Search

Loci detected by Southern blot hybridization of 3,977 expressed sequence tag unigenes were mapped into 159 chromosome bins delineated by breakpoints of a series of overlapping deletions. These data were used to assess synteny levels along homoeologous chromosomes of the wheat A, B, and D genomes, in relation to both bin position on the centromere-telomere axis and the gradient of recombination rates along chromosome arms. Synteny level decreased with the distance of a chromosome region from the centromere. It also decreased with an increase in recombination rates along the average chromosome arm. There were twice as many unique loci in the B genome than in the A and D genomes, and synteny levels between the B genome chromosomes and the A and D genome homoeologues were lower than those between the A and D genome homoeologues. These differences among the wheat genomes were attributed to differences in the mating systems of wheat diploid ancestors. Synteny perturbations were characterized in 31 paralogous sets of loci with perturbed synteny. Both insertions and deletions of loci were detected and both preferentially occurred in high recombination regions of chromosomes.

Genes detected by wheat expressed sequence tags (ESTs) were mapped into chromosome bins delineated by breakpoints of 159 overlapping deletions. These data were used to assess the organizational and evolutionary aspects of wheat genomes. Relative gene density and recombination rate increased with the relative distance of a bin from the centromere. Single-gene loci present once in the wheat genomes were found predominantly in the proximal, low-recombination regions, while multigene loci tended to be more frequent in distal, high-recombination regions. One-quarter of all gene motifs within wheat genomes were represented by two or more duplicated loci (paralogous sets). For 40 such sets, ancestral loci and loci derived from them by duplication were identified. Loci derived by duplication were most frequently located in distal, high-recombination chromosome regions whereas ancestral loci were most frequently located proximal to them. It is suggested that recombination has played a central role in the evolution of wheat genome structure and that gradients of recombination rates along chromosome arms promote more rapid rates of genome evolution in distal, high-recombination regions than in proximal, low-recombination regions.

Rye is a diploid crop species with many outstanding qualities, and is important as a source of new traits for wheat and triticale improvement. Rye is highly tolerant of aluminum (Al) toxicity, and possesses a complex structure at the Alt4 Al tolerance locus not found at the corresponding locus in wheat. Here we describe a BAC library of rye cv. Blanco, representing a valuable resource for rye molecular genetic studies, and assess the library’s suitability for investigating Al tolerance genes. The library provides 6 × genome coverage of the 8.1 Gb rye genome, has an average insert size of 131 kb, and contains only ~2% of empty or organelle-derived clones. Genetic analysis attributed the Al tolerance of Blanco to the Alt4 locus on the short arm of chromosome 7R, and revealed the presence of multiple allelic variants (haplotypes) of the Alt4 locus in the BAC library. BAC clones containing ALMT1 gene clusters from several Alt4 haplotypes were identified, and will provide useful starting points for exploring the basis for the structural variability and functional specialization of ALMT1 genes at this locus. [ABSTRACT FROM AUTHOR]

