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Multiple mechanisms limit meiotic crossovers

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Meiotic crossovers (COs) have two important roles, shuffling genetic information and ensuring proper chromosome segregation. Despite their importance and a large excess of precursors (i.e DNA double strand-breaks, DSBs), the number of meiotic COs is tightly regulated, typically one to three per chromosome pair [1]. Nevertheless, the mechanisms that ensure DSBs repair mostly as non-crossovers, and the evolutionary forces that impose this constraint, are poorly understood. Following a specific genetic screen, we identified several proteins that antagonize crossover formation in Arabidopsis Thaliana. This includes very conserved proteins such the helicase FANCM and its two co-factors MHF1 and MHF2 [2,3], the BLM -like helicases, the TOPOISOMERAS E3a (TOP3α) [4] and the AAA -ATPase FIDGETIN -LIKE1. Strikingly, the concomitant disruption of several of these activities led to a nine fold increase in CO frequency, without affecting chromosome segregation and fertility. This shows that several parallel pathways actively limit CO formation and supports the idea that crossover number is restricted not because of mechanical constraints but likely because of long-term costs of recombination. Furthermore, this demonstrates how manipulating a few genes holds great promise for increasing recombination frequency in plant breeding programs.

1. Mercier R, Mézard C, Jenczewski E, Macaisne N, Grelon M (2014) The Molecular Biology of Meiosis in Plants. Annu Rev Plant Biol 66: 1–31.

2. Girard C, Crismani W, Froger N, Mazel J, Lemhemdi A, Horlow C, Mercier R (2014) FANCM -associated proteins MHF1 and MHF2 , but not the other Fanconi anemia factors, limit meiotic crossovers. Nucleic Acids Res 42: 9087–9095.

3. Crismani W, Girard C, Froger N, Pradillo M, Santos JL, Chelysheva L, Copenhaver GP, Horlow C, Mercier R (2012) FANCM Limits Meiotic Crossovers. Science 336: 1588–1590.

4. Séguéla-Arnaud M, Crismani W, Larchevêque C, Mazel J, Froger N, Choinard S, Lemhemdi A, Macaisne N, Van Leene J, Gevaert K, et al. (2015) Multiple mechanisms limit meiotic crossovers: TOP3 α and two BLM homologs antagonize crossovers in parallel to FANCM . Proc Natl Acad Sci 201423107.

This talk is part of the Plant Sciences Departmental Seminars series.

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