Genomic Variation Induced By Polyploidization Of Wheat

Polyploidy is a common phenomenon in plants and some animal branches. Wideinterspecific or intergeneric hybridization, followed by chromosome doubling either beforeor after the hybridization event is one of the prominent models of speciation in higherplants. Despite their success in Nature, the initial formation of an allopolyploid must be ashock. Recent studies demonstrated that allopolyploid formation in the early stages is oftenaccompanied by genomic changes that cannot be readily explained by Mendelian geneticprinciples. Little is known, however, with respect to this sudden genetic mergers andnecessary adjustment and alteration.We analyzed the events that affect genome structure and expression in the early periodof allopolyploid in common wheat. Common wheat is not only one of the most importantstaple crops for humankind all over the world, but also a typical example of speciationthrough allopolyploidy. We addressed this issue by using materials involving a synthesizedhexapolid allopolyploid wheat in the seventh generation which has nearly identical geneticconstitution with common wheat(named XX340), the tetraploid progenitors (T. turgidumL. var. dicoccoides, named TTD09,genome AABB)and diploid progenitors (Aegilopstauschii Coss var. typical, named TQ01,genome DD),as well as the standard genotype ofnatural common wheat, i.e. Chinese Spring, taking advantage of ISSR molecular markerand so forth covering the whole genome. The result indicated that speciation ofallopolyploid wheat induced rapid and extensive genetic and epigenetic changes in thegenome. The coherence in changes between synthesized hexaploids and even betweensynthesized hexaploids and natural common wheat showed that most of genetic variationsand cytosine methylation changes did not occur randomly. It may represent a highlypreprogrammed event to cushion the effects of the shock supporting McClintock's view.Sequence analysis suggested that some encoding genes may have genetic changes.Non-random genetic and epigenetic changes tend to give rise to altered gene expressionand original phenotypic characters. As a consequence, the latter influenced by naturalselection may contribute to formation and stabilization of new species.