The nucleolus organizer regions (Nor loci) of hexaploid wheat cultivars

1992 ◽  
Vol 43 (5) ◽  
pp. 889 ◽  
Author(s):  
CE May ◽  
R Appels
Keyword(s):  
Dna Sequences ◽  
Intergenic Spacer ◽  
Wheat Breeding ◽  
Nucleolus Organizer ◽  
Rrna Genes ◽  
F1 Hybrids ◽  
Dna Fragments ◽  
Wheat Cultivars ◽  
Nucleolus Organizer Regions ◽  
Spacer Dna

We have used the techniques of molecular genetics to analyse the nucleolus organizer regions (Nor loci) of a broad range of Australian, Chinese, and other hexaploid wheats (Triticum aestivum L. em Thell.). Genomic DNA was extracted from the leaves of 260 wheat cultivars, 94 different F1 hybrids, and from more than 800 F2 plants. Samples of the DNA were digested with the restriction enzyme TaqI and electrophoretically separated in agarose gels. The DNA fragments were then transferred to DNA filters by Southern blotting and assayed with the probe pTa250.4. This probe specifically detects the intergenic spacer DNA sequences which alternate with the ribosomal-RNA (rRNA) genes in highly repeated tandem arrays within the Nor loci. Analyses of the spacer DNA restriction fragments present in P, F1 and F2 plants show that allelic variants of the Nor loci can be distinguished by the existence of different lengths of spacer DNA fragments, different combinations of different length fragments, or differing amounts of the same length fragments. Eight alleles of the Nor-B1 locus on chromosome 1B (Nor-Bla to Nor-B1h) and 20 variants of the Nor-B2 locus on chromosome 6B (Nor-B2a to Nor-B2t) have been identified. The DNA fragments present in the different alleles are expressed in a co-dominant fashion to give phenotypic F2 ratios of 1 : 2 : 1 and 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1, indicating segregation at one or two loci, respectively. With two exceptions, individual alleles segregated in a 1 : 1 ratio. On the basis of the presence of different combinations of Nor-B1 and Nor-B2 alleles, the wheat cultivars investigated were divided into 53 phenotypic groups. These groups clearly reflect the germplasm used in wheat breeding programs in different countries. Hybrid wheats could also be recognized and plants with new combinations of alleles were produced.

scholarly journals Phylogenetic Analysis of Pines Based on Chloroplast trnT-trnL Intergenic Spacer DNA Sequences

2014 ◽  
Vol 30 (3) ◽  
pp. 307-313
Author(s):  
Yurry Um ◽  
Won-Kyu Park ◽  
Nam-Su Jo ◽  
Sim-Hee Han ◽  
Yi Lee
Keyword(s):  
Phylogenetic Analysis ◽  
Dna Sequences ◽  
Intergenic Spacer ◽  
Spacer Dna

The nucleolus

2019 ◽  
pp. 147-152
Author(s):  
John C. Lucchesi
Keyword(s):  
Gene Silencing ◽  
Histone H1 ◽  
Nucleolus Organizer ◽  
Linker Histone ◽  
The Other ◽  
Rrna Genes ◽  
Rrna Gene ◽  
Dna Repeats ◽  
Gene Arrays ◽  
Nucleolus Organizer Regions

The nucleolus forms at nucleolus organizer regions (NORs) that consist of clusters of repeated rRNA genes. Transcription of the rRNA genes and processing of the transcripts yields the three types of RNAs necessary for the biogenesis of ribosomes. Only subsets of the rRNA genes present in cells are transcribed. The linker histone H1 plays a specific role in the repression of inactive rRNA genes and in many of the other functions of the nucleolus. One of these functions is gene silencing—the nucleolus is surrounded by a zone of heterochromatin consisting of silenced rRNA gene arrays, DNA repeats that flank the centromeres and chromatin domains that include gene-poor, as well as silent, regions of the genome; any gene associating with this zone is subjected to repression. Other functions include the assembly of telomerase, the regulation of p53 stability and the synthesis of 5S and tRNAs whose genes form clusters in the nucleolus.

