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Microspore culture reveals complex meiotic behaviour in a trigenomic Brassica hybrid.

Mason AS, Takahira J, Atri C, Samans B, Hayward A, Cowling WA, Batley J, Nelson MN - BMC Plant Biol. (2015)

Bottom Line: Presence of chromosome A6 was positively correlated with self-pollinated seed set and pollen viability in the MD population.Many MD progeny were unable to produce self-pollinated seed (76 %) or viable pollen (53 %), although one MD plant produced 198 self-pollinated seeds.SNP allele copy number analysis revealed the occurrence not only of homoeologous duplication/deletion events but also other cryptic duplications and deletions that may have been the result of mitotic instability.

View Article: PubMed Central - PubMed

Affiliation: School of Agriculture and Food Sciences, The University of Queensland, Brisbane, 4072, Australia. annaliese.mason@agrar.uni-giessen.de.

ABSTRACT

Background: Development of synthetic allohexaploid Brassica (2n = AABBCC) would be beneficial for agriculture, as allelic contributions from three genomes could increase hybrid vigour and broaden adaptation. Microspore culture of a near-allohexaploid hybrid derived from the cross (B. napus × B. carinata) × B. juncea was undertaken in order to assess the frequency and distribution of homologous and homoeologous crossovers in this trigenomic hybrid. SNP and SSR molecular markers were used to detect inheritance of A, B and C genome alleles in microspore-derived (MD) progeny. SNP allele copy number was also assessed. The MD progeny were also compared to progeny derived by self-pollination and open-pollination for fertility (estimated by self-pollinated seed set and pollen viability) and DNA ploidy (measured by flow cytometry).

Results: In the trigenomic hybrid, homologous chromosome pairs A(j)-A(n), B(j)-B(c) and C(n)-C(c) had similar meiotic crossover frequencies and segregation to that previously observed in established Brassica species, as demonstrated by marker haplotype analysis of the MD population. Homoeologous pairing between chromosomes A1-C1, A2-C2 and A7-C6 was detected at frequencies of 12-18 %, with other homoeologous chromosome regions associating from 8 % (A3-C3) to 0-1 % (A8-C8, A8-C9) of the time. Copy number analysis revealed eight instances of additional chromosomes and 20 instances of chromosomes present in one copy in somatically doubled MD progeny. Presence of chromosome A6 was positively correlated with self-pollinated seed set and pollen viability in the MD population. Many MD progeny were unable to produce self-pollinated seed (76 %) or viable pollen (53 %), although one MD plant produced 198 self-pollinated seeds. Average fertility was significantly lower in progeny obtained by microspore culture than progeny obtained by self-pollination or open-pollination, after excluding MD progeny which had not undergone chromosome doubling.

Conclusions: Based on SNP data analysis of the microspore-derived progeny, crossover frequency per chromosome in the allohexaploid hybrid was found to be similar to that in established Brassica species, suggesting that the higher chromosome number did not significantly disrupt cellular regulation of meiosis. SNP allele copy number analysis revealed the occurrence not only of homoeologous duplication/deletion events but also other cryptic duplications and deletions that may have been the result of mitotic instability. Microspore culture simplified the assessment of chromosome behaviour in the allohexaploid hybrid but yielded progeny with lower fertility and a greater range of ploidy levels compared to progeny obtained by self- or open-pollination.

No MeSH data available.


Related in: MedlinePlus

Allele segregation indicative of pairing between homologous (a) A-genome chromosomes (Aj–An), (b) B-genome chromosomes (Bj–Bc) and (c) C-genome chromosomes (Cn–Cc) in a near-allohexaploid hybrid. Allele segregation was assessed in a population of 71 progeny derived from microspores of a 2n = AjAnBjBcCnCc hybrid. Only non-redundant SNP alleles are presented, arranged sequentially according to their genetic location (not drawn to scale). The Bonferroni multiple testing p-value correction for p < 0.05 significance is p < 0.000000050 in this analysis
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Fig4: Allele segregation indicative of pairing between homologous (a) A-genome chromosomes (Aj–An), (b) B-genome chromosomes (Bj–Bc) and (c) C-genome chromosomes (Cn–Cc) in a near-allohexaploid hybrid. Allele segregation was assessed in a population of 71 progeny derived from microspores of a 2n = AjAnBjBcCnCc hybrid. Only non-redundant SNP alleles are presented, arranged sequentially according to their genetic location (not drawn to scale). The Bonferroni multiple testing p-value correction for p < 0.05 significance is p < 0.000000050 in this analysis

Mentions: The regularity of meiotic interactions between homologous chromosomes in the near-allohexaploid hybrid was assessed by detecting associations between all pairs of alleles segregating in the MD population, following the novel method described in [27]. All Aj/An alleles for which a homologous chromosome pair was present (i.e., excluding Aj2, Aj6 and Aj9; Fig. 2) segregated with high fidelity in the MD population, as evidenced by the strong diagonal in the allele association plot shown in Fig. 4a. Exceptions were the bottom third of chromosome A10 and an interstitial part of chromosome A7 (Fig. 4a). In the B genome, all Bj and Bc alleles for which a homologous chromosome pair was present (i.e., excluding Bj3 and Bj7) segregated with high fidelity (Fig. 4b). All Cn/Cc alleles showed regular segregation and putative homologous pairing as assessed by allele transmission to the MD population (Fig. 4c), except for the bottom ends of C6 and C4.Fig. 4


Microspore culture reveals complex meiotic behaviour in a trigenomic Brassica hybrid.

