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  • 1
    ISSN: 1432-2242
    Keywords: Key words Satellite DNA ; Repetitive DNA ; Fluorescent in situ hybridization ; Beta vulgaris ; Dispersed repeats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In a search for repetitive DNA sequences in the sugar beet genome, two sequences with repeat unit lengths of 143 and 434 bp were isolated and characterized. The pSV family showed an unusual conservation of restriction sites reflecting homogenization of the analyzed repeats. Members of the family are organized as tandem repeats as revealed by PCR and sequencing of dimeric units. The pSV satellite occurs in large intercalary arrays which are present on all chromosome arms of sugar beet. The pSV sequence family is present in different abundance in the sections Beta, Corollinae and Nanae but is not detectable by Southern hybridization in the section Procumbentes. The pDRV family is characterized by an interspersed genomic organization. The sequence is detectable in all sections of the genus and is amplified in species of the section Beta but was also detected, although at lower abundance, in the remaining three sections. Fluorescent in situ hybridization has shown that the pDRV sequence family is dispersed over all chromosomes of the sugar beet complement with some regions of clustering and centromeric depletion.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: Beta vulgaris ; Sugar beet ; In-situ hybridization ; rRNA genes ; Intergenic spacer ; Physical mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A digoxigenin-labelled 5S rDNA probe (pTa-794) and a rhodamine-labelled 18S-5.8S-25S rDNA probe (pTa71) were used for double-target in-situ hybridization to root-tip metaphase, prophase and interphase chromosomes of cultivated beet,Beta vulgaris L. After in-situ hybridization with the 18S-5.8S-25S rDNA probe, one major pair of sites was detected which corresponded to the secondary constriction at the end of the short arm of chromosome 1. The two rDNA chromosomes were often associated and the loci only contracted in late metaphase. In the majority of the metaphase plates analyzed, we found a single additional minor hybridization site with pTa71. One pair of 5S rRNA gene clusters was localized near the centromere on the short arm of one of the three largest chromosomes which does not carry the 18S-5.8S-25S genes. Because of the difficulties in distinguishing the very similarly-sizedB. vulgaris chromosomes in metaphase preparations, the 5S and the 18S-5.8S-25S rRNA genes can be used as markers for chromosome identification. TwoXbaI fragments (pXV1 and pXV2), comprising the 5S ribosomal RNA gene and the adjacent intergenic spacer, were isolated. The two 5S rDNA repeats were 349 bp and 351 bp long, showing considerable sequence variation in the intergenic spacer. The use of fluorescent in-situ hybridization, complemented by molecular data, for gene mapping and for integrating genetic and physical maps of beet species is discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-6849
    Keywords: Beta vulgaris ; in situ hybridization ; LINE ; LTR retrotransposons ; non-LTR (non-viral) retrotransposons ; Ty1-copia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract DNA sequences of the reverse transcriptase gene of long terminal repeat (LTR) and non-LTR (non-viral) retrotransposons have been isolated and cloned from the genome of sugar beet (Beta vulgaris). Both retrotransposon types are highly amplified in sugar beet and may account for 2–5% of the genome. The BNR1 family, representing the first non-viral retrotransposon reported from a dicotyledonous species, shows homology to the mammalian L1 family of long interspersed repeated sequences (LINEs) and to retrotransposable elements from maize and lily. Sequences of the Tbv family are homologous to theTy1-copia class of LTR retrotransposons. The BNR1 and Tbv retrotransposon families are characterized by sequence heterogeneity and are probably defective. The deduced peptide sequences were used to investigate the relation to other retroelements from plants, insects and mammals. Fluorescencein situ hybridization was used to investigate the physical distribution and revealed that both retrotransposon families are present on all sugar beet chromosomes and largely excluded from chromosomal regions harbouring the 18S–5.8S–25S rRNA genes. The BNR1 family is organized in discrete clusters, while the Tbv family ofTy1-copia-like retrotransposons shows a more uniform distribution along chromosome arms and is absent from some chromosomal regions. These contrasting distributions emphasize the differences in evolutionary amplification and dispersion mechanisms between the two types of retrotransposons. Thein situ results of both elements reflect significant features of a higher order structure of the genome, as it is known for both short interspersed repeated sequences (SINEs) and LINEs in human.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-5028
    Keywords: Beta procumbens ; Beta vulgaris ; in situ hybridization ; repetitive DNA ; satellite DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Members of three prominent DNA families of Beta procumbens have been isolated as Sau3A repeats. Two families consisting of repeats of about 158 bp and 312 bp are organized as satellite DNAs (Sau3A satellites I and II), whereas the third family with a repeat length of 202 bp is interspersed throughout the genome. Multi-colour fluorescence in situ hybridization was used for physical mapping of the DNA families, and has shown that these tandemly organized families occur in large heterochromatic and DAPI positive blocks. The Sau3A satellite I hybridized exclusively around or near the centromeres of 10, 11 or 12 chromosomes. The Sau3A satellite family I showed high intraspecific variability and high-resolution physical mapping was performed on pachytene chromosomes using differentially labelled repeats. The physical order of satellite subfamily arrays along a chromosome was visualized and provided evidence that large arrays of plant satellite repeats are not contiguous and consist of distinct subfamily domains. Re-hybridization of a heterologous rRNA probe to mitotic metaphase chromosomes revealed that the 18S-5.8S-25S rRNA genes are located at subterminal position on one chromosome pair missing repeat clusters of the Sau3A satellite family I. It is known that arrays of Sau3A satellite I repeats are tightly linked to a nematode (Heterodera schachtii) resistance gene and our results show that the gene might be located close to the centromere. Large arrays of the Sau3A satellite II were found in centromeric regions of 16 chromosomes and, in addition, a considerable interspersion of repeats over all chromosomes was observed. The family of interspersed 202 bp repeats is uniformly distributed over all chromosomes and largely excluded from the rRNA gene cluster but shows local amplification in some regions. Southern hybridization has shown that all three families are specific for genomes of the section Procumbentes of the genus Beta.
    Type of Medium: Electronic Resource
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