Impatiens bullatisepala (Balsaminaceae), a new species from Guizhou, China

Phytotaxa ◽  
2021 ◽  
Vol 500 (3) ◽  
pp. 217-224
Author(s):  
SHUAI PENG ◽  
YI-YAN CONG ◽  
JING TIAN ◽  
CAI-FEI ZHANG ◽  
GUANG-WAN HU ◽  
...  
Keyword(s):  
New Species ◽  
Dna Sequences ◽  
Phylogenetic Analyses ◽  
Intergenic Spacer ◽  
Guizhou Province ◽  
Abaxial Surface ◽  
Nuclear Its ◽  
A New Species ◽  
Spacer Dna

Impatiens bullatisepala (Balsaminaceae), a new species supported by morphological and phylogenetic evidence from Fanjing Mountain, Guizhou province in China, is described here. It is morphologically similar to I. davidii but can be distinguished by its dorsally ridged lateral sepals with sunk reticulate veins and bullate projections on abaxial surface, 2–2.5 cm deep saccate lower sepal with ca. 0.8 cm long narrowly triangular tip at the mouth, and broadly ovate dorsal petal. Phylogenetic analyses of a combined dataset of nuclear ITS and plastid atpB-rbcL intergenic spacer DNA sequences furtherly confirmed its novelty.

scholarly journals Selective nucleolus organizer inactivation in Arabidopsis is a chromosome position-effect phenomenon

2016 ◽  
Vol 113 (47) ◽  
pp. 13426-13431 ◽  
Author(s):  
Gireesha Mohannath ◽  
Frederic Pontvianne ◽  
Craig S. Pikaard
Keyword(s):  
Position Effect ◽  
Nucleolus Organizer ◽  
Rrna Genes ◽  
Rrna Gene ◽  
Chromosome 2 ◽  
Chromosome 4 ◽  
Base Pairs ◽  
Genomic Change ◽  
Nucleolus Organizer Regions ◽  
Chromosome Position

Nucleolus organizer regions (NORs) are chromosomal loci where hundreds of rRNA genes are clustered. Despite being nearly identical in sequence, specific rRNA genes are selected for silencing during development via choice mechanism(s) that remain unclear. In Arabidopsis thaliana, rRNA gene subtypes that are silenced during development were recently mapped to the NOR on chromosome 2, NOR2, whereas active rRNA genes map to NOR4, on chromosome 4. In a mutant line deficient for ATXR5 or ATXR6-dependent histone H3 lysine 27 (H3K27) monomethylation, we show that millions of base pairs of chromosome 4, including the telomere, TEL4N, and much of NOR4, have been converted to the corresponding sequences of chromosome 2. This genomic change places rRNA genes of NOR2, which are normally silenced, at the position on chromosome 4 where active rRNA genes are normally located. At their new location, NOR2-derived rRNA genes escape silencing, independent of the atxr mutations, indicating that selective rRNA gene silencing is chromosome 2-specific. The chromosome 2 position effect is not explained by the NOR2-associated telomere, TEL2N, which remains linked to the translocated NOR, implicating centromere-proximal sequences in silencing.

scholarly journals G banding in two species of grasshopper and its relationship to C, N, and fluorescence banding techniques

Genome ◽  
1991 ◽  
Vol 34 (4) ◽  
pp. 638-643 ◽  
Author(s):  
J. P. M. Camacho ◽  
J. Cabrero ◽  
E. Viseras ◽  
M. D. Lopez-Leon ◽  
J. Navas-Castillo ◽  
...  
Keyword(s):  
Mechanism Of Action ◽  
Dna Sequences ◽  
Locusta Migratoria ◽  
Nucleolus Organizer ◽  
Banding Technique ◽  
Eyprepocnemis Plorans ◽  
Grasshopper Species ◽  
Nucleolus Organizer Regions ◽  
Dapi Banding ◽  
Regular Patterns

