Genome evolution in allopolyploid wheat--a revolutionary reprogramming followed by gradual changes.

Allopolyploidy accelerates genome evolution in wheat in two ways: 1) allopolyploidization triggers rapid genome alterations (revolutionary changes) through the instantaneous generation of a variety of cardinal genetic and epigenetic changes, and 2) the allopolyploid condition facilitates sporadic genomic changes during the life of the species (evolutionary changes) that are not attainable at the diploid level. The revolutionary alterations, occurring during the formation of the allopolyploid and leading to rapid cytological and genetic diploidization, facilitate the successful establishment of the newly formed allopolyploid in nature. On the other hand, the evolutionary changes, occurring during the life of the allopolyploids, increase the intra-specific genetic diversity, and consequently, increased fitness, adaptability and competitiveness. These phenomena, emphasizing the dynamic plasticity of the allopolyploid wheat genome with regards to both structure and function, are described and discussed in this review.