Submitted to: Wheat Genetics International Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/30/2003
Publication Date: 9/1/2003
Citation: Dvorak, J., Akhunov, E.D., Akhunov, A.R., Luo, M.C., Linkiewicz, A.M., Dubcovsky, J., Hummel, D., Lazo, G.R., Chao, S., Anderson, O.D. 2003. New insights into the organization and evolution of wheat genomes. Wheat Genetics International Symposium Proceedings. 1:247-253. Interpretive Summary: Recent findings about the placement of genes expressed in wheat are providing an insight into the organization of the wheat genome. Genes in wheat were tentatively placed on genetic maps constructed from a complex series of screenings against mapping lines. In the assessment of the locations of the mapped gene candidates, it appeared that there was a higher density of loci present at the ends of the chromosome arms and that fewer were located near the centromere. Within high density gene regions, duplications of some genes appeared more frequently. Those loci which appeared to represent single copy genes were more often found nearer to proximal centromeric regions. These findings point to the potential in the genome for genetic recombination to occur and may provide some additional insight toward evolution within the species.
Technical Abstract: Mapping of genes detected by wheat ESTs in hexaploid wheat and an analysis of distributions and frequencies of gene deletions in tetraploid and hexaploid wheats provided new insights into the organization of wheat genomes suggesting that recombination played a central role in their evolution. Relative gene densities and recombination rates along chromosome arms were shown to increase with the relative distance from the centromere. Single-gene loci present once in each wheat genome were located predominantly in the proximal, low-recombination regions, while multi-gene loci were more frequent in distal, high-recombination regions. The distribution of loci that originated by duplication and transposition correlated positively with recombination rates along chromosome arms. Fixed deletions that occurred in diploid ancestors of wheat were also most frequent in high recombination regions. The global effect of these trends is that distal regions of wheat chromosomes arms have been evolving faster than the proximal, low recombination regions. This is reflected by lower synteny between homoelogous chromosome in the distal chromosome regions than in the proximal chromosome regions. Polymorphism for deletions during the evolution of tetraploid and hexaploid wheat was higher in the distal, high-recombination region than in the proximal, low recombination region. It is suggested that this disparity in the deletion rates leads to higher gene density in the distal chromosome regions.