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P. J. Van Dijk - One of the best experts on this subject based on the ideXlab platform.
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ecological and evolutionary opportunities of apomixis insights from taraxacum and chondrilla
Philosophical Transactions of the Royal Society B, 2003Co-Authors: P. J. Van DijkAbstract:The ecological and evolutionary opportunities of apomixis in the short and the long term are considered, based on two closely related Apomictic genera: Taraxacum (dandelion) and Chondrilla (skeleton weed). In both genera Apomicts have a wider geographical distribution than sexuals, illustrating the short-term ecological success of apomixis. Allozymes and DNA markers indicate that Apomictic populations are highly polyclonal. In Taraxacum, clonal diversity can be generated by rare hybridization between sexuals and Apomicts, the latter acting as pollen donors. Less extensive clonal diversity is generated by mutations within clonal lineages. Clonal diversity may be maintained by frequency-dependent selection, caused by biological interactions (e.g. competitors and pathogens). Some clones are geographically widespread and probably represent phenotypically plastic 'general-purpose genotypes'. The long-term evolutionary success of Apomictic clones may be limited by lack of adaptive potential and the accumulation of deleterious mutations. Although Apomictic clones may be considered as 'evolutionary dead ends', the genes controlling apomixis can escape from degeneration and extinction via pollen in crosses between sexuals and Apomicts. In this way, apomixis genes are transferred to a new genetic background, potentially adaptive and cleansed from linked deleterious mutations. Consequently, apomixis genes can be much older than the clones they are currently contained in. The close phylogenetic relationship between Taraxacum and Chondrilla and the similarity of their apomixis mechanisms suggest that apomixis in these two genera could be of common ancestry.
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Comparative cyto-embryological investigations of sexual and Apomictic dandelions (Taraxacum) and their Apomictic hybrids
Sexual Plant Reproduction, 2002Co-Authors: Peter Van Baarlen, Hans De Jong, P. J. Van DijkAbstract:In the autonomous Apomictic Taraxacum offinale (common dandelion), parthenogenetic egg cells develop into embryos and central cells into endosperm without prior fertilisation. Unreduced (2n) megaspores are formed via meiotic diplospory, a nonreductional type of meiosis. In this paper, we describe the normal developmental pathways of sexual and Apomictic reproduction and compare these with the development observed in the Apomictic hybrids. In sexual diploids, a standard type of megasporogenesis and embryo sac development is synchronised between florets in individual capitula. In contrast, we observed that megasporogenesis and gametogenesis proceeded asynchronously between florets within a single capitulum of natural triploid Apomicts. In addition, autonomous endosperm and embryo development initiated independently within individual florets. Parthenogenetic initiation of embryo development in outdoor Apomicts was found to be temperature-dependent. Egg cells produced in natural Apomicts were not fertilised after pollination with haploid pollen grains although pollen tubes were observed to grow into their embryo sacs. Both reductional and diplosporous megasporogenesis were observed in individual inflorescences of triploid Apomictic hybrids. Embryo and endosperm development initiated independently in natural and hybrid Apomicts. [KEYWORDS: apomixis, autonomous endosperm, diplospory embryo, development, parthenogenesis]
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Meiotic recombination in sexual diploid and Apomictic triploid dandelions (Taraxacum officinale L.).
Genome, 2000Co-Authors: P. Van Baarlen, P. J. Van Dijk, R. F. Hoekstra, J. H. De JongAbstract:Taraxacum officinale L. (dandelion) is a vigorous weed in Europe with diploid sexual populations in the southern regions and partially overlapping populations of diploid sexuals and triploid or tetraploid Apomicts in the central and northern regions. Previous studies have demonstrated unexpectedly high levels of genetic variation in the Apomictic populations, suggesting the occurrence of genetic segregation in the Apomicts and (or) hybridization between sexual and Apomictic individuals. In this study we analysed meiosis in both sexual diploid and Apomictic triploid plants to find mechanisms that could account for the high levels of genetic variation in the Apomicts. Microscopic study of microsporocytes in the triploid Apomicts revealed that the levels of chromosome pairing and chiasma formation at meiotic prophase I were lower than in that of the sexual diploids, but still sufficient to assume recombination between the homologues. Nomarski DIC (differential interference contrast) microscopy of optically cleared megasporocytes in the Apomicts demonstrated incidental formation of tetrads, which suggests that hybridization can occur in triploid Apomicts.
