Abstract
Summary Brassica napus (AnAnCnCn) is an important worldwide oilseed crop, but it is a young allotetraploid with a short evolutionary history and limited genetic diversity. To significantly broaden its genetic diversity and create a novel heterotic population for sustainable rapeseed breeding, this study reconstituted the genome of B. napus by replacing it with the subgenomes from 122 accessions of Brassica rapa (ArAr) and 74 accessions of Brassica carinata (BcBcCcCc) and developing a novel gene pool of B. napus through five rounds of extensive recurrent selection. When compared with traditional B. napus using SSR markers and high‐throughput SNP/Indel markers through genotyping by sequencing, the newly developed gene pool and its homozygous progenies exhibited a large genetic distance, rich allelic diversity, new alleles and exotic allelic introgression across all 19 AC chromosomes. In addition to the abundant genomic variation detected in the AC genome, we also detected considerable introgression from the eight chromosomes of the B genome. Extensive trait variation and some genetic improvements were present from the early recurrent selection to later generations. This novel gene pool produced equally rich phenotypic variation and should be valuable for rapeseed genetic improvement. By reconstituting the genome of B. napus by introducing subgenomic variation within and between the related species using intense selection and recombination, the whole genome could be substantially reorganized. These results serve as an example of the manipulation of the genome of a young allopolyploid and provide insights into its rapid genome evolution affected by interspecific and intraspecific crosses.
Highlights
The introgression of genomic regions from related species into a target crop has been used frequently for germplasm innovation, for a single locus and at the whole-genome level (Becker et al, 1995; Dhaliwal et al, 2017; Kuligowska et al, 2016; Mallet, 2005; Multani et al, 2003; Yu et al, 2012; Zamir, 2001; Zhan et al, 2017)
Brassica napus (AnAnCnCn) is an important oilseed crop grown worldwide but is a relatively young species derived from natural interspecific crosses of two diploid progenitors, B. rapa (ArAr) and Brassica oleracea (CoCo), approximately 7.5 thousand years ago; B. napus was only domesticated as an oilseed crop approximately 400 years ago and has a very short evolutionary and domestication history (Chalhoub et al, 2014)
To maintain and create additional novel genetic diversity, this study demonstrated a strategy to reorganize the genome of B. napus by creating a dynamic, novel breeding gene pool of the G3 new-type B. napus with improved traits; these lines were achieved through extensive recombination within and between a Poly-a B. rapa (Ar) subpopulation and Poly-Cc subpopulation with the assistance of a mating system of dominant genic male sterility (DGMS) (Li et al, 1985; Liu et al, 2008) by facilitated intercrossing among different RS lines in each cycle and five rounds of recurrent selection on a range of important traits
Summary
The introgression of genomic regions from related species into a target crop has been used frequently for germplasm innovation, for a single locus and at the whole-genome level (Becker et al, 1995; Dhaliwal et al, 2017; Kuligowska et al, 2016; Mallet, 2005; Multani et al, 2003; Yu et al, 2012; Zamir, 2001; Zhan et al, 2017). To utilize the variation among the different basic genomes and different subgenomes to broaden the genetic diversity of B. napus, many studies have introgressed genomic regions from a single related species and even other genera, such as B. rapa (Qian et al, 2005), B. oleracea (Li et al, 2014; Quazi, 1988), Brassica juncea (Roy, 1984), B. carinata (Navabi et al, 2010, 2011), Brassica maurorum (Chrungu et al, 1999), Sinapis arvensis (Hu et al, 2002) and Isatis indigotica (Kang et al, 2017). Substantial efforts have been extended to resynthesize B. napus by combining the genomes from two or more species, such as crossing B. rapa with B. oleracea (Becker et al, 1995; Hansen and Earle, 1994; Nagaharu, 1935), B. juncea with B. carinata (Chatterjee et al, 2016), and B. carinata with B. rapa (Li et al, 2004, 2006; Xiao et al, 2010)
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