Ribosomal DNA spacer-length polymorphisms in barley: mendelian inheritance, chromosomal location, and population dynamics (original) (raw)
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Genetic and molecular organization of ribosomal DNA (rDNA) variants in wild and cultivated barley
Genetics, 1990
Twenty rDNA spacer-length variants (slvs) have been identified in barley. These slvs form a ladder in which each variant (with one exception) differs from its immediate neighbors by a 115-bp subrepeat. The 20 slvs are organized in two families, one forming an eight-step ladder (slvs 100-107) in the nucleolus organizer region (NOR) of chromosome 7 and the other a 12-step ladder (slvs 108a-118) in the NOR of chromosome 6. The eight shorter slvs (100-107) segregate and serve as markers of eight alleles of Mendelian locus Rrn2 and the 12 longer slvs (108a-118) segregate and serve as markers of 12 alleles of Mendelian locus Rrn1. Most barley plants (90%) are homozygous for two alleles, including one from each the 100-107 and the 108a-118 series. Two types of departures from this typical pattern of molecular and genetic organization were identified, one featuring compound alleles marked by two slvs of Rrn1 or of Rrn2, and the other featuring presence in Rrn1 of alleles normally found in R...
Proceedings of the National Academy of Sciences, 1990
DNA from 267 accessions of wild barley from ecologically diverse habitats in Israel and Iran and from 92 accessions of cultivated barley from throughout the world were assayed for the 20 ribosomal DNA (rDNA) spacer-length variants that have been identified in the barley species. These 20 spacer-length variants, which are detectable by Southern blot hybridization, serve as markers of rDNA alleles of two Mendelian loci, Rrnl and Rrn2. All of the populations of wild barley studied were polymorphic for both loci. In wild barley allele 112 (Rrnl) and allele 107 (Rrn2) behaved as widely adapted wild-type alleles; in our sample of cultivated barley allele 112 also behaved as a wild-type allele but allele 104 was somewhat more frequent than allele 107 in Rrn2. A few other alleles were locally frequent in wild barley. However, most of the 20 alleles were infrequent or rare and such alleles were often associated as "hitchhikers" with one of the wild-type alleles in compound two-component alleles. Allelic and genotypic frequencies differed widely in different habitats in correlation with eight of nine factors of the physical environment. Discrete log-linear multivariate analyses revealed statistically significant associations among alleles of Rrnl and Rrn2. It was concluded that natural selection acting differentially on various rDNA alleles plays a major role in the development and maintenance of observed patterns of molecular and genetic organization of rDNA variability.
Adaptive ribosomal DNA polymorphism in wild barley at a mosaic microsite, Newe Ya’ar in Israel
Plant Science, 2004
In eukaryotic genomes, ribosomal DNA is organized in tandem repeat units at the nucleolar organizing regions (NORs) on each satellited chromosome. Each repeat unit consists of a coding region and an intergenic spacer (IGS), the latter generally varying in length at different loci of the same genotype and also at the same locus in different genotypes. The spacer length variants (slvs) are sometimes correlated with climatic and ecological variables. In a study of 42 accessions of wild barley (Hordeum spontaneum) collected from four different microniches (sun-deep soil, sun-shallow soil, shade-deep soil and shade-shallow soil) at the Newe Ya'ar microsite (3182 m 2 ), in Israel, we observed eight slvs constituting 10 different rDNA phenotypes, correlated with edaphic conditions prevalent at the four microniches. We conclude that rDNA diversity in wild barley is distributed nonrandomly and adaptively in the four microniches of Newe Ya'ar. A novel feature in this study is also the homogenization of IGS length at the two loci located at two nonhomologous chromosomes. Fluorescence in situ hybridization (FISH), was used to rule out the possibility of loss of one of the two NOR loci.
Plant Science, 2004
Ribosomal DNA (rDNA) repeat unit length polymorphism was examined in 285 accessions of wild barley, Hordeum spontaneum C. Koch, which were collected from 27 locations across Jordan. As many as 19 spacer length variants (slvs) or rDNA alleles were available, which formed 70 slv phenotypes. The two missing alleles (098, 099) of the series (097, 100-118) and one additional allele 119 were also discovered in the present study thus raising the number of ribosomal slvs in barley to 24. Relatively more frequent rDNA alleles were analyzed in detail, and it was shown that they occurred non-randomly at locations with different environmental factors (annual rainfall, highest and lowest temperatures, altitude, longitude, latitude) and exhibited association with specific environments. Ecogeographical factors, rather than geographical factors per se, seem to affect the distribution of rDNA alleles. The present study thus demonstrates that rDNA repeat unit length polymorphism in some cases can be adaptive in nature.
