A new method for producing allohexaploid Brassica through unreduced gametes

Mason, Annaliese S.; Yan, Guijun; Cowling, Wallace; Nelson, Matthew N.

doi:10.1007/s10681-011-0537-4

Cited by 32 publications

(36 citation statements)

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“…In our study, both test-crossing and microspore culture yielded .50% unreduced gamete-derived progeny using a number of different interspecific hybrid genotypes. It is interesting to note that test crossing of a single genotype of B. juncea 3 B. napus interspecific hybrid to two genotypes of B. carinata in a previous study yielded only reduced gamete-derived individuals (Mason et al 2012). In this study, the same hybrid genotype of B. juncea 3 B. napus was successfully used to generate 87% unreduced gamete-derived progeny through microspore culture (Table S1, A_MD_03).…”

Section: Discussionmentioning

confidence: 62%

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Centromere Locations inBrassicaA and C Genomes Revealed Through Half-Tetrad Analysis

et al. 2015

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Locating centromeres on genome sequences can be challenging. The high density of repetitive elements in these regions makes sequence assembly problematic, especially when using short-read sequencing technologies. It can also be difficult to distinguish between active and recently extinct centromeres through sequence analysis. An effective solution is to identify genetically active centromeres (functional in meiosis) by half-tetrad analysis. This genetic approach involves detecting heterozygosity along chromosomes in segregating populations derived from gametes (half-tetrads). Unreduced gametes produced by first division restitution mechanisms comprise complete sets of nonsister chromatids. Along these chromatids, heterozygosity is maximal at the centromeres, and homologous recombination events result in homozygosity toward the telomeres. We genotyped populations of half-tetrad-derived individuals (from Brassica interspecific hybrids) using a high-density array of physically anchored SNP markers (Illumina Brassica 60K Infinium array). Mapping the distribution of heterozygosity in these half-tetrad individuals allowed the genetic mapping of all 19 centromeres of the Brassica A and C genomes to the reference Brassica napus genome. Gene and transposable element density across the B. napus genome were also assessed and corresponded well to previously reported genetic map positions. Known centromerespecific sequences were located in the reference genome, but mostly matched unanchored sequences, suggesting that the core centromeric regions may not yet be assembled into the pseudochromosomes of the reference genome. The increasing availability of genetic markers physically anchored to reference genomes greatly simplifies the genetic and physical mapping of centromeres using half-tetrad analysis. We discuss possible applications of this approach, including in species where half-tetrads are currently difficult to isolate.

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Section: Discussionmentioning

confidence: 62%

“…Crossing was carried out according to methods detailed in Mason et al (2012), using the B. napus 3 B. carinata hybrid as the female parent in the cross.…”

Section: Experimental Materialsmentioning

confidence: 99%

Centromere Locations inBrassicaA and C Genomes Revealed Through Half-Tetrad Analysis

et al. 2015

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“…Crossing to generate the allohexaploid hybrid plant (hereafter referred to as "A1"; previously N1C1.J1-1) and preliminary cytological and molecular marker characterization of this plant are detailed in Mason et al (2012) and further details are provided in Figure 1. The source of cytoplasm in A1 was B. napus, with B. carinata and B. juncea used as paternal parents in the formation of A1.…”

Section: Generation and Growth Of Plant Materials And Experimental Popmentioning

confidence: 99%

“…Somewhat increased genomic stability in allohexaploids derived from genotypes of B. rapa 3 B. carinata crosses has recently been demonstrated after several successive generations of selfing and selection for 2n = 54 chromosome complements . Mason et al (2012) mimicked a natural evolutionary pathway for polyploid formation in Brassica by using unreduced gametes to produce an allohexaploid plant. B. napus and B. carinata were crossed in the first generation to create a hybrid with karyotype CCAB (Figure 1).…”

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confidence: 99%

“…B. napus and B. carinata were crossed in the first generation to create a hybrid with karyotype CCAB (Figure 1). An unreduced gamete from this hybrid combined with a reduced gamete from B. juncea (n = AB) to form a near-hexaploid (AABBCC) plant with 2n = 49 chromosomes, 5 short of the full allohexaploid complement (Mason et al 2012) (Figure 1). Low-resolution molecular karyotyping using microsatellite markers indicated that the missing chromosomes were all monosomic deletions [i.e., one copy of each of five different homologous chromosomes was retained in the allohexaploid plant (Mason et al 2012)].…”

