De Novo Mutation Rate Variation and Its Determinants in Chlamydomonas

Area of Science:

• Evolutionary biology
• Genetics
• Molecular biology

Background:

• De novo mutations are crucial for evolution by generating genetic variation.
• Studying mutation rates and spectra across species is challenging, limiting our understanding of their evolution.
• Previous research has primarily focused on model organisms, leaving gaps in knowledge for closely related species.

Purpose of the Study:

• To investigate de novo mutation rates and spectra in the unicellular green alga Chlamydomonas incerta.
• To compare mutation patterns between C. incerta and its close relative, Chlamydomonas reinhardtii.
• To identify genomic factors influencing mutation rate variation.

Main Methods:

• A mutation accumulation experiment was conducted on Chlamydomonas incerta.
• Whole-genome sequencing was used to analyze de novo mutations.
• Comparative genomic analyses were performed between C. incerta and C. reinhardtii.

Main Results:

• The median single nucleotide mutation rate in C. incerta was estimated at 7.6 × 10-10, with significant variability among lines.
• A strong positive correlation was observed between single nucleotide mutation rates and insertion/deletion mutation rates.
• Genomic factors like sequence context and complexity were found to be more influential than GC content on mutation rate variation, similar to C. reinhardtii.
• The single nucleotide mutation spectrum differed markedly between the two species, except for a high C→T bias in C. incerta.

Conclusions:

• Similar genomic and biological factors likely contribute to comparable mutation rates in C. incerta and C. reinhardtii.
• Despite similar mutation rates, the mutation spectrum shows considerable divergence between these closely related species.
• Sequence context and complexity are key drivers of mutation rate variation, more so than GC content.