Mason AS, Takahira J, Atri C, Samans B, Hayward A, Cowling WA, Batley J, Nelson MN - BMC Plant Biol. (2015)

Allele segregation indicative of pairing between homologous (a) A-genome chromosomes (Aj–An), (b) B-genome chromosomes (Bj–Bc) and (c) C-genome chromosomes (Cn–Cc) in a near-allohexaploid hybrid. Allele segregation was assessed in a population of 71 progeny derived from microspores of a 2n = AjAnBjBcCnCc hybrid. Only non-redundant SNP alleles are presented, arranged sequentially according to their genetic location (not drawn to scale). The Bonferroni multiple testing p-value correction for p < 0.05 significance is p < 0.000000050 in this analysis
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4493989&req=5

Fig4: Allele segregation indicative of pairing between homologous (a) A-genome chromosomes (Aj–An), (b) B-genome chromosomes (Bj–Bc) and (c) C-genome chromosomes (Cn–Cc) in a near-allohexaploid hybrid. Allele segregation was assessed in a population of 71 progeny derived from microspores of a 2n = AjAnBjBcCnCc hybrid. Only non-redundant SNP alleles are presented, arranged sequentially according to their genetic location (not drawn to scale). The Bonferroni multiple testing p-value correction for p < 0.05 significance is p < 0.000000050 in this analysis
Mentions: The regularity of meiotic interactions between homologous chromosomes in the near-allohexaploid hybrid was assessed by detecting associations between all pairs of alleles segregating in the MD population, following the novel method described in [27]. All Aj/An alleles for which a homologous chromosome pair was present (i.e., excluding Aj2, Aj6 and Aj9; Fig. 2) segregated with high fidelity in the MD population, as evidenced by the strong diagonal in the allele association plot shown in Fig. 4a. Exceptions were the bottom third of chromosome A10 and an interstitial part of chromosome A7 (Fig. 4a). In the B genome, all Bj and Bc alleles for which a homologous chromosome pair was present (i.e., excluding Bj3 and Bj7) segregated with high fidelity (Fig. 4b). All Cn/Cc alleles showed regular segregation and putative homologous pairing as assessed by allele transmission to the MD population (Fig. 4c), except for the bottom ends of C6 and C4.Fig. 4

Bottom Line: Presence of chromosome A6 was positively correlated with self-pollinated seed set and pollen viability in the MD population.Many MD progeny were unable to produce self-pollinated seed (76 %) or viable pollen (53 %), although one MD plant produced 198 self-pollinated seeds.SNP allele copy number analysis revealed the occurrence not only of homoeologous duplication/deletion events but also other cryptic duplications and deletions that may have been the result of mitotic instability.

View Article: PubMed Central - PubMed

Affiliation: School of Agriculture and Food Sciences, The University of Queensland, Brisbane, 4072, Australia. annaliese.mason@agrar.uni-giessen.de.

ABSTRACT

Background: Development of synthetic allohexaploid Brassica (2n = AABBCC) would be beneficial for agriculture, as allelic contributions from three genomes could increase hybrid vigour and broaden adaptation. Microspore culture of a near-allohexaploid hybrid derived from the cross (B. napus × B. carinata) × B. juncea was undertaken in order to assess the frequency and distribution of homologous and homoeologous crossovers in this trigenomic hybrid. SNP and SSR molecular markers were used to detect inheritance of A, B and C genome alleles in microspore-derived (MD) progeny. SNP allele copy number was also assessed. The MD progeny were also compared to progeny derived by self-pollination and open-pollination for fertility (estimated by self-pollinated seed set and pollen viability) and DNA ploidy (measured by flow cytometry).

Results: In the trigenomic hybrid, homologous chromosome pairs A(j)-A(n), B(j)-B(c) and C(n)-C(c) had similar meiotic crossover frequencies and segregation to that previously observed in established Brassica species, as demonstrated by marker haplotype analysis of the MD population. Homoeologous pairing between chromosomes A1-C1, A2-C2 and A7-C6 was detected at frequencies of 12-18 %, with other homoeologous chromosome regions associating from 8 % (A3-C3) to 0-1 % (A8-C8, A8-C9) of the time. Copy number analysis revealed eight instances of additional chromosomes and 20 instances of chromosomes present in one copy in somatically doubled MD progeny. Presence of chromosome A6 was positively correlated with self-pollinated seed set and pollen viability in the MD population. Many MD progeny were unable to produce self-pollinated seed (76 %) or viable pollen (53 %), although one MD plant produced 198 self-pollinated seeds. Average fertility was significantly lower in progeny obtained by microspore culture than progeny obtained by self-pollination or open-pollination, after excluding MD progeny which had not undergone chromosome doubling.

Conclusions: Based on SNP data analysis of the microspore-derived progeny, crossover frequency per chromosome in the allohexaploid hybrid was found to be similar to that in established Brassica species, suggesting that the higher chromosome number did not significantly disrupt cellular regulation of meiosis. SNP allele copy number analysis revealed the occurrence not only of homoeologous duplication/deletion events but also other cryptic duplications and deletions that may have been the result of mitotic instability. Microspore culture simplified the assessment of chromosome behaviour in the allohexaploid hybrid but yielded progeny with lower fertility and a greater range of ploidy levels compared to progeny obtained by self- or open-pollination.

No MeSH data available.


Related in: MedlinePlus