Chromosome 'speed dating' during meiosis of polyploid Brassica hybrids and haploids.
Given their tremendous importance for correct chromosome segregation, the number and distribution of crossovers are tightly controlled during meiosis. In this review, we give an overview of crossover formation in polyploid Brassica hybrids and haploids that illustrates or underscores several aspects of crossover control. We first demonstrate that multiple targets for crossover formation (i.e. different but related chromosomes or duplicated regions) are sorted out during meiosis based on their level of relatedness. In euploid Brassica napus (AACC; 2n = 38), crossovers essentially occur between homologous chromosomes and only a few of them form between homeologues. The situation is different in B. napus haploids in which crossovers preferentially occur between homeologous chromosomes and a few can then form between more divergent duplicated regions. We then provide evidence that the frequency of crossovers between a given pair of chromosomes is influenced by the karyotypic and genetic composition of the plants that undergo meiosis. For instance, genetic evidence indicates that the number of crossovers between exactly the same pairs of homologous A chromosomes gets a boost in Brassica digenomic tetraploid (AACC) and triploid (AAC) hybrids. Increased autosyndesis within B. napus haploids as compared to monoploid B. rapa and B. oleracea is another illustration of this process. All these observations may suggest that polyploidization overall boosts up crossover machinery and/or that the number of crossovers is modulated through inter-bivalents or univalent-bivalent cross-talk effects. The last part of this review gives an up-to-date account of what we know about the genetic control of homologous and homeologous crossover formation among Brassica species.
Nicolas
S D
SD
UMR INRA-Agrocampus Rennes, Amélioration des Plantes et Biotechnologies Végétales, Le Rheu, France.
Leflon
M
M
Liu
Z
Z
Eber
F
F
Chelysheva
L
L
Coriton
O
O
Chèvre
A M
AM
Jenczewski
E
E
D001937:Brassica / Q000166:cytology* / Q000235:genetics*; D029688:Brassica napus / Q000166:cytology / Q000235:genetics; D029741:Brassica rapa / Q000166:cytology / Q000235:genetics; D023902:Chromosome Pairing; D022202:Chromosomes, Artificial, Bacterial / Q000235:genetics; D032461:Chromosomes, Plant / Q000235:genetics*; D003434:Crossing Over, Genetic; D017343:Genes, Plant; D006238:Haploidy; D006824:Hybridization, Genetic; D017404:In Situ Hybridization, Fluorescence; D008540:Meiosis / Q000235:genetics*; D008957:Models, Genetic; D011123:Polyploidy; D011995:Recombination, Genetic