Analysis of a contiguous 211 kb sequence in diploid wheat (Triticum monococcum L.) reveals multiple mechanisms of genome evolution

In plant species with large genomes such as wheat or barley, genome organiz ation at the level of DNA sequence is largely unknown. The largest sequence s that are publicly accessible so far from Triticeae genomes are two 60 kb and 66 kb intervals from barley. Here, we report on the analysis of a 211 k b contiguous DNA sequence from diploid wheat (Triticum monococcum L.). Five putative genes were identified, two of which show similarity to disease re sistance genes. Three of the five genes are clustered in a 31 kb gene-enric hed island while the two others are separated from the cluster and from eac h other by large stretches of repetitive DNA. About 70% of the contig is co mprised of several classes of transposable elements. Ten different types of retrotransposons were identified, most of them forming a pattern of nested insertions similar to those found in maize and barley. Evidence was found for major deletion, insertion and duplication events within the analysed re gion, suggesting multiple mechanisms of genome evolution in addition to ret rotransposon amplification. Seven types of foldback transposons, an element class previously not described for wheat genomes, were characterized. One such element was found to be closely associated with genes in several Triti ceae species and may therefore be of use for the identification of gene-ric h regions in these species.