Genome Comparisons Reveal a Dominant Mechanism of Chromosome Number Reduction in Grasses and Accelerated Genome Evolution in Triticeae

Authors: LUO, M - University Of California; DEAL, K - University Of California; AKHUNOV, E - Kansas State University; AKHUNOVA, A - Kansas State University; Anderson, Olin; ANDERSON, J - University Of Minnesota; BLAKE, N - Montana State University; CLEGG, M - University Of California; COLEMAN-DERR, DEVIN - University Of California; CONLEY, E - University Of Minnesota; CROSSMAN, CURT - University Of California; DUBCOVSKY, J - University Of California; GILL, B - Kansas State University; Gu, Yong; HADAM, J - Kansas State University; HEO, H - University Of California; HUO, NAXIN - University Of California; Lazo, Gerard; LUNDY, K - University Of California; MA, Y - University Of California; Matthews, David; MCGUIRE, P - University Of California; MORRELL, P - University Of Minnesota; NICOLET, C - University Of California; QUALSET, C - University Of California; RENFRO, J - University Of California; TABANO, D - University Of California; TALBERT, L - Montana State University; TIAN, A - University Of California; TOLENO, D - University Of Minnesota; WARBURTON, M - University Of California; YOU, F - University Of California; ZHANG, W - University Of California; DVORAK, J - University Of California

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2009
Publication Date: 8/27/2009
Citation: Luo, M.C., Deal, K.R., Akhunov, E.D., Akhunova, A.R., Anderson, O.D., Anderson, J.A., Blake, N., Clegg, M.T., Coleman-Derr, D., Conley, E.E., Crossman, C.C., Dubcovsky, J., Gill, B.S., Gu, Y.Q., Hadam, J., Heo, H., Huo, N., Lazo, G.R., Lundy, K.E., Ma, Y., Matthews, D.E., Mcguire, P.E., Morrell, P.L., Nicolet, C.M., Qualset, C.O., Renfro, J., Tabano, D., Talbert, L.E., Tian, A., Toleno, D.M., Warburton, M.L., You, F.M., Zhang, W.J., Dvorak, J. 2009. Genome Comparisons Reveal a Dominant Mechanism of Chromosome Number Reduction in Grasses and Accelerated Genome Evolution in Triticeae. Proceedings of the National Academy of Sciences. 106:15780-15785.

Interpretive Summary: Using a new class of high-throughput and cost effective molecular markers, we created an extensive genetic map of one of the diploid ancestors of modern bread wheat (Aegilops tauschii). Using a diploid allows the use of many genetic tools and resources that cannot be easily manipulated in a hexaploid like breadwheat. The new map allows comparative mapping of wheat, and we have demonstrated the evolutionary process that has led to the current structure of the wheat genome. This information is of extreme importance in understanding the evolution of one of our most important crop plants, as well as illuminates paths for new wheat improvement projects.

Technical Abstract: Single nucleotide polymorphism was employed in the construction of a high-resolution, expressed sequence tag (EST) map of Aegilops tauschii, the diploid source of the wheat D genome. Comparison of the map with the rice and sorghum genome sequences revealed 50 inversions and translocations; 2, 8, and 40 were assigned respectively to the rice, sorghum, and Ae. tauschii lineages, showing greatly accelerated genome evolution in the large Triticeae genomes. The reduction of the basic chromosome number from 12 to 7 in the Triticeae is shown to have taken place by insertional dysploidy. In this process, an entire chromosome is inserted by its telomeres into a break in the centromeric region of another chromosome. The original centromere-telomere polarity of the chromosome arms is maintained in the new chromosome. In some instances, intrachromosomal telomere-telomere fusions resulting in a pericentric translocation of a chromosome segment or an entire arm accompany or precede the ch! romosome insertion. Insertional dysploidy has been recorded in three grass subfamilies and appears to the dominant mechanism of basic chromosome number reduction in grasses. A total of 64 and 66% of Ae. tauschii genes were syntenic with sorghum and rice genes, respectively. Synteny was reduced in the vicinity of the termini of modern Ae. tauschii chromosomes but not in the vicinity of the ancient termini embedded in the Ae. tauschii chromosomes by insertional dysploidy, suggesting that the dependence of synteny erosion on gene location along the centromere-telomere axis either evolved recently in the Triticeae phylogenetic lineage or its evolution was recently accelerated.