Ribosomal RNA genes in Scots pine (Pinus sylvestris L.): Chromosomal organization and structure |
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Authors: | Päivi Karvonen Matti Karjalainen Outi Savolainen |
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Institution: | (1) Department of Genetics, University of Oulu, 90570 Oulu, Finland |
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Abstract: | The nuclear 18S, 5.8S and 25S rRNA genes exist as thousands of rDNA repeats in the Scots pine genome. The number and location
of rDNA loci (nucleolus organizers, NORs) were studied by cytological methods, and a restriction map from the coding region
of the Scots pine rDNA repeat was constructed using digoxigenin-labeled flax rDNA as a probe. Based on the maximum number
of nucleoli and chromosomal secondary constrictions, Scots pine has at least eight NORs in its haploid genome. The size of
the Scots pine rDNA repeat unit is approximately 27 kb, two- or threefold larger than the typical angiosperm rDNA unit, but
similar in size to other characterized conifer rDNA repeats. The intergenic spacer region (IGS) of the rDNA repeat unit in
Scots pine is longer than 20 kb, and the transcribed spacer regions surrounding the 5.8S gene (ITS1 and ITS2) span a region
of 2.9 kb. Restriction analysis revealed that although the coding regions of rDNA repeats are homogeneous, heterogeneity exists
in the intergenic spacer region between individuals, as well as among the rDNA repeats within individuals. |
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Keywords: | digoxigenin-labeling nucleolus organizers Pinus restriction map rDNA |
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