Meiotic and genomic clues into the stabilization of wheat polyploids

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Mestiri, Imen | Chague, Veronique | Huneau, Cécile, C. | Tanguy, Anne-Marie, A.-M. | Huteau, Virginie | Coriton, Olivier, O. | Jahier, Joseph, J. | Chalhoub, Boulos

Edité par CCSD -

National audience. In order to understand key mechanisms leading to stabilized allopolyploid species, we characterized the meiotic behaviour of wheat polyploids in relation to structural and genetic changes. For that purpose, we analyzed first generations of synthetic wheat allopolyploids obtained through interspecific hybridization, followed by chromosome doubling, between several genotypes of Triticum and Aegilops wheat species. These synthetic wheat allopolyploids can be divided in two main types: - Synthetic allohexaploids that were obtained through interspecific hybridization, followed by spontaneous chromosome doubling, between several genotypes of T. turgidum and Ae. tauschii wheat species, donors of AB and D genomes respectively. They are similar to natural bread hexaploid wheat and carry the Ph1 (Pairing homoeologous 1) locus that restrict pairing to homologous chromosomes during meiosis. -Synthetic allotetraploids derived from cross hybridization involving 8 diploid species from Triticum and Aegilops genera and thus representing several possible combinations of A, D and S genomes. These are not known to contain the Ph1 gene. Meiotic stability of both allotetraploids and allohexaploids was shown to depend on their genomic combination although they do not behave similarly. As expected in the Ph1 gene-carrying allohexaploids, chromosome pairing at metaphase I stage of meiosis essentially occurs between homologous chromosomes. However, the synthetic allohexaploids exhibited progenitor-dependent meiotic irregularities, such as incomplete homologous pairing, resulting in univalent formation and leading to aneuploidy in the subsequent generation. On the opposite, various levels of homoeologous pairing were evidenced in interspecific haploid hybrids and doubled allotetraploids that do not contain the Ph1 gene. Allotetraploids combining A and D genomes displayed higher level of homoeologous pairing whereas it was lower in allotetraploids combining A and S genomes. Translocation events, triggered by homoeologous recombination, were observed in synthetic allotetraploids such as those combining the A and D genomes while they were absent in synthetic allohexaploids. Aneuploidy represents a major structural changes observed in both synthetic allotetaploids and allohexaploids while no or few apparent DNA sequence elimination or rearrangement were observed when analyzing euploid plants with molecular markers, developed from expressed as well as SSR and transposable elements sequences. Relationship between regular chromosome pairing and the occurrence of structural changes and their impacts on the overall stabilization of the polyploidy species will be discussed.

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