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Thesis started november 1st, 2013 - Defended in november 10^th 2016
Fund: INRA/Region Bretagne
Direction: Anne-Marie Chèvre

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Abstract:

Meiotic homologous recombination by crossovers (COs) is the main mechanism responsible for mixing genetic diversity in plant breeding. However, loci separations are limited due to the strict regulation of the rates and distribution of COs along the chromosomes. On Brassica model, allotriploid hybrids (AAC, 2n=3x=29), resulting from crosses between Brassica napus (AACC, 2n=4x=38) and B. rapa (AA, 2n=2x=20), exhibits far more COs between homologous A chromosomes compared to diploid hybrids (AA, 2n=2x=20) and allotetraploid hybrids (AACC, 2n=4x=38). The objective of the thesis was to determine the impact of such a boost of CO rate on recombination landscapes along the A chromosomes. Additionally, the effect of genome evolution, sex of meiosis and specific C chromosomes involved in such regulation was deciphered. After cytogenetic analyses, the recombination frequencies and landscapes were evaluated from large progenies of F1 hybrids, presenting different karyotypes, by a genotyping approach using SNP markers anchored on the whole A genome. We always showed that the additional C genome in allotriploids dramatically reshapes the recombination landscapes with the formation of new recombining regions in the vicinity of centromeres, usually devoid of COs, associated with a strong decrease of CO interference. Additionally, we determined in AAC hybrids that the sex of meiosis is a key factor regulating the number of extra-COs formed. Finally, we highlighted that the genetic control of these variations is mainly due to the addition of the C09 chromosome when it comes from the cabbage B. oleracea. In contrast, in natural rapeseed B. napus, this control could have diverged in a polyploid context. From all these results, we showed that it is possible to generate new allelic combination in rapeseed by breaking the linkage disequilibrium using allotriploid hybrids. Additionally, we identified different key factors regulating these variations.