Molecular evolution of angiosperm mitochondrial introns and exons

Area of Science:

• Molecular Evolution
• Plant Genomics
• Mitochondrial DNA

Background:

• Understanding evolutionary rates in plant organelles is crucial for phylogenetic and population genetics.
• Comparative analysis of coding and non-coding regions provides insights into selective pressures.
• Gene transfer between organelles and the nucleus can alter evolutionary trajectories.

Purpose of the Study:

• To compare evolutionary rates (substitutions and indels) between plant mitochondrial exons and introns.
• To investigate factors influencing rate heterogeneity across mitochondrial genes and taxa.
• To assess the evolutionary impact of nuclear transfer on mitochondrial genes.

Main Methods:

• Estimation of substitutions per site for 15 protein-coding genes and six introns in plant mitochondria.
• Analysis of insertions-deletions (indels) per site in introns.
• Relative rate tests and assessment of intra-gene homogeneity across taxa and paralogs.

Main Results:

• Gene-to-gene substitution rate differences were higher for nonsynonymous than synonymous sites.
• Some mitochondrial genes evolve as rapidly as chloroplast genes; woody taxa show slower evolution than annuals for coxI.
• Introns exhibit less constraint than exons, with similar substitution rates to exonic synonymous sites; nuclear-transferred genes show accelerated substitution rates.

Conclusions:

• Plant mitochondrial gene evolution is influenced by selection, generation time, population size, and speciation rates.
• Introns are under weaker evolutionary constraint than exons, but exhibit strong substitution-indel correlations.
• Nuclear transfer of mitochondrial genes leads to accelerated evolution, likely due to altered mutation rates.