The Relationship between Satellite Deoxyribonucleic Acid, Ribosomal Ribonucleic Acid Gene Redundancy, and Genome Size in Plants

Abstract

The buoyant density of ribosomal DNA is similar in species with or without satellite DNA, and in all species examined was distinguishable from that of the satellite DNA. In melon tis- Because there is little cytological evidence for extrachromosomal DNA replication during plant development and no evidence for massive rDNA amplification (1), the observed correlation between satellite DNA and rDNA in plants requires further examination. The similarity in buoyant density between satellite and rDNA may be fortuitous, for rDNA has a similar density in species containing no satellite DNA (9, 16). Furthermore, a high percentage hybridization with rRNA does not necessarily imply a high redundancy of the rRNA gene, inasmuch as determination of this latter value depends on the size of the genome. In fact, high numbers of rRNA genes are found in species with low percentage hybridization but with large genomes (10, 18). The relationship between satellite DNA, defined as a minor component on neutral CsCl centrifugation, and rDNA has therefore been examined in terms of their respective buoyant densities in a larger range of plant species, and considered in the light of both percentage hybridization and the level of rRNA gene redundancy. MATERIALS AND METHODSDNA was prepared from total tissue by homogenization in a detergent mix followed by chloroform deproteinization. Further purification involved digestion with RNase and pronase, recovery by high speed centrifugation, and purification on a CsCl equilibrium density gradient (16). All DNA samples were monitored by Model E CsCl analytical centrifugation (19).Explants of artichoke (Helianthus tuberosus) were cultured in medium containing 3P orthophosphate or 3H uridine, and seedings of swisschard (Beta vulgaris var. cicla), pea (Pisum sativum), onion (Alliumn cepa), wheat (Triticum aestivum), flax (Linuin usitatissimnumn), maize (Zea inays) and Norway spruce (Picea abies) were grown in water culture in the presence of 32p orthophosphate for 5 to 10 days. Total nucleic acid was prepared and then fractionated by gel electrophoresis, and the cytoplasmic rRNAs, 1.3 x 106 and 0.7 X 106 daltons, were eluted and recovered by high speed centrifugation (16

Silenced rRNA genes are activated and substitute for partially eliminated active homeologs in the recently formed allotetraploid, Tragopogon mirus (Asteraceae)

“…It is estimated that about 100-200 genes are sufficient to cover metabolic demands in animals (Grummt and Pikaard, 2003). The situation is less clear in plants, which usually possess a high number of rRNA genes (typically thousands of copies Ingle et al, 1975) and in which considerable sequence and locus number variation exists among species of the same genus.…”

Strategies to maintain the stability of the ribosomal RNA gene repeats -Collaboration of recombination, cohesion, and condensation-

“…As Pol I transcription is required for rDNA amplification, the transcription seems to bias the recombination towards increasing the copy number by selection of the replicated region (around rARS-1 in Fig. 2-c), as a recombination target, although E. coli 7 (Ellwood and Nomura, 1982) Saccharomyces cerevisiae 150 (Kobayashi et al, 1998) Drosophila melanogaster 240 (Tartof, 1979) Xenopus laevis 600 (Wallance and Birnstiel, 1966) Homo sapiens 350 (Sakai et al, 1995) Arabidopsis thaliana 570 (Pruitt and Meyerowitz, 1986) Pisum sativum (pea) 3,900 (Ingle et al, 1975) For review see Long and Dawid (1980) the mechanism is not elucidated yet. Analysis of cis-acting factors .…”

Chloroplast DNA Sequence Homologies among Vascular Plants

“…All angiosperm reactions were at 150 jg/ml; others were at 600 jig/ml. a Diploid amounts in pg are given for pea, broad bean, corn and barley (6), daffodil (23), muskmelon (11); the values given for watermelon and squash show the range found for 5 other species in the same family (11). The genome sizes of Trillium erectum, (6), and T. grandiflorum, (11) (2).…”

“…a Diploid amounts in pg are given for pea, broad bean, corn and barley (6), daffodil (23), muskmelon (11); the values given for watermelon and squash show the range found for 5 other species in the same family (11). The genome sizes of Trillium erectum, (6), and T. grandiflorum, (11) (2). The experiments, using pea chloroplast DNA as a probe in reassociation reactions, show that the phylogenetically most distant species exhibit the greatest sequence divergence from pea.…”