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Meiotic recombination in sexual diploid and Apomictic triploid dandelions (Taraxacum officinale L.)
Genome, 2000Co-Authors: Peter Van Baarlen, P. J. Van Dijk, R. F. Hoekstra, J. H. De JongAbstract:Taraxacum officinale L. (dandelion) is a vigorous weed in Europe with diploid sexual populations in the southern regions and partially overlapping populations of diploid sexuals and triploid or tetraploid Apomicts in the central and northern regions. Previous studies have demonstrated unexpectedly high levels of genetic variation in the Apomictic populations, suggesting the occurrence of genetic segregation in the Apomicts and (or) hybridization between sexual and Apomictic individuals. In this study we analysed meiosis in both sexual diploid and Apomictic triploid plants to find mechanisms that could account for the high levels of genetic variation in the Apomicts. Microscopic study of microsporocytes in the triploid Apomicts revealed that the levels of chromosome pairing and chiasma formation at meiotic prophase I were lower than in that of the sexual diploids, but still sufficient to assume recombination between the homologues. Nomarski DIC (differential interference contrast) microscopy of optically cleared megasporocytes in the Apomicts demonstrated incidental formation of tetrads, which suggests that hybridization can occur in triploid Apomicts. [KEYWORDS: apomixis; autosegregation; diplospory; meiotic recombination; meiotic restitution; subsexual reproduction Genotypic variation; plants
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crosses between sexual and Apomictic dandelions taraxacum ii the breakdown of apomixis
Heredity, 1999Co-Authors: P. J. Van Dijk, Inge C Q Tas, Matthieu Falque, Tanja BakxschotmanAbstract:Some dandelions are diplosporous gametophytic Apomicts. In order to study the inheritance and breakdown of apomixis, crosses were made between diploid sexuals and triploid Apomicts. To investigate their breeding system, four nonApomictic diploid and 10 nonApomictic triploid hybrids were pollinated with diploids and the progenies were analysed. Seed fertility was significantly reduced in two diploid hybrids. Nine triploid hybrids were fertile and could be classified into three types, with respect to the composition of their progenies. Type A produced n+n hybrids. Type B produced either a mixture of n + n and 2n + n hybrids, or a mixture of pseudogamous 2n + 0 Apomicts and 2n + n hybrids. Type C produced exclusively 2n + n hybrids. Inheritance of a microsatellite marker strongly suggested that 2n egg cells in type C plants were produced by a first division restitution mechanism. As in Apomicts, microsporogenesis in type C plants was reductional. This suggests that type C plants are diplosporous plants that lack parthenogenesis. Such plants are very rare in other Apomictic plant species. It is concluded that ‘elements of apomixis’, diplospory and parthenogenesis, can be uncoupled. This is inconsistent with the single-locus model for apomixis in Taraxacum as suggested by Mogie (1992). Instead, our results suggest that several loci are involved in the genetic control of apomixis in Taraxacum.
Timothy F. Sharbel - One of the best experts on this subject based on the ideXlab platform.
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Chasing the Apomictic Factors in the Ranunculus auricomus Complex: Exploring Gene Expression Patterns in Microdissected Sexual and Apomictic Ovules.
Genes, 2020Co-Authors: Marco Pellino, Elvira Horandl, Diego Hojsgaard, Timothy F. SharbelAbstract:Apomixis, the asexual reproduction via seeds, is associated to polyploidy and hybridization. To identify possible signatures of apomixis, and possible candidate genes underlying the shift from sex to apomixis, microarray-based gene expression patterns of live microdissected ovules at four different developmental stages were compared between Apomictic and sexual individuals of the Ranunculus auricomus complex. Following predictions from previous work on mechanisms underlying apomixis penetrance and expressivity in the genus, gene expression patterns were classified into three categories based on their relative expression in Apomicts compared to their sexual parental ancestors. We found evidence of misregulation and differential gene expression between Apomicts and sexuals, with the highest number of differences detected during meiosis progression and emergence of aposporous initial (AI) cells, a key developmental stage in the ovule of Apomicts where a decision between divergent reproductive pathways takes place. While most of the differentially expressed genes (DEGs) could not be annotated, gene expression was classified into transgressive, parent of origin and ploidy effects. Genes related to gametogenesis and meiosis demonstrated patterns reflective of transgressive and genome dosage effects, which support the hypothesis of a dominant factor controlling apomixis in Ranunculus and modulated by secondary modifiers. Three genes with probable functions in sporogenesis and gametogenesis development are identified and characterized for future studies.
