Chromosomal and genome-wide molecular changes associated with initial stages of allohexaploidization in wheat can be transit and incidental.

Genomic instability can be induced by nascent allopolyploidization in plants. However, most previous studies have not defined to what extent the allopolyploidy-induced rapid genomic instability represents a general response, and hence important to evolution, or merely incidental events occurring stochastically in a limited number of individuals. We report here that in a newly formed allohexaploid wheat line between tetraploid wheat Triticum turgidum subsp. durum (genome BBAA) and Aegilops tauschii (genome DD) a great majority of individual plants showed chromosomal stability and exhibited a genomic constitution similar to that of the present-day Triticum aestivum (genome BBAADD). In contrast, a single individual plant was identified at S-2, which exhibited chromosomal instability in both number and structure based on multicolor genomic in situ hybridization (mc-GISH) analysis. Accordingly, this plant also manifested extensive changes at the molecular level including loss and gain of DNA segments and DNA methylation repatterning. Remarkably, the chromosomal and molecular instabilities that presumably occurred at So to Si and (or) in the F-1 hybrid were rapidly quenched by S2 and followed by stable transgenerational inheritance. Our results suggest that these stochastic and individual-specific rapid genomic changes, albeit interesting, probably have not played a major role in the speciation and evolution of common wheat, T aestivum.