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Originally published as Genetics Published Articles Ahead of Print on July 1, 2007.

Genetics, Vol. 176, 2509-2519, August 2007, Copyright © 2007
doi:10.1534/genetics.107.072751

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Concerted Evolution of rDNA in Recently Formed Tragopogon Allotetraploids Is Typically Associated With an Inverse Correlation Between Gene Copy Number and Expression

Roman Matyásek*, Jennifer A. Tate{dagger}, Yoong K. Lim{ddagger}, Hana Srubarová*, Jin Koh{dagger}, Andrew R. Leitch{ddagger}, Douglas E. Soltis{dagger}, Pamela S. Soltis§ and Ales Kovarík*,1

* Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i, Laboratory of Molecular Epigenetics, Královopolská 135, CZ-61265 Brno, Czech Republic, {dagger} Department of Botany, University of Florida, Gainesville, Florida 32611, {ddagger} School of Biological Sciences, Queen Mary, University of London, E1 4NS, UK and § Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611

1 Corresponding author: Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Laboratory of Molecular Epigenetics, Královopolská 135, CZ-612 65 Brno, Czech Republic.
E-mail: kovarik{at}ibp.cz

We analyzed nuclear ribosomal DNA (rDNA) transcription and chromatin condensation in individuals from several populations of Tragopogon mirus and T. miscellus, allotetraploids that have formed repeatedly within only the last 80 years from T. dubius and T. porrifolius and T. dubius and T. pratensis, respectively. We identified populations with no (2), partial (2), and complete (4) nucleolar dominance. It is probable that epigenetic regulation following allopolyploidization varies between populations, with a tendency toward nucleolar dominance by one parental homeologue. Dominant rDNA loci are largely decondensed at interphase while silent loci formed condensed heterochromatic regions excluded from nucleoli. Those populations where nucleolar dominance is fixed are epigenetically more stable than those with partial or incomplete dominance. Previous studies indicated that concerted evolution has partially homogenized thousands of parental rDNA units typically reducing the copy numbers of those derived from the T. dubius diploid parent. Paradoxically, despite their low copy number, repeats of T. dubius origin dominate rDNA transcription in most populations studied, i.e., rDNA units that are genetic losers (copy numbers) are epigenetic winners (high expression).






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Copyright © 2007 by the Genetics Society of America.