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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

Relative chromosome copy number variation within each individual in a microspore-derived population resulting from a trigenomic Brassica hybrid. Asterisks indicate chromosomes with only one copy in the parent hybrid. One missing chromosome was only assessed in somatically-doubled “2n” progeny, and extra chromosome refers to either two copies in an “n” progeny, or three or four copies in a “2n” progeny
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Fig3: Relative chromosome copy number variation within each individual in a microspore-derived population resulting from a trigenomic Brassica hybrid. Asterisks indicate chromosomes with only one copy in the parent hybrid. One missing chromosome was only assessed in somatically-doubled “2n” progeny, and extra chromosome refers to either two copies in an “n” progeny, or three or four copies in a “2n” progeny

Mentions: Standard SNP marker genotyping does not capture the full extent of homoeologous chromosome interactions, which can result in changes in allele copy numbers. Therefore, we conducted SNP marker allele copy number analysis to detect the deviations from regular chromosome transmission in the MD progeny. Deviations from expected copy numbers were indeed observed, including 8 instances of anomalous extra chromosomes and 20 instances of chromosomes present in only a single copy in “2n” progeny (Fig. 3). Duplication/deletion events involving partial chromosomes were also assessed. Twice as many deletion events (36) were observed in the population compared to duplication events (18), excluding the pre-existing duplication on chromosome A10 (25).Fig. 3


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)

Relative chromosome copy number variation within each individual in a microspore-derived population resulting from a trigenomic Brassica hybrid. Asterisks indicate chromosomes with only one copy in the parent hybrid. One missing chromosome was only assessed in somatically-doubled “2n” progeny, and extra chromosome refers to either two copies in an “n” progeny, or three or four copies in a “2n” progeny
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig3: Relative chromosome copy number variation within each individual in a microspore-derived population resulting from a trigenomic Brassica hybrid. Asterisks indicate chromosomes with only one copy in the parent hybrid. One missing chromosome was only assessed in somatically-doubled “2n” progeny, and extra chromosome refers to either two copies in an “n” progeny, or three or four copies in a “2n” progeny
Mentions: Standard SNP marker genotyping does not capture the full extent of homoeologous chromosome interactions, which can result in changes in allele copy numbers. Therefore, we conducted SNP marker allele copy number analysis to detect the deviations from regular chromosome transmission in the MD progeny. Deviations from expected copy numbers were indeed observed, including 8 instances of anomalous extra chromosomes and 20 instances of chromosomes present in only a single copy in “2n” progeny (Fig. 3). Duplication/deletion events involving partial chromosomes were also assessed. Twice as many deletion events (36) were observed in the population compared to duplication events (18), excluding the pre-existing duplication on chromosome A10 (25).Fig. 3

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