The Molecular Basis of Variation Affecting Gene Expression: Evidence from Studies on the Ribosmal RNA Gene Loci of Wheat

Flavell, R. B.; Sardana, Ravinder; Jackson, Stephen D.; O’Dell, M.

doi:10.1007/978-1-4684-7047-5_22

Cited by 7 publications

(9 citation statements)

References 19 publications

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“…We investigated whether the number and location of the rDNA loci is the sum of that found in the putative parents, and whether concerted evolution has altered or homogenised units as has occurred in N. tabacum. The results are also interpreted in the light of other rDNA unit arrays previously described in allopolyploids in Triticum (Flavell, 1990), Brassica (Chen and Pikaard, 1997) and Gossypium (Wendel et al, 1995a).…”

Section: Introductionmentioning

confidence: 53%

“…In wheat (Triticum aestivum), a 10 000-year-old allohexapolyploid, subrepeats are found in the IGS (Barker et al, 1988) as in tobacco (Volkov et al, 1999). In wheat, the structure of the A-type subrepeat varies little, but their copy number differs among loci and cultivars (Flavell, 1990). In wild populations of tetraploid wheats, the IGS in some populations is heterogeneous whereas in others it is homogeneous (Flavell et al, 1986), indicating both divergence, homogenisation and fixation of subrepeat number (Flavell, 1989), processes that are probably similar to what has occurred in N. rustica.…”

Section: Discussionmentioning

confidence: 99%

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Ribosomal DNA evolution and gene conversion in Nicotiana rustica

et al. 2003

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Genomic in situ hybridisation was used to confirm that Nicotiana rustica (2n ¼ 4x ¼ 48) is an allotetraploid between N. paniculata (2n ¼ 2x ¼ 24, maternal P-genome donor) and N. undulata (2n ¼ 2x ¼ 24, paternal U-genome donor), their progenitors or species closely related to them. Fluorescent in situ hybridisation showed that N. paniculata has one 5S and two 18-5.8-26S rDNA loci whereas N. undulata has an additional 18-5.8-26S rDNA locus. N. rustica has the sum of the loci found in these putative parents. The sizes of the 18-5.8-26S rDNA loci indicate that the number of rDNA units on the U-genome chromosomes has amplified; perhaps this is associated with a concomitant reduction in the number of units on P-genome chromosomes. Restriction fragment length polymorphism analysis of the intergenic spacer (IGS) of the 18-5.8-26S rDNA units in N. rustica and the two progenitor diploids revealed that about 80% of IGS sequences in N. rustica are of an N. undulata type and 20% of N. paniculata type. These data indicate that interlocus sequence homogenisation has caused the replacement of many N. paniculata-type IGSs in N. rustica with an N. undulata-type of sequence. It is probable that subsequent to this replacement there has been sequence divergence at the 5 0 end of the IGS. As in tobacco, an allotetraploid between N. sylvestris and N. tomentosiformis, the direction of the IGS interlocus conversion is towards the paternal genome donor.

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Section: Introductionmentioning

confidence: 53%

Section: Discussionmentioning

confidence: 99%

Ribosomal DNA evolution and gene conversion in Nicotiana rustica

et al. 2003

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“…Perhaps many other genes are also unequally expressed due to the dierential anity of their promoters and enhancers for regulatory molecules. If so, mechanisms similar to those revealed for ribosomal RNA genes in new heterozygous backgrounds might be the basis of the dierential gene expression recognized by breeders and geneticists (Flavell et al 1990). …”

Section: Discussionmentioning

confidence: 99%

“…NOR expression, it was concluded that NOR expression is aected by (a) the number of genes at a locus (Flavell 1989;Sardana et al 1993), (b) the number of enhancers/regulatory sequences associated with the genes, and (c) the anities of the enhancers and promoters for regulatory proteins (Flavell 1986(Flavell , 1989Jackson and Flavell 1992). A model was proposed to account for how genes were selected for transcription (Flavell 1986(Flavell , 1989Flavell et al 1990). The model involved competition between accessible promoter and enhancer sequences for regulatory proteins in limiting concentration.…”

Section: Introductionmentioning

confidence: 99%

Cytosine methylation and nucleolar dominance in cereal hybrids

et al. 1997

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In wheat-rye hybrids the nucleolus organizer regions (NORs), the sites of ribosomal RNA genes, from rye are suppressed. Wheat and wheat-rye hybrid genetic stocks containing different numbers of wheat and rye nucleolus organizers, as well as addition lines and rye-barley hybrids, were used in Southern hybridization experiments to determine the cause of nucleolar dominance and suppression in cereal hybrids. Based on the use of restriction endonucleases that cleave near the ends of the spacer unit and an additional, methylation-sensitive enzyme, HpaII, which does not recognize the CCGG restriction site if the internal C is methylated, an indirect method of assaying NOR expression was established. The results indicated that cleavage by the HpaII enzyme of the rye NOR sequences, is reduced when major NORs from other cereals were present. The reduction in the number of rye rRNA genes containing an unmethylated CCGG site in the promoter was associated with the suppression of the rye nucleolus. These results are consistent with a model in which promoter and upstream regulatory repeats of ribosomal RNA genes compete for limited concentrations of regulatory proteins, and genes that are methylated at key binding sites fail to engage these regulatory proteins and thus remain inactive.

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“…The DNA sequences and the lengths of the intergenic regions frequently differ between rRNA genes of the same species, and also of closely related species [1,8]. These differences correlate with the observed differential activity of rDNA loci in the same nucleus [ 10]. This phenomenon of differential expression is known as nucleolar dominance.…”

Section: Introductionmentioning

confidence: 83%

Protein-binding to reiterated motifs within the wheat rRNA gene promoter and upstream repeats

Jackson

Flavell

1992

Plant Mol Biol

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The binding of specific proteins in wheat nuclear extracts to the -34 to +10 region of the wheat ribosomal RNA gene promoter has been detected. DNase I footprinting revealed two binding regions, one spanning the transcription initiation site from -7 to +2, and a larger one further upstream from around -29 to -15. An oligonucleotide made to the -30 to -14 promoter region binds a protein in a sequence-specific manner. This protein also binds specifically to sites with related sequences further upstream in the promoter and in the associated intergenic spacer repeats. A consensus sequence, CATGG--GC-AAAAC, was defined from the different binding sites of the protein. These results, taken together with in vivo results on the enhanced activity of nucleoli containing ribosomal RNA genes with more intergenic spacer repeats, endorse the hypothesis that ribosomal RNA gene transcription is regulated by the extent of binding of a protein to many sites upstream of the transcriptional start site.

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The Molecular Basis of Variation Affecting Gene Expression: Evidence from Studies on the Ribosmal RNA Gene Loci of Wheat

Cited by 7 publications

References 19 publications

Ribosomal DNA evolution and gene conversion in Nicotiana rustica

Ribosomal DNA evolution and gene conversion in Nicotiana rustica

Cytosine methylation and nucleolar dominance in cereal hybrids

Protein-binding to reiterated motifs within the wheat rRNA gene promoter and upstream repeats

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