Allopolyploidy-Induced Rapid Genome Evolution in the Wheat (Aegilops-Triticum) Group

Abstract

To better understand genetic events that accompany allopolyploid formation, we studied the rate and time of elimination of eight DNA sequences in F1 hybrids and newly formed allopolyploids of Aegilops and TRITICUM: In total, 35 interspecific and intergeneric F1 hybrids and 22 derived allopolyploids were analyzed and compared with their direct parental plants. The studied sequences exist in all the diploid species of the Triticeae but occur in only one genome, either in one homologous pair (chromosome-specific sequences [CSSs]) or in several pairs of the same genome (genome-specific sequences [GSSs]), in the polyploid wheats. It was found that rapid elimination of CSSs and GSSs is a general phenomenon in newly synthesized allopolyploids. Elimination of GSSs was already initiated in F1 plants and was completed in the second or third allopolyploid generation, whereas elimination of CSSs started in the first allopolyploid generation and was completed in the second or third generation. Sequence elimination started earlier in allopolyploids whose genome constitution was analogous to natural polyploids compared with allopolyploids that do not occur in nature. Elimination is a nonrandom and reproducible event whose direction was determined by the genomic combination of the hybrid or the allopolyploid. It was not affected by the genotype of the parental plants, by their cytoplasm, or by the ploidy level, and it did not result from intergenomic recombination. Allopolyploidy-induced sequence elimination occurred in a sizable fraction of the genome and in sequences that were apparently noncoding. This finding suggests a role in augmenting the differentiation of homoeologous chromosomes at the polyploid level, thereby providing the physical basis for the diploid-like meiotic behavior of newly formed allopolyploids. In our view, this rapid genome adjustment may have contributed to the successful establishment of newly formed allopolyploids as new species.

The effect of different genome and cytoplasm on meiotic pairing in maize newly synthetic polyploids

“…Genome organization and cytoplasm background have a significant influence on genome instability in allopolyploids (Cheung et al 2009, De Storme andGeelen 2013). During wheat polyploidization process, the genome tends to lose specific low copy sequences from D genome, which shows parental tendency and inherent difference of parent genome stability (Ozkan et al 2001). Similar phenomenon is observed in synthetic brassica hybrids, comparing with A and C genome, B genome has more stable and less pairing variation (Cui et al 2012).…”

Construction and characterization of a half million clone BAC library of durum wheat (Triticum turgidum ssp. durum)

“…Polyploidization is a dynamic process playing an important role in the evolution of plants (Soltis and Soltis 1995;Wendel 2000). Rapid genomic changes, including elimination of DNA sequences, activation of transposons, gene silencing and methylation changes, have been observed after the formation of new polyploid species (Comai et al 2000;Wendel 2000;Ozkan et al 2001;Shaked et al 2001). Comparison of BACs from the A genome of the Langdon BAC library with colinear regions from the A genome of diploid wheat species will provide additional insights into the nature and extent of these processes.…”

Gene copy number evolution during tetraploid cotton radiation

“…These reactions include loss and restructuring of low-copy DNA sequences (Song et al, 1995;Feldman et al, 1997;Ozkan et al, 2001Ozkan et al, , 2002Shaked et al, 2001;Kashkush et al, 2002), activation of genes and retrotransposons (O'Neill et al, 2002;Kashkush et al, 2003), gene silencing (Chen and Pikaard, 1997a, b;Comai et al, 2000;Lee and Chen, 2001), and subfunctionalization of gene expression patterns (Adams et al, 2003(Adams et al, , 2004Samuel Yang et al, 2006;Hovav et al, 2008). These responses are closely paralleled in animals by inactivation (Lee and Jaenisch, 1997;Avner and Heard, 2001) and differential regulation of X-chromosome gene expression (Disteche et al, 2002;Parisi et al, 2003) and retroelement activation (O'Neill et al, 2002).…”