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Thesis started november 1st, 2018 - Defended june 13^th 2022
Funding: Région Bretagne - Agrocampus Ouest
Direction: Anne-Marie Chèvre, M. Rousseau

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Abstract:

Meiotic recombination is a key evolutionary process, allowing both the correct segregation of chromosomes and the reshuffling of alleles at each generation during meiosis. Therefore, this process is highly regulated. Interestingly, Brassica AAC allotriploid hybrids (2n=3x=29), deriving from the natural cross between the allotetraploid Brassica napus (AACC, 2n=4x=38) and the diploid Brassica rapa (AA, 2n=2x=20), presents a modified recombination landscape, with more crossovers (COs) all along the genome compared to B. rapa. Additionally, they also present a modified distribution, with the presence of COS in the normally cold pericentromere regions. However, the underlying causes of this modified recombination landscape remain to be deciphered. Using a combination of genetic mapping and cytogenetic approaches, we demonstrated that the modified recombination landscape is directly linked to the AAC genomic structure compared to a AA diploid or a AACC allotetraploid. This phenotype may either be conserved in the second generation by maintaining the AAC, whereas it is reversed when reverting to a AACC genomic structure. However, some genomic regions remain deprived of recombination. We demonstrated that DNA methylation and structural variations such as chromosomal inversions are limiting factors of recombination in Brassica napus. Chromosomal inversion prevent the formation of COs within these regions, even in the highly recombining AAC hybrids. Overall, the AAC allotriploid hybrids may enable to unravel novel mechanisms regulating COs landscape. They also are particularly interesting for breeders, as they will allow to speeding up breeding programs by facilitating the introduction of traits of interest or the access of some underexploited genomic regions such as pericentromeres.

Poster.pdf