| 1. |
- Bachmann, Jörg A., et al.
(författare)
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Genetic basis and timing of a major mating system shift in Capsella
- 2019
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 224:1, s. 505-517
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Tidskriftsartikel (refereegranskat)abstract
- A crucial step in the transition from outcrossing to self-fertilization is the loss of genetic self-incompatibility (SI). In the Brassicaceae, SI involves the interaction of female and male specificity components, encoded by the genes SRK and SCR at the self-incompatibility locus (S-locus). Theory predicts that S-linked mutations, and especially dominant mutations in SCR, are likely to contribute to loss of SI. However, few studies have investigated the contribution of dominant mutations to loss of SI in wild plant species. Here, we investigate the genetic basis of loss of SI in the self-fertilizing crucifer species Capsella orientalis, by combining genetic mapping, long-read sequencing of complete S-haplotypes, gene expression analyses and controlled crosses. We show that loss of SI in C. orientalis occurred S-locus. We identify a fixed frameshift deletion in the male specificity gene SCR and confirm loss of male SI specificity. We further identify an S-linked small RNA that is predicted to cause dominance of self-compatibility. Our results agree with predictions on the contribution of dominant S-linked mutations to loss of SI, and thus provide new insights into the molecular basis of mating system transitions.
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| 2. |
- Bachmann, Jörg A., et al.
(författare)
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On the origin of the widespread self-compatible allotetraploid Capsella bursa-pastoris (Brassicaceae)
- 2021
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Ingår i: Heredity. - : Springer Science and Business Media LLC. - 0018-067X .- 1365-2540. ; 127, s. 124-134
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Tidskriftsartikel (refereegranskat)abstract
- Polyploidy, or whole-genome duplication, is a common speciation mechanism in plants. An important barrier to polyploid establishment is a lack of compatible mates. Because self-compatibility alleviates this problem, it has long been hypothesized that there should be an association between polyploidy and self-compatibility (SC), but empirical support for this prediction is mixed. Here, we investigate whether the molecular makeup of the Brassicaceae self-incompatibility (SI) system, and specifically dominance relationships among S-haplotypes mediated by small RNAs, could facilitate loss of SI in allopolyploid crucifers. We focus on the allotetraploid species Capsella bursa-pastoris, which formed similar to 300 kya by hybridization and whole-genome duplication involving progenitors from the lineages of Capsella orientalis and Capsella grandiflora. We conduct targeted long-read sequencing to assemble and analyze eight full-length S-locus haplotypes, representing both homeologous subgenomes of C. bursa-pastoris. We further analyze small RNA (sRNA) sequencing data from flower buds to identify candidate dominance modifiers. We find that C. orientalis-derived S-haplotypes of C. bursa-pastoris harbor truncated versions of the male SI specificity gene SCR and express a conserved sRNA-based candidate dominance modifier with a target in the C. grandiflora-derived S-haplotype. These results suggest that pollen-level dominance may have facilitated loss of SI in C. bursa-pastoris. Finally, we demonstrate that spontaneous somatic tetraploidization after a wide cross between C. orientalis and C. grandiflora can result in production of self-compatible tetraploid offspring. We discuss the implications of this finding on the mode of formation of this widespread weed.
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| 3. |
- Dziasek, Katarzyna, et al.
(författare)
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Hybrid seed incompatibility in Capsella is connected to chromatin condensation defects in the endosperm
- 2021
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Ingår i: PLOS Genetics. - : Public Library of Science (PLoS). - 1553-7390 .- 1553-7404. ; 17:2
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Tidskriftsartikel (refereegranskat)abstract
- Hybridization of closely related plant species is frequently connected to endosperm arrest and seed failure, for reasons that remain to be identified. In this study, we investigated the molecular events accompanying seed failure in hybrids of the closely related species pair Capsella rubella and C. grandiflora. Mapping of QTL for the underlying cause of hybrid incompatibility in Capsella identified three QTL that were close to pericentromeric regions. We investigated whether there are specific changes in heterochromatin associated with interspecific hybridizations and found a strong reduction of chromatin condensation in the endosperm, connected with a strong loss of CHG and CHH methylation and random loss of a single chromosome. Consistent with reduced DNA methylation in the hybrid endosperm, we found a disproportionate deregulation of genes located close to pericentromeric regions, suggesting that reduced DNA methylation allows access of transcription factors to targets located in heterochromatic regions. Since the identified QTL were also associated with pericentromeric regions, we propose that relaxation of heterochromatin in response to interspecies hybridization exposes and activates loci leading to hybrid seed failure.