Copyright of Genome is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Genome is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Genome is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Genome is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Genome is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Genome is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Genome is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Allopolyploidy is a prominent mode of speciation in higher plants. Due to the coexistence of closely related genomes, a successful allopolyploid must have the ability to invoke and maintain diploid-like behavior, both cytologically and genetically. Recent studies on natural and synthetic allopolyploids have raised many discrepancies. Most species have displayed non-Mendelian behavior in the allopolyploids, but others have not. Some species have demonstrated rapid genome changes following allopolyploid formation, while others have conserved progenitor genomes. Some have displayed directed, non-random genome changes, whereas others have shown random changes. Some of the genomic changes have appeared in the F1 hybrids, which have been attributed to the union of gametes from different progenitors, while other changes have occurred during or after genome doubling. Although these observations provide significant novel insights into the evolution of allopolyploids, the overall mechanisms of the event are still elusive. It appears that both genetic and epigenetic operations are involved in the diploidization process of allopolyploids. Overall, genetic and epigenetic variations are often associated with the activities of repetitive sequences and transposon elements. Specifically, genomic sequence elimination and chromosome rearrangement are probably the major forces guiding cytological diploidization. Gene non-functionalization, sub-functionalization, neo-functionalization, as well as other kinds of epigenetic modifications, are likely the leading factors promoting genetic diploidization. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Copyright of Genome is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Extended flanking DNA sequences were characterized for five members of the wheat high molecular weight (HMW) glutenin gene family to understand more of the structure, control, and evolution of these genes. Analysis revealed more sequence conservation among orthologous regions than between paralogous regions, with differences mainly owing to transposition events involving putative retrotransposons and several miniature inverted transposable elements (MITEs). Both gyspy-like long terminal repeat (LTR) and non-LTR retrotransposon sequences are represented in the flanking DNAs. One of the MITEs is a novel class, but another MITE is related to the maize Stowaway family and is widely represented in Triticeae express sequence tags (ESTs). Flanking DNA of the longest sequence, a 20 425-bp fragment including and surrounding the HMW-glutenin Bx7 gene, showed additional cereal gene-like sequences both immediately 5' and 3' to the HMW-glutenin coding region. The transcriptional activities of sequences related to these flanking putative genes and the retrotransposon-related regions were indicated by matches to wheat and other Triticeae ESTs. Predictive analysis of matrix-attachment regions (MARs) of the HMW glutenin and several α-, γ-, and ω-gliadin flanking DNAs indicate potential MARs immediately flanking each of the genes. Matrix binding activity in the predicted regions was confirmed for two of the HMW-glutenin genes.Key words: wheat, glutenins, evolution, matrix-attachment regions, transposable elements.De grandes régions d'ADN adjacentes aux cinq gènes codant pour des gluténines de poids moléculaire élevé (HMW) ont été caractérisées afin de mieux connaître la structure, la régulation et l'évolution de ces gènes. L'analyse a révélé davantage de conservation de séquences parmi les régions orthologues qu'entre les régions paralogues, les différences étant principalement attribuables à des événements de transposition impliquant des rétrotransposons putatifs et plusieurs MITE (« miniature inverted transposable elements »). Tant des rétrotransposons à LTR (« long terminal repeats ») de type gypsy que des rétrotransposons sans LTR ont été trouvés dans les séquences adjacentes. Un des MITE est d'un type nouveau tandis qu'un autre est apparenté à la famille des éléments Stowaway et se trouve dans plusieurs EST (« express sequence tags ») provenant de hordées. L'ADN adjacent au gène parmi le plus grand segment séquencé, un fragment de 20 425-pb incluant et bordant le gène codant pour la gluténine-HMW Bx7, comprenait des séquences ressemblant à des gènes de graminées. Une activité transcriptionnelle de séquences homologues à ces gènes putatifs ou aux régions apparentées à des rétrotransposons est suggérée du fait que de telles séquences ont été trouvées parmi des collections d'EST du blé et d'autres graminées. Une analyse visant à identifier des régions d'attachement à la matrice (MAR) a suggéré la présence de possibles régions MAR dans le voisinage immédiat de tous les gènes codant pour des gluténines-HMW et de plusieurs gliadines α, γ et ω. Une activité d'attachement à la matrice a été confirmée pour deux des régions MAR prédites au voisinage de gènes codant pour des gluténines-HMW.Mots clés : blé, gluténines, évolution, régions d'attachement à la matrice, éléments transposables.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Rye (Secale cereale L.) is considered to be the most aluminum (Al)-tolerant species among the Triticeae. It has been suggested that aluminum tolerance in rye is controlled by three major genes (Alt genes) located on rye chromosome arms 3RL, 4RL, and 6RS, respectively. Screening of an F6 rye recombinant inbred line (RIL) population derived from the cross between an Al-tolerant rye (M39A-1–6) and an Al-sensitive rye (M77A-1) showed that a single gene controls aluminum tolerance in the population analyzed. In order to identify molecular markers tightly linked to the gene, we used a combination of amplified fragment length polymorphism (AFLP) and bulked segregant analysis techniques to evaluate the F6 rye RIL population. We analyzed approximately 22,500 selectively amplified DNA fragments using 204 primer combinations and identified three AFLP markers tightly linked to the Alt gene. Two of these markers flanked the Alt locus at distance of 0.4 and 0.7 cM. Chromosomal localization using cloned AFLP and a restriction fragment length polymorphism (RFLP) marker indicated that the gene was on the long arm of rye chromosome 4R. The RFLP marker (BCD1230) co-segregated with the Alt gene. Since the gene is on chromosome 4R, the gene was designated as Alt3. These markers are being used as a starting point in the construction of a high resolution map of the Alt3 region in rye. [ABSTRACT FROM AUTHOR]

Powdery mildew (caused by Erysiphe graminis) and yellow rust (caused by Puccinia striiformis) are the two most serious wheat diseases found in China. Rye chromosomes, carrying genes for resistance to these diseases, were introduced into common wheat in two generations using chromosome engineering and anther culture. The F1 hybrids from a cross involving a hexaploid triticale (× Triticosecale Wittmack) × ‘Chinese Spring’ nulli-tetrasomic N6DT6A wheat aneuploid line were anther cultured and doubled-haploid plants were regenerated. Using genomic in situ hybridization, C-banding and biochemical marker analyses, one of the anther-cultured lines (ZH-1)studied in detail, proved to be a doubled-haploid with one rye chromosome pair added (1R) and a homozygous 6R/6D substitution (2n = 44). The line was tested for expression of disease resistance and found to be highly resistant to powdery mildew and moderately resistant to yellow rust. [ABSTRACT FROM AUTHOR]

The influence of telomeric heterochromatin on early embryo and endosperm development and the production of aberrant endosperm nuclei were investigated using eight triticale (× Tritocosecale Wittmack) lines homozygous for the presence or absence of blocks of telomeric heterochromatin from rye chromosome arms 1RL, 2RS, 6RS, and 7RL. The loss of heterochromatin from two chromosomes (6R, 7R) produced a significantly lower percentage of aberrant endosperm nuclei than did the loss form one chromosome (6R). Deletion of a third block had a significant additional effect in only one of four lines. The differences between lines for rates of embryo and endosperm development were significant even within a karyotype, presumably because of genetic variation. the onset of cellularization of the endosperm tended to obscure the detection of aberrancy, and since it evidently occurred at different times in different lines, may have been largely responsible for the apparent reduction in aberrant nuclei in lines with less heterochromatin. [ABSTRACT FROM AUTHOR]