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A number of technologies are available to increase the abundance of DNA markers and contribute to developing high resolution genetic maps suitable for genetic analysis. The aim of this study was to expand the number of Diversity Array Technology (DArT) markers on the wheat array that can be mapped in the wheat genome, and to determine their chromosomal location with respect to simple sequence repeat (SSR) markers and their position on the cytogenetic map. A total of 749 and 512 individual DArT and SSR markers, respectively, were identified on at least one of four genetic maps derived from recombinant inbred line (RIL) or doubled haploid (DH) populations. A number of clustered DArT markers were observed in each genetic map, in which 20–34% of markers were redundant. Segregation distortion of DArT and SSR markers was also observed in each mapping population. Only 14% of markers on the Version 2.0 wheat array were assigned to chromosomal bins by deletion mapping using aneuploid lines. In this regard, methylation effects need to be considered when applying DArT marker in genetic mapping. However, deletion mapping of DArT markers provides a reference to align genetic and cytogenetic maps and estimate the coverage of DNA markers across the wheat genome. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is a major disease in the wheat growing regions of the world. A quantitative trait locus (QTL) on the short arm of chromosome 3B controls much of the variation for resistance. The cloning of candidate disease-resistance genes for FHB QTLs on chromosome 3B can provide further elucidation of the mechanisms that control resistance. However, rearrangements and divergence during plant genome evolution often hampers the identification of sequences with similarity to known disease-resistance genes. This study focuses on the use of wheat expressed sequence tags (ESTs) that map to the region on chromosome 3B containing the QTL for FHB resistance and low-stringency BLAST searching to identify sequences with similarity to known disease-resistance genes. One EST rich with leucine repeats and low similarity to a protein kinase domain of the barley Rpg1 gene was identified. Genetic mapping using a Ning894037 × Alondra recombinant inbred (RI) population showed that this EST mapped to the QTL on the short arm of chromosome 3B and may represent a portion of a newly diverged gene contributing to FHB resistance. The EST is a new marker suitable for marker-assisted selection and provides a starting point to begin map-based cloning for chromosome walking and investigate new diverged genes at this locus. [ABSTRACT FROM AUTHOR]

A diminutive rye chromosome (midget) in wheat was used as a model system to isolate a highly reiterated centromeric sequence from a rye chromosome. Fluorescence in situ hybridization (FISH) shows this sequence localized within all rye centromeres and no signal was detected on wheat chromosomes. DNA sequencing of the repetitive element has revealed the presence of some catalytic domains and signature motifs typical of retrotransposon genes and has been called the Bilby family, representing a diverged family of retrotransposon-like elements. Extensive DNA database searching revealed some sequence similarity to centromeric retrotransposons from wheat, barley, and centromeric repetitive sequences from rice. Very low levels of signal were observed when Bilby was used as a probe against barley, and no signal was detected with rice DNA during Southern hybridization. The abundance of Bilby in rye indicates that this family may have diverged from other distantly related centromeric retrotransposons or incorporated in the centromere but rapidly evolved in rye during speciation. The isolation of a rye retrotransposon also allowed the analysis of centromeric breakpoints in wheat-rye translocation lines. A quantitative analysis shows that the breakpoint in 1DS.1RL and 1DL.1RS and recombinant lines containing proximal rye chromatin have a portion of the rye centromere that may contribute to the normal function of the centromeric region.Key words: centromere, retrotransposon, rye, midget chromosome, cereals.Un chromosome diminutif du seigle (« midget ») a été employé chez le blé comme système modèle afin d'isoler une séquence centromérique répétitive du seigle. L'hybridation in situ en fluorescence (FISH) a montré que cette séquence est présente chez tous les centromères du seigle et aucun signal n'a été détecté chez les chromosomes du blé. L'examen de la séquence nucléotidique de cet élément répété a révélé la présence de domaines catalytiques et de motifs conservés typiques des gènes portés par les rétrotransposons. Cet élément a été nommé Bilby et il appartient à une famille d'éléments divergés ressemblant à des rétrotransposons. Des fouilles minutieuses des bases de données ont fait ressortir des similitudes avec des rétrotransposons centromériques du blé et de l'orge ainsi qu'avec des séquences centromériques répétitives chez le riz. De très faibles signaux ont été observés lorsque Bilby a été employé comme sonde chez l'orge et aucun signal n'a été décelé en hybridation Southern chez le riz. L'abondance de Bilby chez le seigle indique que cette famille pourrait avoir divergé à partir d'autres rétrotransposons centromériques ou encore avoir été incorporé dans le centromère et avoir subi une rapide évolution lors de la spéciation du seigle. L'obtention d'un rétrotransposon du seigle a également permis d'analyser les points de bris centromériques chez des lignées à translocation blé-seigle. Une analyse quantitative a montré que les cassures au sein des translocations 1DS.1RL et 1DL.1RS et au sein de lignées recombinantes portant de la chromatine proximale en provenance du seigle contiennent une portion du centromère du seigle, lequel contribue peut-être au bon fonctionnement de la région centromérique.Mots clés : centromère, rétrotransposon, seigle, chromosome nain « midget », céréales.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]