• Selection of 700 conserved orthologous genes across all species.
• Measurement of GC content, codon usage, and amino acid usage at orthologous positions.
• Hierarchical clustering of codon usage data and phylogenetic analysis.
• Analysis of synonymous and non-synonymous substitutions.

Main Results:

• GC content at the 3rd codon position allowed discrimination between freshwater turbellarians, Cestodes, and Trematodes.
• Codon usage clustering deviated significantly from the established phylogenetic tree.
• Synonymous codon usage bias was pronounced in extreme GC-poor (Schistosomes) and GC-rich (M. lignano) genomes.
• This bias influenced amino acid usage, correlating with GC content trends and non-synonymous substitutions.

Conclusions:

• A two-hit mechanism involving both mutation and selection drives the diverse coding strategies observed in flatworms.
• Synonymous codon usage bias is a significant factor in shaping protein evolution within this phylum.
• Comparative genomic analysis provides insights into the molecular evolution of Platyhelminthes.