Chromosome instabilities in resynthesized Brassica napus revealed by FISH

Katarzyna Sosnowska,Marta Kasprowicz,Jan Bocianowski,Joanna Majka,Teresa Cegielska-Taras,Maciej Majka,Laurencja Szała,Tomasz Książczyk

doi:10.1007/s13353-020-00557-5

Abstract

Brassica napus is an allopolyploid plant, derived from spontaneous hybridization between Brassica rapa and Brassica oleracea. Intensive breeding has led to a significant reduction in genetic and phenotypic diversity within this species. Newly resynthesized hybrids from progenitor species may restore some diversity in B. napus, but they often are chromosomally and phenotypically unstable. Using fluorescence in situ hybridization, we tested chromosome constitutions in a range of new allopolyploids resynthesized from various parental species. A majority of these allopolyploids were euploid, with the expected chromosome numbers and constitutions, but deviations were also identified. We detected a low level of intergenomic rearrangements in analyzed hybrids and a high level of changes in rDNA loci. Our study revealed a significant effect of maternal cross combination on loss of 35S rDNA loci, especially when B. rapa was the maternal parent. The studied lines were characterized by diversified of pollen viability. In the analyzed hybrids, the erucic acid level in the seed oil ranged from 0 to 43.4% and total glucosinolate content in seeds ranged from 24.3 to 119.2 μmol g−1. Our study shows that cytogenetic analysis of B. napus resynthesized hybrids would be useful in breeding for the selection of lines with important agricultural characters and genetically stable stock seed production.

Highlights

Polyploidy is a common phenomenon in flowering plant evolution, leading to biodiversity and the rapid formation of new species (Wood et al 2009; Madlung 2013)
Our study revealed a significant effect of maternal cross combination on loss of 35S rDNA loci, especially when B. rapa was the maternal parent
Our study shows that cytogenetic analysis of B. napus resynthesized hybrids would be useful in breeding for the selection of lines with important agricultural characters and genetically stable stock seed production

Summary

Introduction

Polyploidy is a common phenomenon in flowering plant evolution, leading to biodiversity and the rapid formation of new species (Wood et al 2009; Madlung 2013). Interspecific hybridization between different species and distinct genomes can cause extensive genetic instability, e.g., genome rearrangements (Song et al 1995; Pontes et al 2004; Udall et al 2005), parental DNA sequence elimination (Han et al 2005), transposon activation, transposoninduced insertional mutagenesis (Kashkush et al 2003; Madlung et al 2005), gene conversion (Kovarik et al 2004, 2005), epigenetic changes (Adams et al 2003; Levy and Feldman 2004; Książczyk et al 2011), and a wide range of further structural or functional genome modifications (Gaeta et al 2007; Szadkowski et al 2010; Zou et al 2010; Pires and Gaeta 2011; Majka et al 2018). Exchanges between homoeologous chromosomes are extensive in this species and have the effect of creating novel allele combinations and phenotypic variation in newly formed B. napus allopolyploids (Osborn et al 2003; Udall et al 2005; Gaeta et al 2007; Ge et al 2009). Fujii and Ohmido (2011) reported that the consequences of aberrant meiosis may result in abnormal chromosome number and structure, which can lead to atypical phenotypes

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