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Hybridization drives evolution of Apomicts in Rubus subgenus Rubus: evidence from microsatellite markers.
Annals of botany, 2017Co-Authors: Petra Šarhanová, Timothy F. Sharbel, Radim J. Vašut, Martin Dančák, Michal Sochor, Bohumil TrávníčekAbstract:Background and Aims Rubus subgenus Rubus is a group of mostly Apomictic and polyploid species with a complicated taxonomy and history of ongoing hybridization. The only polyploid series with prevailing sexuality is the series Glandulosi , although the Apomictic series Discolores and Radula also retain a high degree of sexuality, which is influenced by environmental conditions and/or pollen donors. The aim of this study is to detect sources of genetic variability, determine the origin of Apomictic taxa and validate microsatellite markers by cloning and sequencing. Methods A total of 206 individuals from two central European regions were genotyped for 11 nuclear microsatellite loci and the chloroplast trn L- trn F region. Microsatellite alleles were further sequenced in order to determine the exact repeat number and to detect size homoplasy due to insertions/deletions in flanking regions. Key Results The results confirm that Apomictic microspecies of ser. Radula are derived from crosses between sexual series Glandulosi and Apomictic series Discolores , whereby the Apomict acts as pollen donor. Each Apomictic microspecies is derived from a single distinct genotype differing from the parental taxa, suggesting stabilized clonal reproduction. Intraspecific variation within Apomicts is considerably low compared with sexual series Glandulosi , and reflects somatic mutation accumulation. While facultative Apomicts produce clonal offspring, sexual species are the conduits of origin for new genetically different Apomictic lineages. Conclusions One of the main driving forces of evolution and speciation in the highly Apomictic subgenus Rubus in central Europe is sexuality in the series Glandulosi . Palaeovegetation data suggest that initial hybridizations took place over different time periods in the two studied regions, and that the successful origin and spread of Apomictic microspecies of the series Radula took place over several millennia. Additionally, the cloning and sequencing show that standard evaluations of microsatellite repeat numbers underestimate genetic variability considering homoplasy in allele size.
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Mutation Accumulation in an Asexual Relative of Arabidopsis.
PLoS genetics, 2017Co-Authors: John T. Lovell, Robert J. Williamson, Stephen I. Wright, John K. Mckay, Timothy F. SharbelAbstract:Asexual populations experience weaker responses to natural selection, which causes deleterious mutations to accumulate over time. Additionally, stochastic loss of individuals free of deleterious mutations can lead to an irreversible increase in mutational load in asexuals (the “click” in Muller’s Ratchet). Here we report on the genomic divergence and distribution of mutations across eight sympatric pairs of sexual and Apomictic (asexual) Boechera (Brassicaceae) genotypes. We show that Apomicts harbor a greater number of derived mutations than sympatric sexual genotypes. Furthermore, in phylogenetically constrained sites that are subject to contemporary purifying selection, the ancestral, conserved allele is more likely to be retained in sexuals than Apomicts. These results indicate that Apomictic lineages accumulate mutations at otherwise conserved sites more often than sexuals, and support the conclusion that deleterious mutation accumulation can be a powerful force in the evolution of asexual higher plants.
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Copy Number Variation in Transcriptionally Active Regions of Sexual and Apomictic Boechera Demonstrates Independently Derived Apomictic Lineages
The Plant cell, 2013Co-Authors: Olawale Mashood Aliyu, Michael Seifert, José M. Corral, Joerg Fuchs, Timothy F. SharbelAbstract:In asexual (Apomictic) plants, the absence of meiosis and sex is expected to lead to mutation accumulation. To compare mutation accumulation in the transcribed genomic regions of sexual and Apomictic plants, we performed a double-validated analysis of copy number variation (CNV) on 10 biological replicates each of diploid sexual and diploid Apomictic Boechera, using a high-density (>700 K) custom microarray. The Boechera genome demonstrated higher levels of depleted CNV, compared with enriched CNV, irrespective of reproductive mode. Genome-wide patterns of CNV revealed four divergent lineages, three of which contain both sexual and Apomictic genotypes. Hence genome-wide CNV reflects at least three independent origins (i.e., expression) of apomixis from different sexual genetic backgrounds. CNV distributions for different families of transposable elements were lineage specific, and the enrichment of LINE/L1 and long term repeat/Copia elements in lineage 3 Apomicts is consistent with sex and meiosis being mechanisms for purging genomic parasites. We hypothesize that significant overrepresentation of specific gene ontology classes (e.g., pollen–pistil interaction) in Apomicts implies that gene enrichment could be an adaptive mechanism for genome stability in diploid Apomicts by providing a polyploid-like system for buffering the effects of deleterious mutations.