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| 4. |
- Köhler, Claudia, et al.
(författare)
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Evolution and function of epigenetic processes in the endosperm
- 2015
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Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The endosperm is an ephemeral tissue surrounding the embryo that is essential for its development. Aside from the embryo nourishing function, the endosperm serves as a battlefield for epigenetic processes that have been hypothesized to reinforce transposable element silencing in the embryo. Specifically, global DNA demethylation in the central cell may serve to produce small RNAs that migrate to egg cell and embryo to induce de novo DNA methylation. The Polycomb Repressive Complex 2 (PRC2) is particularly targeted to DNA hypomethylated regions, possibly alleviating the negative effects associated with loss of DNA methylation in the endosperm. The functional requirement of the PRC2 in the endosperm can be bypassed by increasing the maternal genome dosage in the endosperm, suggesting a main functional role of the endosperm PRC2 in reducing sexual conflict. We therefore propose that the functional requirement of an endosperm PRC2 was coupled to the evolution of a sexual endosperm and mechanisms enforcing transposon silencing in the embryo. The evolutionary consequences of this scenario for genome expansion will be discussed.
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| 5. |
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| 6. |
- Lafon-Placette, Clément, et al.
(författare)
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Embryo and endosperm, partners in seed development
- 2014
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Ingår i: Current Opinion in Plant Biology. - : Elsevier BV. - 1369-5266 .- 1879-0356. ; 17, s. 64-69
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Forskningsöversikt (refereegranskat)abstract
- Angiosperm seeds are the major source of human calories, generating a pressing need to understand the underlying processes governing seed growth and development. They are composed of the two fertilization products, embryo and endosperm surrounded by the maternally derived seed coat. The successful interaction of all three seed components is a requirement for seeds to complete their development and to produce viable embryos that are competent to establish a new sporophytic generation. Here, we review recent reports investigating signal exchange between embryo and endosperm, focusing in particular on the transport of metabolites and small RNAs between both fertilization products.
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| 7. |
- Lafon-Placette, Clément, et al.
(författare)
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Endosperm-based hybridization barriers explain the pattern of gene flow between Arabidopsis lyrata and Arabidopsis arenosa in Central Europe
- 2017
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 114, s. E1027-E1035
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Tidskriftsartikel (refereegranskat)abstract
- Based on the biological species concept, two species are considered distinct if reproductive barriers prevent gene flow between them. In Central Europe, the diploid species Arabidopsis lyrata and Arabidopsis arenosa are genetically isolated, thus fitting this concept as "good species." Nonetheless, interspecific gene flow involving their tetraploid forms has been described. The reasons for this ploidy-dependent reproductive isolation remain unknown. Here, we show that hybridization between diploid A. lyrata and A. arenosa causes mainly inviable seed formation, revealing a strong postzygotic reproductive barrier separating these two species. Although viability of hybrid seeds was impaired in both directions of hybridization, the cause for seed arrest differed. Hybridization of A. lyrata seed parents with A. arenosa pollen donors resulted in failure of endosperm cellularization, whereas the endosperm of reciprocal hybrids cellularized precociously. Endosperm cellularization failure in both hybridization directions is likely causal for the embryo arrest. Importantly, natural tetraploid A. lyrata was able to form viable hybrid seeds with diploid and tetraploid A. arenosa, associated with the reestablishment of normal endosperm cellularization. Conversely, the defects of hybrid seeds between tetraploid A. arenosa and diploid A. lyrata were aggravated. According to these results, we hypothesize that a tetraploidization event in A. lyrata allowed the production of viable hybrid seeds with A. arenosa, enabling gene flow between the two species.
