Frequent nonreciprocal translocations in the amphidiploid genome of oilseed rape (Brassica napus)

Abstract

A RFLP map of Brassica napus, consisting of 277 loci arranged in 19 linkage groups, was produced from genetic segregation in a combined population of 174 doubled-haploid microspore-derived lines. The integration of this map with a B. napus map derived from a resynthesized B. napus x oilseed rape cross allowed the 10 linkage groups of the B. napus A genome and the 9 linkage groups of the C genome to be identified. Collinear patterns of marker loci on different linkage groups suggested potential partial homoeologues. RFLP patterns consistent with aberrant chromosomes were observed in 9 of the 174 doubled-haploid lines. At least 4 of these lines carried nonreciprocal, homoeologous translocations. These translocations were probably the result of homoeologous recombination in the amphidiploid genome of oilseed rape, suggesting that domesticated B. napus is unable to control chromosome pairing completely. Evidence for genome homogenization in oilseed rape is presented and its implications on genetic mapping in amphidiploid species is discussed. The level of polymorphism in the A genome was higher than that in the C genome and this might be a general property of oilseed rape crosses.

Analysis of B-Genome Chromosome Introgression in Interspecific Hybrids of Brassica napus × B. carinata

“…Genomic DNA extractions, Southern hybridization, and microsatellite analysis: Genomic DNA extractions and Southern hybridizations, confirming the hybrid genotype of KCN-10, were carried out as described in Sharpe et al (1995). Microsatellite primer pairs, derived from B. nigra, B. juncea, B. rapa, and B. napus, with defined loci in the Brassica A, C, and B genomes were developed by Agriculture and Agri-Food Canada (AAFC), Saskatoon Research Station (http:/ /www.agr.…”

“…The universally agreed nomenclature system as introduced at www.brassica.info is adopted. Using the AAFC reference maps (based on two B. napus and one B. juncea reference mapping populations) Sharpe et al 1995;Lagercrantz and Lydiate 1996;Axelsson et al 2000), markers were selected that mapped at regular intervals along each B and C genome chromosome and that ideally amplified only one or two loci. The SSR markers were evaluated to compare allele sizes in the parents of KCN-10 and in the experimental population to those characterized in the AAFC reference populations and appropriate representative B. nigra (BB), B. oleracea (CC), and B. rapa (AA) lines.…”

Repeated Polyploidy Drove Different Levels of Crossover Suppression between Homoeologous Chromosomes inBrassica napusAllohaploids

“…Natural euploid B. napus displays predominantly 19 bivalents at Metaphase I (MI) and an almost strict disomic inheritance; this shows that the vast majority of COs are formed between homologous chromosomes. Evidence for rare homoeologous exchanges was obtained in several B. napus cultivars Sharpe et al, 1995;Lombard and Delourme, 2001;Osborn et al, 2003;Piquemal et al, 2005;Udall et al, 2005;Howell et al, 2008), but their frequency remains very low compared with the rate in resynthesized B. napus Sharpe et al, 1995;Udall et al, 2005;Lukens et al, 2006;Gaeta et al, 2007;Szadkowski et al, 2010). Contrary to wheat, comparisons of meiosis among B. napus allohaploid plants, which carry one copy of each of the 10 A and 9 C B. napus chromosomes (AC), showed that allohaploids produced from some varieties displayed only a few univalents (i.e., chromosomes that fail to form a CO), whereas those produced from other varieties displayed mostly univalents (Olsson and Hagberg, 1955;Renard and Dosba, 1980;Attia and Rö bbelen, 1986;Jenczewski et al, 2003).…”

Physical mapping of DNA repetitive sequences to mitotic and meiotic chromosomes of Brassica oleracea var. alboglabra by fluorescence in situ hybridization

“…This is of particular importance in the case of Brassica species, where a plethora of independent numbering systems has developed for both chromosomes and linkage groups. We will adopt the nomenclatural framework of Sharpe et al (1995) and Parkin et al (1995), which provides a standard set of designations for both the linkage groups of B. napus (N1-N19) and those of the component B. rapa and B. oleracea genomes.…”