A G banding technique combining trypsin and hot saline treatments was used to analyze the chromosomes of two grasshopper species, Eyprepocnemis plorans and Locusta migratoria, both of which contain both standard and supernumerary heterochromatin. Although this technique does not produce G bands like those in mammalian chromosomes, it serves to characterize heterochromatic regions whose nature has been inferred from other banding techniques (C, N, CMA, and DAPI banding). The light regions revealed by G banding contain GC-rich DNA sequences, the more prominent of which coincide with nucleolus organizer regions (NORs). Furthermore, the proximal heterochromatin in E. plorans was heterogeneous, and the standard and supernumerary heterochromatin showed conspicuous differences in organization. Supernumerary heterochromatin is an exception to the regular patterns shown by the standard heterochromatin. The findings are related to the mechanism of action of these banding techniques.Key words: banding techniques, grasshoppers, Eyprepocnemis plorans, Locusta migratoria.

Karyotyping Melandrium album, a dioecious plant with heteromorphic sex chromosomes

Genome ◽  
1990 ◽  
Vol 33 (4) ◽  
pp. 556-562 ◽  
Author(s):  
D. D. Ciupercescu ◽  
J. Veuskens ◽  
A. Mouras ◽  
D. Ye ◽  
M. Briquet ◽  
...  
Keyword(s):  
In Situ Hybridization ◽  
Sex Chromosomes ◽  
Nucleolus Organizer ◽  
Rrna Genes ◽  
Hybridization Technique ◽  
Metaphase Chromosomes ◽  
Nucleolus Organizer Regions ◽  
Melandrium Album ◽  
Group B

Mitotic metaphase chromosomes of Melandrium album obtained from root protoplasts were studied. Morphologically, the chromosomes were either metacentrics or submetacentrics. They were classified into three distinct groups: group A comprising six pairs of autosomal metacentrics, group B comprising five pairs of autosomal submetacentrics, and the sex chromosomes: X and Y. The X chromosome is a metacentric (r = 1.44), which accounts for more than 14% of the genome. The Y chromosome is a metacentric with, virtually, equal arms (r = 1.09) and accounts for 21% of the genome, being the largest of the complement. The Y:X ratio was 1.4. Ethidium bromide, caffeine, and vinblastine were used to obtain a better resolution and higher frequency of satellited chromosomes 7q and 9p. The proposed karyotype of M. album is 2n = 24, XX, s(7q;9p) for female and 2n = 24, XY, s(7q;9p) for male plants. Nucleolus organizer regions (NORs) were present at the telomeric sites of three chromosome pairs: 7q, 9p, and 10p. The NORs were polymorphic, particularly between the nonhomologous chromosomes. The in situ hybridization technique localized the rRNA genes on four chromosome pairs: 5p, 7q, 9p, and 10p. The discrepancy between the NORs and the hybridization signals was probably due to the fact that NORs were restricted only to transcriptionally active rRNA genes. It was concluded that for a complete description and characterization of rRNA genes, both NOR detection and in situ hybridization techniques, as complementary methods, should be employed.Key words: Melandrium album, karyotype, satellites, idiogram, nucleolus organizer regions, in situ hybridization.

scholarly journals Chromosome Banding in Amphibia. XXXIII. Demonstration of 5-Methylcytosine-Rich Heterochromatin in Anura

2016 ◽  
Vol 148 (1) ◽  
pp. 35-43
Author(s):  
Michael Schmid ◽  
Claus Steinlein
Keyword(s):  
Dna Sequences ◽  
Nucleolus Organizer ◽  
Major Influence ◽  
Banding Patterns ◽  
Nucleolus Organizer Regions ◽  
Experimental Parameters ◽  
Species Specific ◽  
Antibody Labeling ◽  
Chromosome Regions

An experimental approach using monoclonal anti-5-methylcytosine (5-MeC) antibodies and indirect immunofluorescence was elaborated for detecting 5-MeC-rich chromosome regions in anuran chromosomes. This technique was applied to mitotic metaphases of 6 neotropical frog species belonging to 6 genera and 4 families. The hypermethylation patterns were compared with a variety of banding patterns obtained by conventional banding techniques. The hypermethylated DNA sequences are species-specific and located exclusively in constitutive heterochromatin. They are found in centromeric, pericentromeric, telomeric, and interstitial positions of the chromosomes and adjacent to nucleolus organizer regions. 5-MeC-rich DNA sequences can be embedded both in AT- and GC-rich repetitive DNA. The experimental parameters that have major influence on the reproducibility and quality of the anti-5-MeC antibody labeling are discussed.