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Differential effects of polyploidy and diploidy on fitness of Apomictic Boechera
Sexual Plant Reproduction, 2012Co-Authors: Marie-luise Voigt-zielinski, Marcin Piwczyński, Timothy F. SharbelAbstract:The co-occurrence of apomixis (asexual reproduction) and polyploidy in plants has been the subject of debate in regard to the origin and evolution of asexuality. In recent years, polyploidy has been postulated as a maintenance and stabilization factor rather than as a source of apomixis origin. It is assumed polyploidy facilitates the compensation for mutation accumulation, and hence, the rare occurrence of diploid apomixis indirectly supports this finding. Nevertheless, diploid Apomicts exist and are successful, especially in the genus Boechera . While comparing phenotypic traits, fitness-related traits and apomixis penetrance between both diploid and triploid Apomicts in the genus Boechera , it was expected to find trait variance that can be attributed to ploidy. Surprisingly, little trait variation could be assigned to ploidy, but rather trait variations were mainly genotype-specific. Additionally, it is shown that paternal contribution is very important for trait success, even though all offspring are genetically identical to the mother plant. This harbors implications for the introduction of apomixis into crop plants, considering the effects of paternal contribution during asexual reproduction. Nevertheless, polyploidy is an efficient way to buffer deleterious mutations, but the flexibility of diploid Apomicts of the genus Boechera for rare sexual events contributes to their success in nature.
Gerdien De Jong - One of the best experts on this subject based on the ideXlab platform.
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The effect of intra‐specific competition on seedlings of sexual and Apomictic Taraxacum officinale
Oikos, 2001Co-Authors: Carolien G.f. De Kovel, Gerdien De JongAbstract:Because of their higher evolvability, sexuals may have an advantage relative to asexual organisms in a competitive environment with many biotic interactions. We tested this idea using sexual and Apomictic Taraxacum, dandelions. Taraxacum seedlings were grown without competition and in different competing combinations in a greenhouse. Apomicts had more and longer leaves than sexuals, but the same dry weight at harvest as sexuals. Competition reduced growth to the same extent in both Apomicts and sexuals. Therefore, we conclude that sexual dandelions are no superior competitors relative to Apomicts. In Taraxacum, new Apomictic lineages spin off from the sexual population with some unknown frequency. This may enable the Apomictic community to keep up with the sexual population.
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Responses of Sexual and Apomictic Genotypes of Taraxacum officinale to Variation in Light
Plant Biology, 1999Co-Authors: Carolien G.f. De Kovel, Gerdien De JongAbstract:: The mode of reproduction, sexual or asexual, will influence the way populations respond to selective pressures. This can cause genetic and ecological divergence between sexual and asexual forms of the same species. Here we examine differences in morphology and phenology between sexual and Apomictic types of dandelion, Taraxacum officinale. Sexual and Apomictic dandelions were collected from a mixed population on the banks of the river Rhine, The Netherlands. Clonal copies of both sexual and Apomictic genotypes were planted in an experimental garden under two light levels. Sexual plants flowered four days later on average than Apomicts, but the number of capitula was the same. Apomicts had longer leaves and were heavier than sexual plants, especially under shaded conditions. In Apomicts plasticity for leaf length and height was larger than in sexuals, but for most other measured traits no differences in plasticity were observed. Trait values of Apomicts were within the same range as those of sexual plants.
J M M Van Damme - One of the best experts on this subject based on the ideXlab platform.
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The role of tetraploids in the sexual-asexual cycle in dandelions (Taraxacum).
