Genome Evolution Due to Allopolyploidization in Wheat

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.

Hybridization of powdery mildew strains gives rise to pathogens on novel agricultural crop species

“…Our data now indicate that hybridization was the causal step in host range expansion to a newly bred or evolved species. It is apparent that coevolution based on hybridization is a likely evolutionary pathway for B. graminis that infects wheat and other grasses, which themselves evolve predominantly through hybridization 25 . It is particularly fascinating that pathogen evolution mirrors evolution on the host side and that the hybrid of two mildews specialized on two different hosts can infect the hybrid plant species originating from those two hosts (Fig.…”

The shock of being united and symphiliosis

“…[1][2][3][4][5][6][7][8] A common cause of these aberrations, according to the actively debated tetraploidy model of carcinogenesis, [9][10][11][12][13][14][15][16] is an accidental increase in ploidy. An accidental increase in ploidy is also a common and extensively studied cause of evolution in plants, 17,18 a potential homology to explore for clues to cancer development. This commentary suggests that one of these clues is the fact that the properties and the evolutionary potential of plants are defined by how they become tetraploid (Box 1).…”

“…While phenotypic manifestations of autopolyploidy may not always be obvious, 17,29 allopolyploid plants have high phenotypic plasticity, are prevalent, adapt better to challenging environments and are prone to saltational evolution. 17,18,29,32,33 "One example of rapid and superior adaptation is provided by the widespread dispersal of the invasive, recently formed allopolyploid, Spartina anglica, which contrasts with the relatively noninvasive nature of the parental species, which are presumed to be autopolyploids". 17 The properties of allopolyploid plants and the "footprints" of allopolyploidy in plant genomes led to the "diverge, merge, and diverge" model, according to which a majority of the flowering species have emerged from repeated cycles of allopolyploidy and divergence.…”

“…The list includes chromosome translocations, inversions, deletions, duplications, loss, amplification or reduction of repetitive sequences, extensive chromosome repatterning, horizontal transfer of genomic segments between the parental genomes, nonreciprocal homeologous recombination, repetitive sequences, transposon activation, and aneuploidy. 18,34,[36][37][38] At least some of the genomic rearrangements are not random and involve elimination of specific noncoding DNA sequences and intergenomic suppression of disease-resistant genes. 18 Like genomic aberrations in cancer, genomic rearrangements in allopolyploids can range from simple to highly complex, persist through generations, or re-emerge after being in remission for generations.…”

“…18,34,[36][37][38] At least some of the genomic rearrangements are not random and involve elimination of specific noncoding DNA sequences and intergenomic suppression of disease-resistant genes. 18 Like genomic aberrations in cancer, genomic rearrangements in allopolyploids can range from simple to highly complex, persist through generations, or re-emerge after being in remission for generations. 18,[34][35][36]39 However substantial the genomic restructuring is, "by far, the most striking change to regulation of gene expression in allopolyploids… is that of epigenetic modification".…”