New insights into the organization and evolution of wheat genomes

摘要

Mapping of genes detected by wheat expressed sequence tags (ESTs) in hexaploid wheat and an analysis of distribution and frequencies of gene deletions in tetraploid and hexaploid wheats provided new insights into the organization of wheat genomes andsuggested that recombination has played a central role in their evolution. Relative gene densities and recombination rates along wheat chromosome arms were shown to increase with the relative distance from the centromere. Single-gene loci present once ineach 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 correlatedpositively with recombination rates along chromosome arms. Fixed deletions of loci that occurred in diploid ancestors of wheat were also most frequent in high recombination regions. The global effect of these trends is that the distal regions of wheat chromosomes arms have been evolving faster than the proximal, low-recombination regions. This is reflected by lower synteny between homoeologous chromosome in the distal chromosome regions than in the proximal chromosome regions. Polymorphism for deletions that occurred during the evolution of tetraploid and hexaploid wheat was higher in the distal, high-recombination region than in the proximal, 1 ow-recombination region. It is suggested that that this disparity in the deletions rates leads to higher gene density in the distal chromosome regions.