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Reconstituting the genome of a young allopolyploid crop, Brassica napus, with its related species.

ABSTRACT: Brassica napus (Aⁿ Aⁿ Cⁿ Cⁿ ) 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 (A^r A^r ) and 74 accessions of Brassica carinata (B^c B^c C^c C^c ) 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.

SUBMITTER: Hu D

PROVIDER: S-EPMC6523605 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature

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Reconstituting the genome of a young allopolyploid crop, Brassica napus, with its related species.

Hu Dandan D Zhang Wenshan W Zhang Yikai Y Chang Shihao S Chen Lunlin L Chen Yingying Y Shi Yongdi Y Shen Jinxiong J Meng Jinling J Zou Jun J

Plant biotechnology journal 20190107 6

Brassica napus (An An Cn Cn ) 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 (Ar Ar ) and 74 accessi ...[more]

PMID: 30467941

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Project description:BACKGROUND: Single nucleotide polymorphisms (SNPs) are the most common type of genetic variation. Identification of large numbers of SNPs is helpful for genetic diversity analysis, map-based cloning, genome-wide association analyses and marker-assisted breeding. Recently, identifying genome-wide SNPs in allopolyploid Brassica napus (rapeseed, canola) by resequencing many accessions has become feasible, due to the availability of reference genomes of Brassica rapa (2n = AA) and Brassica oleracea (2n = CC), which are the progenitor species of B. napus (2n = AACC). Although many SNPs in B. napus have been released, the objective in the present study was to produce a larger, more informative set of SNPs for large-scale and efficient genotypic screening. Hence, short-read genome sequencing was conducted on ten elite B. napus accessions for SNP discovery. A subset of these SNPs was randomly selected for sequence validation and for genotyping efficiency testing using the Illumina GoldenGate assay. RESULTS: A total of 892,536 bi-allelic SNPs were discovered throughout the B. napus genome. A total of 36,458 putative amino acid variants were located in 13,552 protein-coding genes, which were predicted to have enriched binding and catalytic activity as a result. Using the GoldenGate genotyping platform, 94 of 96 SNPs sampled could effectively distinguish genotypes of 130 lines from two mapping populations, with an average call rate of 92%. CONCLUSIONS: Despite the polyploid nature of B. napus, nearly 900,000 simple SNPs were identified by whole genome resequencing. These SNPs were predicted to be effective in high-throughput genotyping assays (51% polymorphic SNPs, 92% average call rate using the GoldenGate assay, leading to an estimated >450 000 useful SNPs). Hence, the development of a much larger genotyping array of informative SNPs is feasible. SNPs identified in this study to cause non-synonymous amino acid substitutions can also be utilized to directly identify causal genes in association studies.

Project description:BackgroundLong noncoding RNAs (lncRNAs) are transcripts longer than 200 bp that do not encode proteins but nonetheless have been shown to play important roles in various biological processes in plants. Brassica napus is an important seed oil crop worldwide and the target of many genetic improvement activities. To understand better the function of lncRNAs in regulating plant metabolic activities, we carried out a genome-wide lncRNA identification of lncRNAs in Brassica napus with a focus on lncRNAs involved in lipid metabolism. Twenty ribosomal RNA depleted strand specific RNA-seq (ssRNA-seq) datasets were generatred using RNAs isolated from B. napus seeds at four developmental stages. For comparison we also included 30 publically available RNA-seq datasets generated from poly(A) enriched mRNAs isolated from from various Brassica napus tissues in our analysis.ResultsA total of 8905 lncRNA loci were identified, including 7100 long intergenic noncoding RNA (lincRNA) loci and 1805 loci generating long noncoding natural antisense transcript (lncNAT). Many lncRNAs were identified only in the ssRNA-seq and poly(A) RNA-seq dataset, suggesting that B. napus has a large lncRNA repertoire and it is necessary to use libraries prepared from different tissues and developmental stages as well as different library preparation approaches to capture the whole spectrum of lncRNAs. Analysis of coexpression networks revealed that among the regulatory modules are networks containing lncRNAs and protein-coding genes related to oil biosynthesis indicating a possible role of lncRNAs in the control of lipid metabolism. One such example is that several lncRNAs are potential regulators of BnaC08g11970D that encodes oleosin1, a protein found in oil bodies and involved in seed lipid accumulation. We also observed that the expression levels of B. napus lncRNAs is positively correlated with their conservation levels.ConclusionsWe demonstrated that the B. napus genome has a large number of lncRNA and that these lncRNAs are expressed broadly across many developmental times and in different tissue types. We also provide evidence indicating that specific lncRNAs appear to be important regulators of lipid biosynthesis forming regulatory networks with transcripts involved in lipid biosynthesis. We also provide evidence that these lncRNAs are conserved in other species of the Brassicaceae family.

