Genomic plasticity in polyploid wheat

The importance of hybridization and polyploidization in wheat speciation has been recognized for close to a century (Sakamura 1918; Kihara 1919, 1924, 1954; Percival 1921; Sax 1927). Following these pioneering works, it quickly became apparent that polyploid wheats are not the sum of their constituent genomes. This is not unexpected because the nascent hybrids/polyploids are equipped with a complex set of regulatory elements and of copy number variation that originate from two or more divergent genomes and that generate novel types of interactions and dosage effects. Moreover, they have to adjust at the cytological level, at the level of gene expression, and at the protein level. They also have to maintain genome stability through the regulation of meiotic pairing and recombination, the orchestration of cell division, and the silencing of transposons. The recent studies described here provide an impressive account with regard to the extent and the rapid time course at which a new genetic variant was established upon hybridization and polyploidization. We describe here the current knowledge on the changes that occurred in the wheat genome upon allopolyploidization, starting from the early evolutionary and cytological studies to the recent genomic analyses.