Synaptonemal complex formation in two allohexaploid Festuca species and a pentaploid hybrid

Thomas, Hugh; Thomas, B. J.

doi:10.1038/hdy.1993.140

Cited by 16 publications

(6 citation statements)

References 18 publications

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“…Among allopolyploid Aegilops species, regardless the degree of divergence between homoeologous genomes, the control of the diploid-like meiosis operates by means of restriction of synapsis to homologous chromosomes and suppression of chiasma formation in the infrequent homoeologous associations [ 199 ]. A similar system controlling restriction of chromosome synapsis initiation to homologous chromosomes has also been reported in allopolyploid species of Avena [ 200 ], Festuca [ 201 ], and wild forms of T. turgidum and T. timopheevii [ 202 ]. Surprisingly, the strictly disomic inheritance displayed by the cultivated wheat T. timopheevii is achieved though synaptonemal complex (SC) multivalents are relatively frequent during prophase I [ 203 ].…”

Section: Cytological Diploidization Of Allopolyploidsmentioning

confidence: 62%

Genomic and Meiotic Changes Accompanying Polyploidization

Blasio

Prieto

Pradillo

et al. 2022

Plants

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Hybridization and polyploidy have been considered as significant evolutionary forces in adaptation and speciation, especially among plants. Interspecific gene flow generates novel genetic variants adaptable to different environments, but it is also a gene introgression mechanism in crops to increase their agronomical yield. An estimate of 9% of interspecific hybridization has been reported although the frequency varies among taxa. Homoploid hybrid speciation is rare compared to allopolyploidy. Chromosome doubling after hybridization is the result of cellular defects produced mainly during meiosis. Unreduced gametes, which are formed at an average frequency of 2.52% across species, are the result of altered spindle organization or orientation, disturbed kinetochore functioning, abnormal cytokinesis, or loss of any meiotic division. Meiotic changes and their genetic basis, leading to the cytological diploidization of allopolyploids, are just beginning to be understood especially in wheat. However, the nature and mode of action of homoeologous recombination suppressor genes are poorly understood in other allopolyploids. The merger of two independent genomes causes a deep modification of their architecture, gene expression, and molecular interactions leading to the phenotype. We provide an overview of genomic changes and transcriptomic modifications that particularly occur at the early stages of allopolyploid formation.

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Section: Cytological Diploidization Of Allopolyploidsmentioning

confidence: 62%

Genomic and Meiotic Changes Accompanying Polyploidization

Blasio

Prieto

Pradillo

et al. 2022

Plants

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“…In that case, B. napus would be like wheat, Aegilops, and Festuca polyploids, in which varying numbers of homologous and homoeologous chromosomes are partially synapsed during prophase I (Hobolth, 1981;Thomas and Thomas, 1993;Cuñado et al, 1996). Given that, in plants, the synaptonemal complex does not form when strand invasion is impaired (Osman et al, 2011), the presence of homoeologous synaptic associations most likely indicates that strand exchanges are initiated between homoeologs in B. napus euploids.…”

Section: Discussion Early Homoeologous Chromosome Sorting In B Napusmentioning

confidence: 99%

Homoeologous Chromosome Sorting and Progression of Meiotic Recombination inBrassica napus: Ploidy Does Matter!

et al. 2014

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Meiotic recombination is the fundamental process that produces balanced gametes and generates diversity within species. For successful meiosis, crossovers must form between homologous chromosomes. This condition is more difficult to fulfill in allopolyploid species, which have more than two sets of related chromosomes (homoeologs). Here, we investigated the formation, progression, and completion of several key hallmarks of meiosis in Brassica napus (AACC), a young polyphyletic allotetraploid crop species with closely related homoeologous chromosomes. Altogether, our results demonstrate a precocious and efficient sorting of homologous versus homoeologous chromosomes during early prophase I in two representative B. napus accessions that otherwise show a genotypic difference in the progression of homologous recombination. More strikingly, our detailed comparison of meiosis in near isogenic allohaploid and euploid plants showed that the mechanism(s) promoting efficient chromosome sorting in euploids is adjusted to promote crossover formation between homoeologs in allohaploids. This suggests that, in contrast to other polyploid species, chromosome sorting is context dependent in B. napus.

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“…A restriction of chromosome synapsis initiation to homologous chromosomes has also been reported in allopolyploid species of Avena (Jones et al, 1989), Festuca (Thomas and Thomas, 1993), and wild forms of Triticum turgidum and T. timopheevii (Martínez et al, 2001a). Surprisingly, the strictly disomic inheritance displayed by the cultivated wheats Triticum timopheevii, T. turgidum, and T. aestivum is achieved despite their showing a relatively high frequency of SC multivalents at prophase I (Holm, 1986;Martínez et al, 1996Martínez et al, , 2001b.…”

Section: Discussionmentioning

confidence: 96%

Understanding the cytological diploidization mechanism of polyploid wild wheats

Cuñado¹,

Blázquez²,

Melchor³

et al. 2005

Cytogenet Genome Res

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The allohexaploid Aegilops species (2n = 6x = 42), Ae. neglecta 6x (UUX^tX^tNN), Ae. juvenalis (D^cD^cX^cX^cUU), and Ae. vavilovii (D^cD^cX^cX^cS^sS^s) regularly form bivalents at metaphase I. However, in Ae. crassa 6x (D^cD^cX^cX^cDD) 0.27 quadrivalents per cell were observed probably as a consequence of the partial homology displayed by the D and D^c genomes. Likewise, the synthetic amphiploid Ae. ventricosa-Secale cereale (DDNNRR) is fertile and displays a diploid-like behavior at metaphase I, despite its recent origin. The pattern of synapsis at late zygotene and pachytene in the natural and artificial allohexaploids was analyzed by whole-mount surface-spreading of synaptonemal complexes under an electron microscope. It revealed that chromosomes were mostly associated as bivalents in all cases, the mean of multivalents per nucleus ranging from 0.17 (Ae. neglecta 6x) to 1.03 (Ae. crassa 6x) in the natural species and 1.05 in the Ae. ventricosa-S. cereale amphiploid. It can be concluded that the mechanism controlling bivalent formation in these species and also in the synthetic amphiploid acts mainly at zygotene by restricting synapsis to homologous chromosomes, but also acts at pachytene by preventing chiasma formation in the homoeologous associations. These observations are discussed in relation to the origin and evolution of the mechanism of diploidization in the allopolyploid species of the Poaceae family.

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Synaptonemal complex formation in two allohexaploid Festuca species and a pentaploid hybrid

Cited by 16 publications

References 18 publications

Genomic and Meiotic Changes Accompanying Polyploidization

Genomic and Meiotic Changes Accompanying Polyploidization

Homoeologous Chromosome Sorting and Progression of Meiotic Recombination inBrassica napus: Ploidy Does Matter!

Understanding the cytological diploidization mechanism of polyploid wild wheats

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