Molecular-cytogenetic studies of ribosomal genes and heterochromatin reveal conserved genome organization among 11 Quercus species |
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Authors: | V Zoldos D Papes M Cerbah O Panaud V Besendorfer S Siljak-Yakovlev |
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Institution: | (1) Department of Molecular Biology, Faculty of Science, University of Zagreb, Rooseveltov trg 6, 10 000 Zagreb, Croatia, XX;(2) Laboratoire d’Evolution et Systématique, UPRESA – CNRS 8079, Université Paris XI, Batiment 360, 91405 Orsay Cedex, France e-mail: vlatka.Zoldos@esv.u-psud.fr, FR |
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Abstract: | Genomes of 11 Quercus species were characterized using cytogenetic (Giemsa C-banding, fluorochrome banding), molecular-cytogenetic (fluorescence in situ hybridization, FISH, to ribosomal genes) and molecular (dot-blot for ribosomal gene-copy number assessment) techniques. Ribosomal
genes are the first DNA sequences to be physically mapped in oaks, and the copy number of the 18S-5.8S-26 S rRNA genes is
estimated for the first time. Oak karyotypes were analysed on the basis of DAPI banding and FISH patterns; five marker chromosomes
were found. In addition, chromosomal organization of ribosomal genes with respect to AT- and GC-differentiated heterochromatin
was studied. Fluorochrome staining produced very similar CMA/DAPI banding patterns, and the position and number of ribosomal
loci were identical for all the species studied. The 18S-5.8S-26 S rRNA genes in oak complements were represented by a major
locus at the subterminal secondary constriction (SC) of the only subtelocentric chromosome pair and a minor locus at paracentromeric
SC of one metacentric pair. The only 5 S rDNA locus was revealed at the paracentromeric region of the second largest metacentric
pair. A striking karyotypic similarity, shown by both fluorochrome banding and FISH patterns, implies close genome relationships
among oak species no matter their geographic origin (European or American) or their ecophysiology (deciduous or evergreens).
Dot-blot analysis gave preliminary evidence for different copy numbers of 18S-5.8S-26 S rRNA genes in diploid genomes of Q. cerris, Q. ilex, Q. petraea, Q. pubescens and Q. robur (2700, 1300, 2200, 4000 and 2200 copies, respectively) that was correlated with the size polymorphism of the major locus.
Received: 26 February 1999 / Accepted: 16 March 1999 |
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Keywords: | Quercus Fluorochrome banding FISH Heterochromatin Karyotype 18S-5 8S-26 S and 5 S rRNA genes |
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