Context-Dependent Mutation Dynamics, Not Selection, Explains the Codon Usage Bias of Most Angiosperm Chloroplast...

Area of Science:

• Molecular Biology
• Evolutionary Genetics
• Bioinformatics

Background:

• Codon usage in angiosperm chloroplast genes is debated, with two main hypotheses: significant selection versus mutation bias and drift.
• Previous studies noted deviations from neutral expectations, suggesting selection's role.

Purpose of the Study:

• To investigate the extent to which natural selection influences codon usage in angiosperm chloroplast genes.
• To differentiate between selection and mutation bias as drivers of codon usage patterns.

Main Methods:

• Analysis of mutation dynamics influenced by neighboring base composition.
• Prediction of neutral codon usage biases based on observed mutation properties.
• Comparison of predicted neutral biases with observed codon usage patterns.

Main Results:

• Compositional biases are expected to vary significantly across different sites due to context-dependent mutation dynamics, even without selection.
• Observed codon usage deviations from naive expectations are explained by these context-dependent mutational dynamics.
• A strong match between observed and expected codon usage was found when context effects were considered, except for the psbA gene.

Conclusions:

• Selection is not a widespread factor influencing codon usage in angiosperm chloroplast genes.
• Mutation bias and genetic drift are the dominant forces shaping codon usage.
• Accurate models of context-dependent mutational dynamics are crucial for understanding codon usage evolution.