title: Transcription activity of rRNA genes correlates with a tendency towards intergenomic homogenization in Nicotiana allotetraploids.
abstract: This paper establishes relationships between two aspects of ribosomal DNA (rDNA) biology: epigenetic silencing of rDNA loci; and homogenization leading to concerted evolution. Here, we examined rDNA inheritance and expression patterns in three natural Nicotiana allopolyploids (closest living descendants of diploid parents are given), N. rustica (N. paniculata x N. undulata), N. tabacum (N. sylvestris x N. tomentosiformis) and N. arentsii (N. undulata x N. wigandioides), and synthetic F(1) hybrids and allopolyploids. The extent of interlocus rDNA homogenization decreased in the direction N. arentsii > N. tabacum > N. rustica. The persistence of parental rDNA units in one of the subgenomes was associated with their transcription inactivity and likely heterochromatization. Of synthetic hybrids and polyploids only N. paniculata x N. undulata showed strong uniparental transcriptional silencing of rDNA triggered already in F(1). Epigenetic patterns of expression established early in allopolyploid nucleus formation may render units susceptible or resistant to homogenization over longer time-frames. We propose that nucleolus-associated transcription leaves rDNA units vulnerable to homogenization, while epigenetically inactivated units, well-separated from the nucleolus, remain unconverted.
authors: Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno CZ-61265, Czech Republic.
authors: Martina
authors: M
authors: Dadejová
authors: School of Biological and Chemical Sciences, Queen Mary, University of London, London, E1 4NS, UK.
authors: K Yoong
authors: KY
authors: Lim
authors: Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno CZ-61265, Czech Republic.
authors: Kamila
authors: K
authors: Soucková-Skalická
authors: Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno CZ-61265, Czech Republic.
authors: Roman
authors: R
authors: Matyášek
authors: Laboratoire de Biologie Cellulaire, Institut Jean-Pierre Bourgin, INRA - Centre de Versailles, F-78026, Versailles cedex, France.
authors: Marie-Angéle
authors: MA
authors: Grandbastien
authors: School of Biological and Chemical Sciences, Queen Mary, University of London, London, E1 4NS, UK.
authors: Andrew
authors: A
authors: Leitch
authors: Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno CZ-61265, Czech Republic.
authors: Aleš
authors: A
authors: Kovařík
mesh_terms: D004275:DNA, Ribosomal / Q000235:genetics; D020868:Gene Silencing; D020459:Genes, rRNA; D018745:Genome, Plant; D011123:Polyploidy; D018749:RNA, Plant / Q000235:genetics*; D014026:Nicotiana / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D004275:DNA, Ribosomal; D018749:RNA, Plant