MBE Advance Access originally published online on May 28, 2007
Molecular Biology and Evolution 2007 24(8):1783-1791; doi:10.1093/molbev/msm106
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Research Articles |
Variation in Mutation Rate and Polymorphism Among Mitochondrial Genes of Silene vulgaris
* Department of Biology, University of Virginia
Division of Biological Sciences, University of Montana
Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden
E-mail: camille.barr{at}mso.umt.edu.
Accepted for publication May 11, 2007.
The prevailing wisdom of the plant mitochondrial genome is that it has very low substitution rates, thus it is generally assumed that nucleotide diversity within species will also be low. However, recent evidence suggests plant mitochondrial genes may harbor variable and sometimes high levels of within-species polymorphism, a result attributed to variance in the influence of selection. However, insufficient attention has been paid to the effect of among-gene variation in mutation rate on varying levels of polymorphism across loci. We measured levels of polymorphism in seven mitochondrial gene regions across a geographically wide sample of the plant Silene vulgaris to investigate whether individual mitochondrial genes accumulate polymorphisms equally. We found that genes vary significantly in polymorphism. Tests based on coalescence theory show that the genes vary significantly in their scaled mutation rate, which, in the absence of differences among genes in effective population size, suggests these genes vary in their underlying mutation rate. Further evidence that among-gene variance in polymorphism is due to variation in the underlying mutation rate comes from a significant positive relationship between the number of segregating sites and silent site divergence from an outgroup. Contrary to recent studies, we found unconvincing evidence of recombination in the mitochondrial genome, and generally confirm the standard model of plant mitochondria characterized by low substitution rates and no recombination. We also show no evidence of significant variation in the strength or direction of selection among genes; this result may be expected if there is no recombination. The present study provides some of the most thorough data on plant mitochondrial polymorphism, and provides compelling evidence for mutation rate variation among genes. The study also demonstrates the difficulty in establishing a null model of mitochondrial genome polymorphism, and thus the difficulty, in the absence of a comparative approach, in testing the assumption that low substitution rates in plant mitochondria lead to low polymorphism.
Key Words: plant mitochondria • polymorphism • mutation rate • recombination • Silene vulgaris
Spencer V. Muse, Associate Editor
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  D. E. McCauley and M. F. Bailey Recent advances in the study of gynodioecy: the interface of theory and empiricism Ann. Bot., September 1, 2009; 104(4): 611 - 620. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. A. Pearl, M. E. Welch, and D. E. McCauley Mitochondrial Heteroplasmy and Paternal Leakage in Natural Populations of Silene vulgaris, a Gynodioecious Plant Mol. Biol. Evol., March 1, 2009; 26(3): 537 - 545. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Touzet and L. F. Delph The Effect of Breeding System on Polymorphism in Mitochondrial Genes of Silene Genetics, February 1, 2009; 181(2): 631 - 644. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. B. Sloan, C. M. Barr, M. S. Olson, S. R. Keller, and D. R. Taylor Evolutionary Rate Variation at Multiple Levels of Biological Organization in Plant Mitochondrial DNA Mol. Biol. Evol., February 1, 2008; 25(2): 243 - 246. [Abstract] [Full Text] [PDF]
|
|