Polyploid formation pathways have an impact on genetic rearrangements in resynthesized Brassica napus

Abstract

Summary• Polyploids can be produced by the union of unreduced gametes or through somatic doubling of F 1 interspecific hybrids. The first route is suspected to produce allopolyploid species under natural conditions, whereas experimental data have only been thoroughly gathered for the latter.• We analyzed the meiotic behavior of an F 1 interspecific hybrid (by crossing Brassica oleracea and B. rapa, progenitors of B. napus) and the extent to which recombined homoeologous chromosomes were transmitted to its progeny. These results were then compared with results obtained for a plant generated by somatic doubling of this F 1 hybrid (CD.S 0 ) and an amphidiploid (UG.S 0 ) formed via a pathway involving unreduced gametes; we studied the impact of this method of polyploid formation on subsequent generations.• This study revealed that meiosis of the F 1 interspecific hybrid generated more gametes with recombined chromosomes than did meiosis of the plant produced by somatic doubling, although the size of these translocations was smaller. In the progeny of the UG.S 0 plant, there was an unexpected increase in the frequency at which the C1 chromosome was replaced by the A1 chromosome.• We conclude that polyploid formation pathways differ in their genetic outcome. Our study opens up perspectives for the understanding of polyploid origins.

Cytoplasmic and Genomic Effects on Meiotic Pairing in Brassica Hybrids and Allotetraploids from Pair Crosses of Three Cultivated Diploids

“…The genetic changes caused by homeologous chromosome rearrangement were found to be common in newly resynthesized B. napus allotetraploids (Gaeta et al 2007;Szadkowski et al 2010Szadkowski et al , 2011. In the very first meiosis of synthetic B. napus, the frequent occurrence of A-C bivalents and/or multivalents and univalents was detected, which resulted in the production of gametes with unbalanced chromosomal composition and/or carrying chromosomal rearrangements (Szadkowski et al 2010).…”

“…This complex of diploids and allopolyploids is now considered as a model system for studying polyploidization in crop species (Lukens et al 2006;Pires et al 2006). Synthetic Brassica, especially B. napus, has become one of the most widely used models to study the genetic and epigenetic alterations caused by meiosis-driven genome reshuffling in allopolyploids (Gaeta et al 2007;Nicolas et al 2007Nicolas et al , 2009Szadkowski et al 2010Szadkowski et al , 2011Xiong et al 2011) since the seminal work of Song et al (1995).…”

Extraction of the Constituent Subgenomes of the Natural Allopolyploid Rapeseed (Brassica napus L.)

“…The cytological process in mostly studied allohexaploid wheat was realized through two independent but complementary systems: the genetic control of pairing (Ph1 gene) and the physical divergence of the homeologous chromosomes . Owing to the close relatedness between A and C subgenomes in B. napus, homeologous pairings and exchanges were frequently detected in synthetic and natural B. napus (Nicolas et al 2007;Szadkowski et al 2010Szadkowski et al , 2011Cui et al 2012;Chalhoub et al 2014). Specially, whole-chromosome aneuploidy and structural alterations occurred in its progenies of several generations and were biased to those chromosomes with extensive homeology (A1/C1 and A2/C2) , likely resulting from their nondiploidized meiotic pairing (Cui et al 2012).…”

Revisiting the Dioecy-Polyploidy Association: Alternate Pathways and Research Opportunities

“…The extent of rearrangement may be associated with the pathway by which the polyploid was formed (i.e. via somatic doubling alone or in conjunction with hybridization), the genetic distance between the progenitors or the specific parental genotypes involved [Adams et al, 2003;Szadkowski et al, 2011].…”