Identifying Orthologous Regions among Aegilops tauschii, Brachypodium distachyon and Rice through Comparative Sequence Analyses.

The wild grass species Brachypodium distachyon has emerged as a new model for temperate grasses because of its small genome (C=320 Mb), short generation time and simple growth requirements. Under the current model of grass evolution, a degree of gene order conservation is expected between B. distachyon and the pooid genera which includes bread wheat (C=17,000 Mb) and the majority of cool-season grasses. However, a degree of synteny erosion is also anticipated in genomes differing significantly in size. It is therefore essential to have comparative sequence information on the extent of colinearity between B. distachyon and species of this group. We are currently conducting an extensive comparison between genome regions of Aegilops tauschii, the D genome donor of bread wheat, B. distachyon and rice in order to estimate the level of colinearity and the rate with which synteny is decreasing during genome evolution. A sequence analysis of approximately 2.5 Mb of DNA selected from chromosome 4D of Ae. tauschii has been completed, and we will report on the comparative relationship between the Ae. tauschii sequence and the corresponding orthologous sequences in B. distachyon and rice.