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confidence: 99%

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The Fate of Chromosomes and Alleles in an AllohexaploidBrassicaPopulation

et al. 2014

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Production of allohexaploid Brassica (2n = AABBCC) is a promising goal for plant breeders due to the potential for hybrid heterosis and useful allelic contributions from all three of the Brassica genomes present in the cultivated diploid (2n = AA, 2n = BB, 2n = CC) and allotetraploid (2n = AABB, 2n = AACC, and 2n = BBCC) crop species (canola, cabbages, mustards). We used highthroughput SNP molecular marker assays, flow cytometry, and fluorescent in situ hybridization (FISH) to characterize a population of putative allohexaploids derived from self-pollination of a hybrid from the novel cross (B. napus 3 B. carinata) 3 B. juncea to investigate whether fertile, stable allohexaploid Brassica can be produced. Allelic segregation in the A and C genomes generally followed Mendelian expectations for an F 2 population, with minimal nonhomologous chromosome pairing. However, we detected no strong selection for complete 2n = AABBCC chromosome complements, with weak correlations between DNA content and fertility (r 2 = 0.11) and no correlation between missing chromosomes or chromosome segments and fertility. Investigation of next-generation progeny resulting from one highly fertile F 2 plant using FISH revealed general maintenance of high chromosome numbers but severe distortions in karyotype, as evidenced by recombinant chromosomes and putative loss/duplication of A-and C-genome chromosome pairs. Our results show promise for the development of meiotically stable allohexaploid lines, but highlight the necessity of selection for 2n = AABBCC karyotypes.T HE Brassica genus contains the largest number of cultivated crop species of any plant genus (Dixon 2007). Six major crop species are B. rapa (Chinese cabbage, turnip), B. oleracea (cabbage, cauliflower, broccoli), B. nigra (black mustard), B. napus (canola, rapeseed), B. juncea (Indian mustard, leaf mustard), and B. carinata (Ethiopian mustard). These six species share a unique genomic relationship: progenitor diploid species B. rapa (2n = AA), B. oleracea (2n = CC), and B. nigra (2n = BB) gave rise to the allotetraploid species B. juncea (2n = AABB), B. napus (2n = AACC), and B. carinata (2n = BBCC) through pairwise crosses (Morinaga 1934;U 1935). However, despite the fact that each pair of genomes coexists in an allotetraploid species, no naturally occurring allohexaploid species (2n = AABBCC) exists. In general, interspecific hybridization and polyploidy in plants are potent evolutionary mechanisms, allowing formation of new species with adaptation to a wider range of climatic conditions and greater "hybrid vigor" than their progenitor species (Otto and Whitton 2000;Leitch and Leitch 2008). Hence, production of an artificial allohexaploid in the agriculturally important Brassica genus could potentially give rise to new crop types with greater intersubgenomic heterosis ) and tolerance of a wider range of environmental conditions than preexisting Brassica crops (Chen et al. 2011).

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Challenges of Genotyping Polyploid Species

Mason

2014

Methods in Molecular Biology

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Most plant species are known to be either ancient or recent polyploids, containing more than one genome as a result of past interspecific hybridization events (allopolyploidy) and/or genome doubling (autopolyploidy). Genotyping in polyploid species offers a set of unique challenges. Most molecular marker methodologies are made more complex by polyploidy, as multilocus alleles are generally produced when a single locus is targeted. Genotyping by sequencing is also more challenging in polyploids, with problematic assemblies of duplicated regions and difficulties in distinguishing between inter- and intragenomic polymorphisms. Strategies for identifying and overcoming the challenges of polyploidy in plant genotyping are proposed.

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A new method for producing allohexaploid Brassica through unreduced gametes

Cited by 32 publications

References 34 publications

Centromere Locations inBrassicaA and C Genomes Revealed Through Half-Tetrad Analysis

Centromere Locations inBrassicaA and C Genomes Revealed Through Half-Tetrad Analysis

The Fate of Chromosomes and Alleles in an AllohexaploidBrassicaPopulation

Challenges of Genotyping Polyploid Species

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