Concerted evolution of rDNA in recently formed Tragopogon allotetraploids is typically associated with an inverse correlation between gene copy number and expression.
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).
Matyásek
Roman
R
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.
Tate
Jennifer A
JA
Lim
Yoong K
YK
Srubarová
Hana
H
Koh
Jin
J
Leitch
Andrew R
AR
Soltis
Douglas E
DE
Soltis
Pamela S
PS
Kovarík
Ales
A
D001483:Base Sequence; D002843:Chromatin / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D004171:Diploidy; D019143:Evolution, Molecular; D018628:Gene Dosage; D015870:Gene Expression; D017343:Genes, Plant; D005828:Genetics, Population; D007061:Idaho; D008969:Molecular Sequence Data; D009697:Nucleolus Organizer Region / Q000235:genetics; D018807:Polymorphism, Single-Stranded Conformational; D011123:Polyploidy; D031188:Tragopogon / Q000235:genetics*; D014861:Washington
D002843:Chromatin; D017931:DNA Primers; D018744:DNA, Plant; D004275:DNA, Ribosomal