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| 8. |
- Lafon-Placette, Clément, et al.
(författare)
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Endosperm-based postzygotic hybridization barriers: developmental mechanisms and evolutionary drivers
- 2016
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 25, s. 2620-2629
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Tidskriftsartikel (refereegranskat)abstract
- The endosperm is a nourishing tissue that serves to support embryo growth. Failure of endosperm development will ultimately cause embryo arrest and seed lethality, a phenomenon that is frequently observed upon hybridization of related plant species or species that differ in ploidy. Endosperm-based interspecies or interploidy hybridization barriers depend on the direction of the hybridization, causing nonreciprocal seed defects. This reveals that the parental genomes are not equivalent, implicating parent-of-origin specific genes generating this type of hybridization barrier. Recent work revealed that endosperm-based hybridization barriers are rapidly evolving. In this review, we discuss the developmental mechanisms causing hybrid seed lethality in angiosperms as well as the evolutionary forces establishing endosperm-based postzygotic hybridization barriers.
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| 9. |
- Lafon-Placette, Clément, et al.
(författare)
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Epigenetic mechanisms of postzygotic reproductive isolation in plants
- 2015
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Ingår i: Current Opinion in Plant Biology. - : Elsevier BV. - 1369-5266 .- 1879-0356. ; 23, s. 39-44
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Forskningsöversikt (refereegranskat)abstract
- Hybrid incompatibility is generally viewed as a consequence of negative epistatic interactions between alleles that do not cause negative fitness effects in their parents. Substantial evidence in support of the model has accumulated over recent years. Nevertheless, there is evidence that hybrid incompatibility can have an epigenetic basis and results from deregulated small RNAs (sRNAs), causing changes in DNA methylation and transposable element (TE) activation. Epigenetically regulated loci can impact on the expression of nearby located genes. Alteration of dosage-sensitive gene expression builds hybridization barriers in the endosperm; however, it may also offer an explanation for transgressive effects in plant hybrids. In this review we highlight recent advances that illuminate the role of epigenetic pathways in establishing hybrid incompatibility in plants.
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| 10. |
- Lafon-Placette, Clément, et al.
(författare)
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Methylome of DNase I sensitive chromatin in Populus trichocarpa shoot apical meristematic cells : a simplified approach revealing characteristics of gene-body DNA methylation in open chromatin state
- 2013
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 197:2, s. 416-430
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Tidskriftsartikel (refereegranskat)abstract
- DNA methylation is involved in the control of plant development and adaptation to the environment through modifications of chromatin compaction and gene expression. In poplar (Populus trichocarpa), a perennial plant, variations in DNA methylation have been reported between genotypes and tissues or in response to drought. Nevertheless, the relationships between gene-body DNA methylation, gene expression and chromatin compaction still need clarification.Here, DNA methylation was mapped in the noncondensed chromatin fraction from P. trichocarpa shoot apical meristematic cells, the center of plant morphogenesis, where DNA methylation variations could influence the developmental trajectory. DNase I was used to isolate the noncondensed chromatin fraction. Methylated sequences were immunoprecipitated, sequenced using Illumina/Solexa technology and mapped on the v2.0 poplar genome. Bisulfite sequencing of candidate sequences was used to confirm mapping data and to assess cytosine contexts and methylation levels.While the methylated DNase I hypersensitive site fraction covered 1.9% of the poplar genome, it contained sequences corresponding to 74% of poplar gene models, mostly exons. The level and cytosine context of gene-body DNA methylation varied with the structural characteristics of the genes.Taken together, our data show that DNA methylation is widespread and variable among genes in open chromatin of meristematic cells, in agreement with a role in their developmental trajectory.
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