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Theses

Manipulation de la recombinaison chez une plante cultivée, le riz

Abstract : Manipulation of recombination in a crop, rice.The forecasted increase of world population as well as the consequences of global climate change oblige plant breeders to develop new varieties that are both more productive and resilient. Novel combinations of favourable alleles are generated through genetic recombination between homologous chromosomes, which occurs during the prophase of the first division of meiosis. Recent advances in the model plant Arabidopsis have demonstrated that the inactivation of some genes allows meiosis manipulation resulting in either an abolishment or in contrast, a significant enhancement of meiotic recombination. The meiosis mechanisms being relatively conserved across eucaryotes, the overall objective of this thesis was to transfer these advances to a crop of crucial importance, rice. To abolish meiotic recombination would allow the clonal propagation by seeds of F hybrids, which exhibit a 20% yield enhancement compared to that of pure lines in rice but remain rarely used in subsistence farming. In a first part, we showed that rice plants cumulating 3 mutations inactivating Ososd1, pair1 and Osrec8, formed clonal diploid male and female gametes. This apomeiotic phenotype, called MiMe (Mitosis instead of meiosis) in Arabidopsis, can serve as material to assay several strategies of parthenogenetic induction that would result in seed forming diploid clonal plants. Further optimization of the mechanisms would allow the use of apomixis to fix heterosis in hybrid seeds. Global and local enhancement of recombination is another desirable goal since it would allow a reduction in breeding population size and a downsizing of the introgressed chromosomal segments in elite plant materials. In a second part, we showed that mutation in the DNA helicase gene OsRECQl4 conducted to a 3.3 fold increase of recombination and inflated the genetic map size from de 1670 cM to 5538 cM, without altering plant fertility nor meiosis progression. Plants altered in a second DNA helicase, OsFANCM, exhibited a more modest 2.2 fold recombination enhancement. Recombination increase operated along the whole chromosome arms except at the centromere level. These results confirms the negative regulator role of RECQ4 and FANCM on crossing overs (CO), previously reported in Arabidopsis. On going combination of these mutations together with that altering the l’AAA-ATPase FIGL1 should conduct to an even higher recombination enhancement. These results pave the way to the use of anti-CO genes to enhance recombinant recovery in crosses of rice and possibly of other cereals. To provide breeders with a workable anti-CO system, we eventually showed that the CRISPR/Cas9 technology can be used to abolish OsFANCM, OsRECQl4 and OsFIGL1 expression.
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  • HAL Id : tel-01842247, version 1

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Delphine Mieulet. Manipulation de la recombinaison chez une plante cultivée, le riz. Sciences agricoles. Montpellier SupAgro, 2017. Français. ⟨NNT : 2017NSAM0031⟩. ⟨tel-01842247⟩

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