Project description:Auxin response factor (ARF) is a member of the plant-specific B3 DNA binding superfamily. Here, we report the results of a comprehensive analysis of ARF genes in allotetraploid Brassica napus (2n = 38, AACC). Sixty-seven ARF genes were identified in B. napus (BnARFs) and divided into four subfamilies (I-IV). Sixty-one BnARFs were distributed on all chromosomes except C02; the remaining were on Ann and Cnn. The full length of the BnARF proteins was highly conserved especially within each subfamily with all members sharing the N-terminal DNA binding domain (DBD) and the middle region (MR), and most contained the C-terminal dimerization domain (PBI). Twenty-one members had a glutamine-rich MR that may be an activator and the remaining were repressors. Accordingly, the intron patterns are highly conserved in each subfamily or clade, especially in DBD and PBI domains. Several members in subfamily III are potential targets for miR167. Many putative cis-elements involved in phytohormones, light signaling responses, and biotic and abiotic stress were identified in BnARF promoters, implying their possible roles. Most ARF proteins are likely to interact with auxin/indole-3-acetic acid (Aux/IAA) -related proteins, and members from different subfamilies generally shared many common interaction proteins. Whole genome-wide duplication (WGD) by hybridization between Brassica rapa and Brassica oleracea and segmental duplication led to gene expansion. Gene loss following WGD is biased with the An-subgenome retaining more ancestral genes than the Cn-subgenome. BnARFs have wide expression profiles across vegetative and reproductive organs during different developmental stages. No obvious expression bias was observed between An- and Cn-subgenomes. Most synteny-pair genes had similar expression patterns, indicating their functional redundancy. BnARFs were sensitive to exogenous IAA and 6-BA treatments especially subfamily III. The present study provides insights into the distribution, phylogeny, and evolution of ARF gene family.

Project description:BackgroundHigh-density single-nucleotide polymorphism (SNP) genotyping arrays are a powerful tool for genome-wide association studies and can give valuable insight into patterns of population structure and linkage disequilibrium (LD). In this study we used the Brassica 60kSNP Illumina consortium genotyping array to assess the influence of selection and breeding for important agronomic traits on LD and haplotype structure in a diverse panel of 203 Chinese semi-winter rapeseed (Brassica napus) breeding lines.ResultsPopulation structure and principal coordinate analysis, using a subset of the SNPs, revealed diversification into three subpopulations and one mixed population, reflecting targeted introgressions from external gene pools during breeding. Pairwise LD analysis within the A- and C-subgenomes of allopolyploid B. napus revealed that mean LD, at a threshold of r2=0.1, decayed on average around ten times more rapidly in the A-subgenome (0.25-0.30 Mb) than in the C-subgenome (2.00-2.50 Mb). A total of 3,097 conserved haplotype blocks were detected over a total length of 182.49 Mb (15.17% of the genome). The mean size of haplotype blocks was considerably longer in the C-subgenome (102.85 Kb) than in the A-subgenome (33.51 Kb), and extremely large conserved haplotype blocks were found on a number of C-genome chromosomes. Comparative sequence analysis revealed conserved blocks containing homoloeogous quantitative trait loci (QTL) for seed erucic acid and glucosinolate content, two key seed quality traits under strong agronomic selection. Interestingly, C-subgenome QTL were associated with considerably greater conservation of LD than their corresponding A-subgenome homoeologues.ConclusionsThe data we present in this paper provide evidence for strong selection of large chromosome regions associated with important rapeseed seed quality traits conferred by C-subgenome QTL. This implies that an increase in genetic diversity and recombination within the C-genome is particularly important for breeding. The resolution of genome-wide association studies is also expected to vary greatly across different genome regions.

Dataset Information

Reconstituting the genome of a young allopolyploid crop, Brassica napus, with its related species.

Publications

Reconstituting the genome of a young allopolyploid crop, Brassica napus, with its related species.

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