Polymorphism at rDNA loci in barley and its relation with climatic variables
Theoretical and Applied Genetics, 2002
The variation in length of the intergenic spacer (IGS) region of the ribosomal DNA repeat unit was examined in 63 accessions of wild barley, Hordeum spontaneum, and seven accessions of cultivated barley, Hordeum vulgare. The accessions of wild barley were collected from ecologically diverse climatic and edaphic microsites in Israel, and the barley cultivars were those grown in India. Sixteen spacer-length variants (slvs) observed in the present study presumably belonged to two known rDNA loci (Rrn1 and Rrn2). Each accession had one or more variants, which together represented the rDNA phenotype. The rDNA phenotypes of wild barley accessions were widely diverse and differed substantially from those of cultivated barley. The slv phenotypes and the corresponding alleles were shown to be largely correlated with different climatic, edaphic and ecogeographical microsites and niches (the ”Evolution Canyon” at Lower Nahal Oren, Mount Carmel; and Tabigha, Eastern Upper Galilee Mountains), so that a particular rDNA phenotype of an accession could be used to predict the climate and soil to which the accession belonged. This sharp microsite ecogeographic variation in ribosomal DNA appears adaptive in nature, and is presumably driven by climatic and edaphic natural selection.
Molecular Biology Reports, 2014
The ITS region of the ribosomal RNA genes from two and six-rowed cultivated barley (Hordeum vulgare subsp. distichon and H. v. subsp. hexastichon, respectively), and its two and six-rowed wild relatives (H. v. subsp. spontaneum and H. v. subsp. agriocrithon, respectively) was isolated and sequenced. The entire ITS region is 598 bp in the two-rowed taxa (H. v. subsp. distichon and H. v. subsp. spontaneum) and 599 bp in the sixrowed ones (agriochriton and hexastichon). The ITS1 is 217 bp in the six-rowed barleys (H. v. subsp. agriochriton and H. v. subsp. hexastichon) and 218 bp in the two-rowed barleys (H. v. subsp. distichon and H. v. subsp. spontaneum). The 5.8S region is 163 bp in all studied H. vulgare taxa. The ITS2 region is 217 bp in the two-rowed barleys (H. v. subsp. distichon and H. v. subsp. spontaneum) and 219 bp in the six rowed ones (H. v. subsp. hexastichon and H. v. subsp. agriochriton). The ITS sequence data of the studied taxa and that of three other wild Hordeum species (H. murinum, H. marinum and H. chilense) were aligned and a phylogeny tree was reconstructed using the Lasergene Program. H. v. subsp. spontaneum was appeared as the ancestor of all other H. vulgare taxa.
Distribution, inheritance and linkage relationships of ribosomal DNA spacer length variants in pea
Theoretical and Applied Genetics, 1986
DNA restriction endonuclease fragment analysis is used to examine the genetic organization, inheritance and linkage associations of the ribosomal DNA in pea. The substantial variation observed in the length of the intergenic spacer region is shown to segregate in Mendelian fashion involving two independent genetic loci, designated Rrnl and Rrn2. Linkage between Rrnl and two marker loci on chromosome 4 establishes the approximate location of this tandem array. Rrn2 shows linkage with a set of isozyme loci which assort independently of other markers on all seven chromosomes. Combining these observations with previous cytological data, we suggest that Rrn2 and the isozyme loci linked to it constitute a new linkage group on chromosome 7. The general absence of spacer length classes common to both rRNA loci in any of the lines we examined indicates that little or no genetic exchange occurs between the nonhomologous nucleolar organizer regions.
Ribosomal gene structure, variation and inheritance in maize and its ancestors
Genetics, 1988
We have examined the structure of nuclear genes coding for ribosomal RNAs in maize and its wild relatives, the teosintes and Tripsacum. Digestion of the rDNA (genes coding for 18S, 5.8S and 26S RNAs) with 15 restriction endonucleases (with six base pair recognition sites) yields essentially a single map for the approximately 10,000 repeat units within an individual plant or species. Both length and site variation were detected among species and were concentrated in the intergenic spacer region of the rDNA repeat unit. This result is in agreement with patterns of rDNA change observed among wheat and its relatives (Triticeae), and among vertebrate species. Digestion of these nuclear DNAs with BamHI and subsequent hybridization with a 5S RNA gene-specific probe allowed determination of the size of the 5S gene repeat unit in maize, teosintes, and Tripsacum. Groupings in the genus Zea were characterized by distinct repeat unit types five Tripsacum species examined shared a 260 base pair ...
Extraordinarily polymorphic ribosomal DNA in wild and cultivated rice
Genome, 1996
A collection of 481 rice accessions was surveyed for ribosomal DNA (rDNA) intergenic spacer length polymorphism to assess the extent of genetic diversity in Chinese and Asian rice germplasm. The materials included 83 accessions of common wild rice, Oryza rufipogon, 75 of which were from China; 348 entries of cultivated rice (Oryza sativa), representing almost all the rice growing areas in China; and 50 cultivars from South and East Asia. A total of 42 spacer length variants (SLVs) were detected. The size differences between adjacent SLVs in the series were very heterogeneous, ranging from ca. 21 to 311 bp. The 42 SLVs formed 80 different rDNA phenotypic combinations. Wild rice displayed a much greater number of rDNA SLVs than cultivated rice, while cultivated rice showed a larger number of rDNA phenotypes. Indica and japonica groups of O. sativa contained about equal numbers of SLVs, but the SLV distribution was significantly differentiated: indica rice was preferentially associated...