Genetic And Epigenetic Stability At The Onset Of Triticum Aestivum Speciation

Allohexaploidization is a critical step leading to the formation of common wheat as a new species,Triticum aestivum L.,as well as for bestowing its remarkable adaptability. A recent study documented that allohexaploidization in wheat was associated with strikingly high degrees of both genetic and epigenetic dynamics at genomic regions flanking a retrotransposon family named Veju. Although this finding is in line with the prevailing opinion of rapid genomic restructuring associated with nascent plant allopolyploidy,its relevance to speciation of T.aestivum L. is unclear.Here,we show that genetic instability at genomic regions flanking the retrotransposon Veju,flanking a more abundant retroelement,BARE-1,as well as at a large number of randomly sampled genomic loci by the amplified fragment length polymorphism (AFLP) maker is all extremely rare or nonexistent in preselected individuals representing three sets of independently formed nascent allohexaploid wheat lines,which had a transgenerationally stable genomic constitution analogous to that of T.aestivum. In contrast, extensive and transgenerationally heritable genetic instability at randomly sampled genomic loci were detected in the fourth wheat lines which were aneuploid. And also there were large and transgenerationally heritable repatterning of DNA methylation at all three kinds of genomic loci were reproducibly detected in all the studied individuals by the corresponding methylation-sensitive markers,and validated by bisulfite genomic sequencing.To further explore possible reasons for the genetic stability but epigenetic remodeling in the form of DNA methylation in the early stage of allohexaploid wheat lines which had stable genomic constitution, q-RT-PCR were used to analyze a set of cell cycle checkpoint genes and mismatch repair genes which are known to be involved in maintaining genetic stability; and a set of genes participating in chromatin epigenetic regulation. The results showed that the expression of most of these genes were significantly upregulated in all three wheat lines relative to their diploid and tetraploid parents, suggested these changes may have played a functional role in the to genetic stability and epigenetic remodeling in the newly formed allohexaploid wheat.Take together,our results suggest that extensive and heritable epigenetic remodeling coupled with preponderance of genetic stability is generally associated with nascent allohexaploidization in wheat and therefore more likely a contributory factor to the speciation event(s).