Genomic Redundancy in Young Polyploids: Does It Play an Important Role in Adaptation?

Wheat is a young allohexaploid species that, in spite of the dramatic loss of genetic diversity associated with recent domestication and polyploidization, demonstrates ability to grow in diverse eco-geographic habitats. Here we combine the multiple lines of evidence in attempt to understand the genetic and molecular basis of this broad adaptability. Analysis of gene expression showed that the majority (>80%) of duplicated genes in wheat are expressed and based on the results of chemically-induced mutagenesis experiments are functionally active. Experiments involving artificially synthesized wheat polyploids and reconstituted tetraploids suggest that the interaction between the diverged ancestral genomes in newly formed allopolyploids can generate new functional variation contributing to increased vigor and fertility. We showed that selection is relaxed in polyploid wheat resulting in accelerated accumulation of nonsynonymous mutations, structural re-arrangements and the origin of new alternative transcript isoforms. By analyzing high-density genotyping data we identified hundreds of genomic regions showing the evidence of selection likely associated with the development of locally adapted varieties. Comparison of syntenic regions among the duplicated wheat genomes showed little overlap between the targets of selection suggesting that different homoeologous copies of genes contributed adaptive alleles. We hypothesize that the ability of young allopolyploids to adapt to a broad range of environments results from new interactions established between the homoeologous copies of genes, ability to utilize allelic diversity captured from several diploid ancestors, and the exploitation of new functional variation generated at an increased rate.