Rapid evolution of simple sequence repeat induced by allopolyploidization.

Microsatellite evolution normally occurs in diploids. Until now, there has been a lack of direct experimental evidence for microsatellite evolution following allopolyploidization. In the present study, F(1) hybrids and newly synthesized allopolyploids were derived from Triticum aestivum Chinese Spring x Secale cereale Jinzhou-heimai. One hundred and sixty-three wheat simple sequence repeat (SSR) markers were used to investigate the variation of wheat microsatellites after allopolyploidization and variation of the PCR products of 29 of the SSR markers was observed. Of these 29 SSR markers, 15 were unable to produce products from amphiploids. The other 14 SSR markers did produce products from parental wheat, F(1) hybrids and amphiploids. However, the length of the products amplified from amphiploids was different from the length of the products amplified from parental wheat and F(1) hybrids. Sequencing indicated that the length variation of the 14 microsatellites stemmed mainly from variation in the number of repeat units. The alteration of repeat units occurred in both perfect and compound repeats. In some compound SSR loci, one motif was observed to expand whereas another to contract. Almost all the microsatellite evolution observed in this study could be explained by the slipped-strand mispairing model. The results of this study seem to indicate that stress caused by allopolyploidization might be one of the factors that induce microsatellite evolution. In addition, the findings of present study provided an instance of how simple sequence repeats evolved after allopolyploidization.