scholarly journals Chromosomal stasis in distinct families of marine Percomorpharia from South Atlantic

2017 ◽  
Vol 11 (2) ◽  
pp. 299-307 ◽  
Author(s):  
Fabilene Gomes Paim ◽  
Leandro Aragão da Hora Almeida ◽  
Paulo Roberto Antunes de Mello Affonso ◽  
Patrícia Elda Sobrinho-Scudeler ◽  
Claudio Oliveira ◽  
...  
Keyword(s):  
Nucleolus Organizer ◽  
Rrna Genes ◽  
Centromeric Heterochromatin ◽  
Single Pair ◽  
Nucleolus Organizer Regions ◽  
Chromosomal Data ◽  
Physical Barriers ◽  
5S Rrna Genes ◽  
Fish Group ◽  
Acrocentric Chromosomes

The weakness of physical barriers in the marine environment and the dispersal potential of fish populations have been invoked as explanations of the apparent karyotype stasis of marine Percomorpha, but several taxa remain poorly studied cytogenetically. To increase the chromosomal data in this fish group, we analyzed cytogenetically three widespread Atlantic species from distinct families: Chaetodipterusfaber Broussonet, 1782 (Ephippidae), Lutjanussynagris Linnaeus, 1758 (Lutjanidae) and Rypticusrandalli Courtenay, 1967 (Serranidae). The three species shared a karyotype composed of 2n=48 acrocentric chromosomes, single nucleolus organizer regions (NORs) and reduced amounts of centromeric heterochromatin. A single NOR-bearing pair was identified in all species by physical mapping of 18S rDNA while non-syntenic 5S rRNA genes were located at centromeric region of a single pair. The similar karyotypic macrostructure observed in unrelated groups of Percomorpharia reinforces the conservative karyoevolution of marine teleosteans. Nonetheless, the species could be differentiated based on the pair bearing ribosomal cistrons, revealing the importance of microstructural analyses in species with symmetric and stable karyotypes.

scholarly journals Targeted Enrichment of rRNA Gene Tandem Arrays for Ultra-Long Sequencing by Selective Restriction Endonuclease Digestion

2021 ◽  
Vol 12 ◽  
Author(s):  
Anastasia McKinlay ◽  
Dalen Fultz ◽  
Feng Wang ◽  
Craig S. Pikaard
Keyword(s):  
Ribosomal Rna ◽  
Reference Genome ◽  
Nucleolus Organizer ◽  
Rrna Genes ◽  
Rrna Gene ◽  
Simple Method ◽  
Nucleolus Organizer Regions ◽  
Oxford Nanopore ◽  
Endonuclease Digestion ◽  
Targeted Enrichment

Large regions of nearly identical repeats, such as the 45S ribosomal RNA (rRNA) genes of Nucleolus Organizer Regions (NORs), can account for major gaps in sequenced genomes. To assemble these regions, ultra-long sequencing reads that span multiple repeats have the potential to reveal sets of repeats that collectively have sufficient sequence variation to unambiguously define that interval and recognize overlapping reads. Because individual repetitive loci typically represent a small proportion of the genome, methods to enrich for the regions of interest are desirable. Here we describe a simple method that achieves greater than tenfold enrichment of Arabidopsis thaliana 45S rRNA gene sequences among ultra-long Oxford Nanopore Technology sequencing reads. This method employs agarose-embedded genomic DNA that is subjected to restriction endonucleases digestion using a cocktail of enzymes predicted to be non-cutters of rRNA genes. Most of the genome is digested into small fragments that diffuse out of the agar plugs, whereas rRNA gene arrays are retained. In principle, the approach can also be adapted for sequencing other repetitive loci for which gaps exist in a reference genome.

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