MBE Advance Access published online on May 30, 2003
Molecular Biology and Evolution, doi:10.1093/molbev/msg122
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2003; all rights reserved
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1 Biochemistry and Molecular Biology, James Cook University, Townsville, Queensland, 4810
* To whom correspondence should be addressed. E-mail: m.vanoppen{at}aims.gov.au.
One characteristic of Indo-Pacific Acropora spp. is extremely high diversity in rDNA sequences at both the species and individual levels. In order to test the hypothesis that pseudogenes may contribute to this diversity, three kinds of analyses were conducted. First, for A. millepora (the species containing the most diverse suite of rDNA types), RT-PCR was used to determine which 5.8S rDNA types are expressed. Second, as previous studies have indicated that interspecific hybridization has occurred in the genus Acropora and silencing of rDNA loci via nucleolar dominance has been shown in some cases to involve methylation, patterns of variation were examined at methylation-susceptible sites. Third, patterns of substitution at conserved sites (including those which are likely to contribute to secondary structure in rRNA) in the 5.8S rDNA were examined. These analyses consistently indicated that one rDNA sequence type present in a broad range of Indo-Pacific Acropora species is likely to consist predominantly of pseudogenes. Patterns of variation also suggest that species may differ with respect to which rDNA sequence types have been silenced and which are active. These pseudogenes are likely to have arisen as a consequence of the introduction of highly divergent rDNA types into single genomes by interspecific hybridization events, and we attribute the extreme rDNA diversity characteristic of many Acropora species to both the independent evolution of these silenced rDNA types and to the suppressive effects of high sequence diversity on homogenizations processes acting on functional loci. Key Words:
ribosomal DNA, pseudogenes, ITS, reticulate evolution, coral, Acropora
© 2003 Society for Molecular Biology and Evolution
Original Articles
Pseudogenes Contribute to the Extreme Diversity of Nuclear Ribosomal DNA in the Hard Coral Acropora
2 Comparative Genomics Centre, James Cook University, Townsville, Queensland, 4810
3 Biochemistry and Molecular Biology, James Cook University, Townsville, Queensland, 4810; Marine Biology and Aquaculture, James Cook University, Townsville, Queensland, 4810
4 Australian Institute of Marine Science, PMB No. 3, Townsville MC, Queensland, 4810
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