Macrosynthenic Relationships Between the U-, M-, S- and C-Genome Chromosomes of Aegilops and Wheat As Revealed By COS Markers

Aegilops species played a central role in the evolution of wheat and are attractive sources of traits such as yield, quality and tolerance against biotic and abiotic stress. Genes can be introduced from wild relatives to wheat by introgressive hybridization. However, the efficacy of chromosome-mediated gene transfer to wheat remains low, largely due to poor knowledge of genome structure of Aegilops and due to shortage of cost-effective molecular markers specific for Aegilops chromosomes. The conserved orthologous set markers (COS) specific for genes, which were conserved during the evolution in both sequence and copy number, are useful to compare genome structure of related species. In this work we purified by flow cytometry separate chromosomes from diploid species Ae. umbellulata (UU), Ae. comosa (MM), Ae. speltoides (SS) and Ae. caudata (CC) and compared their structure with chromosomes of wheat by identifying orthologous chromosomal regions using COS markers. The linear order of bin-mapped COS markers along the wheat D-genome chromosomes was established by the use of chromosome shotgun data and virtual gene order. Syntenic regions of wheat identifying genome rearrangements differentiating the U, M, S and C genomes from the D genome of wheat were detected. COS markers assigned to Aegilops chromosomes promise to accelerate gene introgression by providing elegant means for alien chromatin identification. The syntenic relationships between the Aegilops species and wheat will facilitate targeted development of new markers specific for U, M, S and C-genome regions and will contribute to the understanding of molecular processes underlying the evolution of Aegilops.