Meiotic pairing in haploids and amphidiploids of spontaneous versus synthetic origin in rape, Brassica napus L.

Abstract

ATTIA, T., and G. ROBBELEN. 1986. Meiotic pairing in haploids and amphidiploids of spontaneous versus synthetic origin in rape, Brassica napus L. Can. J . Genet. Cytol. 28: 330-334. Newly resynthesized AC amphihaploids, which were characterized by high meiotic pairing and multivalent formulation, after doubling of their chromosome number showed preferential pairing and bivalent formation in the resynthesized amphidiploid Brassica napus (AACC). However, univalents as well as multivalents were also formed indicating that their chromosome behaviour was not fully diploidized. Stabilization of chromosome pairing in newly resynthesized amphidiploids can be achieved through genetic control or structural modification of the homoeologous chromosomes. A comparison of the meiotic behaviour of spontaneous haploids of natural rapeseed with that of the newly synthesized AC amphihaploids provides some evidence that both processes may be involved in the regulation of chromosome pairing in Brassica.ATTIA, T., et G. ROBBELEN. 1986. Meiotic pairing in haploids and amphidiploids of spontaneous versus synthetic origin in rape, Brassica napus L. Can. J . Genet. Cytol. 28: 330-334. Des amphihaploi'des AC nouvellement resynthktiskes, caractktiskes par un appariement klevk a la mkiose et la formation de multivalents, ont montrk apr6s le doublement de leurs chromosomes un appariement prkfkrentiel et la formation de bivalents chez les amphidiploi'des resynthktiskes de Brassica napus (AACC). Toutefois, des univalents et des multivalents ont aussi kt6 formks, ce qui indique que le comportement des chromosomes n'ktait pas entierement diploi'disk. La stabilisation de l'appariement des chromosomes peut Ctre obtenue soit par le contr6le gknktique, soit par la modification structurale des chromosomes homkologues. Une comparaison entre le comportement mkiotique des haploi'des spontankes naturelles chez le colza et celui des amphidiploi'des AC nouvellement synthktiskes procure une evidence a l'effet que les deux processus peuvent Ctre impliquks dans la rkgulation de l'appariement des chromosomes chez Brassica.

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

“…Although phenotyping other B. napus accessions could provide supplementary information, the dichotomy of meiotic behaviors found here certainly highlights the overall variation present in this species, which contains germplasm of shared recent common ancestry (Prakash and Hinata, 1980;Allender and King, 2010). This observation and the fact that no other meiotic behavior was found in a handful of other accessions (Olsson and Hagberg, 1955;Renard and Dosba, 1980;Attia and Rö bbelen, 1986;Tai and Ikonen, 1988) suggest that most B. napus allohaploids display either a high (MU phenotype) or a low (fu phenotype) number of univalents, with only slight variations within these two canonical phenotypes (Figure 2). These slight variations may reflect either the segregation of genes modifying chiasma frequency or, alternatively, the occurrence of chromosomal changes that differ between accessions (discussed in Udall et al, 2005;Liu et al, 2006).…”

“…We effectively observed natural variation for recombination between homoeologous chromosomes that relied on two clear-cut meiotic phenotypes. Rough estimates of chiasma frequencies indicated that MU allohaploids displayed a range of two to six chiasmata per PMC, whereas the number of chiasmata per PMC varied from 9 to 12 in fu allohaploids (see also Renard and Dosba, 1980;Attia and Rö bbelen, 1986). As already stated in Nicolas et al (2009), this variation does not reflect a difference in the number of chiasmata that are formed on the recombining bivalents, which are strikingly similar between fu and MU allohaploids (;1.4 COs per bivalent on average).…”

“…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). The quantitative trait loci (QTL) determining these phenotypes were mapped in a single population.…”

Mapping PrBn and Other Quantitative Trait Loci Responsible for the Control of Homeologous Chromosome Pairing in Oilseed Rape (Brassica napus L.) Haploids

“…Different authors have proposed that homeologous pairing is genetically regulated in oilseed rape (Attia and Robbelen 1986;Sharpe et al 1995) and its close relatives (Prakash 1974;Hardberg 1976;Eber et al 1994). A major contribution to this debate came from Renard and Dosba (1980) and Attia and Robbelen (1986), who observed that homeologous pairing was commonplace at metaphase I in B. napus haploids (AC; n ¼ 19), and the number of bivalents in pollen mother cells varied with varieties, with highand low-pairing varieties being clearly distinguished. Jenczewski et al (2003) combined a segregation analysis with a maximum-likelihood approach to demonstrate that the distribution of the number of univalents (nonpaired chromosomes) among these haploids was consistent with the segregation of a diallelic major gene, named PrBn for Pairing regulator in B. napus, in a background of polygenic variation.…”

Understanding meiosis and the implications for crop improvement

“…The meiotic behaviour of several allopolyploid plant species has been, and continues to be, studied. These include bread wheat (Riley and Chapman 1958;Sears 1982;Martinez-Perez et al 2001;Griffiths et al 2006;Colas et al 2008;Boden et al 2009), oilseed rape (Brassica napus L.) (Attia and Robbelen 1986;Jenczewski et al 2003;Udall et al 2005;Leflon et al 2006;Liu et al 2006;Nicolas et al 2008Nicolas et al , 2009, oats (Avena sativa L.) (Gauthier and McGinnis 1968;Rajhathy and Thomas 1972), cotton (Gossypium hirsutum L.) (Brown 1954;Reyes-Valdés and Stelly 1995;Ji et al 2007;Vafaie-Tabar and Chandrashekaran 2007) and tobacco (Nicotiana tabacum L.) Berbeć2003, 2007). Of all these plant species, the hexaploid genome of bread wheat has provided some of the most useful information to date.…”