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      Genome Evolution Due to Allopolyploidization in Wheat

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      Genetics
      Genetics Society of America

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          Abstract

          The wheat group has evolved through allopolyploidization, namely, through hybridization among species from the plant genera Aegilops and Triticum followed by genome doubling. This speciation process has been associated with ecogeographical expansion and with domestication. In the past few decades, we have searched for explanations for this impressive success. Our studies attempted to probe the bases for the wide genetic variation characterizing these species, which accounts for their great adaptability and colonizing ability. Central to our work was the investigation of how allopolyploidization alters genome structure and expression. We found in wheat that allopolyploidy accelerated genome evolution in two ways: (1) it triggered rapid genome alterations through the instantaneous generation of a variety of cardinal genetic and epigenetic changes (which we termed "revolutionary" changes), and (2) it facilitated sporadic genomic changes throughout the species' evolution (i.e., evolutionary changes), which are not attainable at the diploid level. Our major findings in natural and synthetic allopolyploid wheat indicate that these alterations have led to the cytological and genetic diploidization of the allopolyploids. These genetic and epigenetic changes reflect the dynamic structural and functional plasticity of the allopolyploid wheat genome. The significance of this plasticity for the successful establishment of wheat allopolyploids, in nature and under domestication, is discussed.

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          Most cited references81

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          Stomatal size in fossil plants: evidence for polyploidy in majority of angiosperms.

          Three published estimates of the frequency of polyploidy in angiosperms (30 to 35 percent, 47 percent, and 70 to 80 percent) were tested by estimating the genome size of extinct woody angiosperms with the use of fossil guard cell size as a proxy for cellular DNA content. The inferred chromosome numbers of these extinct species suggest that seven to nine is the primitive haploid chromosome number of angiosperms and that most angiosperms (approximately 70 percent) have polyploidy in their history.
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            Transcriptional activation of retrotransposons alters the expression of adjacent genes in wheat.

            Retrotransposons are a principal component of most eukaryotic genomes, representing roughly 40% of the human genome and 50-80% of some grass genomes. They are usually transcriptionally silent but can be activated under certain stresses. Despite their considerable contribution to genome structure, their impact on the expression of adjacent genes is not well understood. The steady-state transcript levels originating from Wis 2-1A retrotransposons are much higher in newly synthesized wheat amphiploids (two or more diverged genomes in the same nucleus). On activation, both Wis 2-1A long terminal repeats drive the readout synthesis of new transcripts from adjacent sequences including the antisense or sense strands of known genes. Here we report that activation of these antisense or sense transcripts is associated with silencing or activation of the corresponding genes, respectively. These data, together with the abundance of retrotransposons in genomes and their ability to be activated by various signals, support the view of transposons as potential controlling elements.
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              Genetic Control of the Cytologically Diploid Behaviour of Hexaploid Wheat

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                Author and article information

                Journal
                Genetics
                Genetics
                Genetics Society of America
                0016-6731
                1943-2631
                November 07 2012
                November 2012
                November 07 2012
                November 2012
                : 192
                : 3
                : 763-774
                Article
                10.1534/genetics.112.146316
                3522158
                23135324
                46d3c3f6-4639-4210-a971-648b48d5de88
                © 2012
                History

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