title: Repeated polyploidy drove different levels of crossover suppression between homoeologous chromosomes in Brassica napus allohaploids.
abstract: Allopolyploid species contain more than two sets of related chromosomes (homoeologs) that must be sorted during meiosis to ensure fertility. As polyploid species usually have multiple origins, one intriguing, yet largely underexplored, question is whether different mechanisms suppressing crossovers between homoeologs may coexist within the same polyphyletic species. We addressed this question using Brassica napus, a young polyphyletic allopolyploid species. We first analyzed the meiotic behavior of 363 allohaploids produced from 29 accessions, which represent a large part of B. napus genetic diversity. Two main clear-cut meiotic phenotypes were observed, encompassing a twofold difference in the number of univalents at metaphase I. We then sequenced two chloroplast intergenic regions to gain insight into the maternal origins of the same 29 accessions; only two plastid haplotypes were found, and these correlated with the dichotomy of meiotic phenotypes. Finally, we analyzed genetic diversity at the PrBn locus, which was shown to determine meiotic behavior in a segregating population of B. napus allohaploids. We observed that segregation of two alleles at PrBn could adequately explain a large part of the variation in meiotic behavior found among B. napus allohaploids. Overall, our results suggest that repeated polyploidy resulted in different levels of crossover suppression between homoeologs in B. napus allohaploids.
authors.affiliation: Institut Jean-Pierre Bourgin, Unité Mixte de Recherche 1318, INRA-AgroParisTech. Bâtiment 7, Institut National de Recherche Agronomique Centre de Versailles-Grignon, 78026 Versailles Cedex, France.
authors.forename: Marta
authors.initials: M
authors.lastname: Cifuentes
authors.forename: Frédérique
authors.initials: F
authors.lastname: Eber
authors.forename: Marie-Odile
authors.initials: MO
authors.lastname: Lucas
authors.forename: Maryse
authors.initials: M
authors.lastname: Lode
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Chèvre
authors.forename: Eric
authors.initials: E
authors.lastname: Jenczewski
mesh_terms: D029688:Brassica napus / Q000166:cytology / Q000235:genetics*; D032461:Chromosomes, Plant; D003434:Crossing Over, Genetic; D006238:Haploidy; D008540:Meiosis; D011123:Polyploidy