Heredity, 2004Co-Authors: Marije H. Verduijn, P. J. Van Dijk, J M M Van DammeAbstract:Apomictic plants often produce pollen that can function in crosses with related sexuals. Moreover, facultative Apomicts can produce some sexual offspring. In dandelions, Taraxacum, a sexual-asexual cycle between diploid sexuals and triploid Apomicts, has been described, based on experimental crosses and population genetic studies. Little is known about the actual hybridization processes in nature. We therefore studied the sexual-asexual cycle in a mixed dandelion population in the Netherlands. In this population, the frequencies of sexual diploids and triploids were 0.31 and 0.68, respectively. In addition, less than 1% tetraploids were detected. Diploids were strict sexuals, triploids were obligate Apomicts, but tetraploids were most often only partly Apomictic, lacking certain elements of apomixis. Tetraploid seed fertility in the field was significantly lower than that of Apomictic triploids. Field-pollinated sexual diploids produced on average less than 2% polyploid offspring, implying that the effect of hybridization in the 2x-3x cycle in Taraxacum will be low. Until now, 2x-3x crosses were assumed to be the main pathway of new formation of triploid Apomicts in the sexual-asexual cycle in Taraxacum. However, tetraploid pollen donors produced 28 times more triploid offspring in experimental crosses with diploid sexuals than triploid pollen donors. Rare tetraploids may therefore act as an important bridge in the formation of new triploid Apomicts.
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Nuclear–Cytoplasmic male-sterility in diploid dandelions
Heredity, 2004Co-Authors: R. G. M. Van Der Hulst, Patrick G. Meirmans, P.h. Van Tienderen, J M M Van DammeAbstract:Male-sterility was found in diploid dandelions from two widely separated populations from France, and its inheritance was analysed by crossing a diploid male-sterile dandelion to diploid sexuals and triploid Apomicts. Nuclear genetic variation, found in full-sib families, segregated for male-fertility, partial male-sterility, and full male-sterility, and also segregated for small-sized versus normally sized pollen. The crossing results are best explained by a cytoplasmic male-sterility factor in combination with two dominant restorer genes. Involvement of the cytoplasmic male-sterility factor was further investigated by chloroplast haplotyping. Male-sterility was exclusively associated with a rare chloroplast haplotype (designated 16b). This haplotype was found in seven male-sterile plants and one (apparently restored) male-fertile individual but does not occur in 110 co-existing male-fertile plants and not in several hundreds of individuals previously haplotyped. Apomicts with cytoplasmic male sterility were generated in some test crosses. This raises the question as to whether the male sterility found in natural dandelion Apomicts, is of cytoplasmic or of nuclear genetic nature. As many breeding systems in Taraxacum are involved in shaping population structure, it will be difficult to predict the evolutionary consequences of nuclear-cytoplasmic male-sterility for this species complex.
Ueli Grossniklaus - One of the best experts on this subject based on the ideXlab platform.
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Apomictic and Sexual Germline Development Differ with Respect to Cell Cycle, Transcriptional, Hormonal and Epigenetic Regulation
2016Co-Authors: Anja Schmidt, Marc W. Schmid, Ulrich C. Klostermeier, Christian Sailer, Manuel Waller, Philip Rosenstiel, Ueli GrossniklausAbstract:Seeds of flowering plants can be formed sexually or asexually through apomixis. Apomixis occurs in about 400 species and is of great interest for agriculture as it produces clonal offspring. It differs from sexual reproduction in three major aspects: (1) While the sexual megaspore mother cell (MMC) undergoes meiosis, the Apomictic initial cell (AIC) omits or aborts meiosis (apomeiosis); (2) the unreduced egg cell of Apomicts forms an embryo without fertilization (parthenogenesis); and (3) the formation of functional endosperm requires specific developmental adaptations. Currently, our knowledge about the gene regulatory programs underlying apomixis is scarce. We used the Apomict Boechera gunnisoniana, a close relative of Arabidopsis thaliana, to investigate the transcriptional basis underlying apomeiosis and parthenogenesis. Here, we present the first comprehensive reference transcriptome for reproductive development in an Apomict. To compare sexual and Apomictic development at the cellular level, we used laser-assisted microdissection combined with microarray and RNA-Seq analyses. Conservation of enriched gene ontologies between the AIC and the MMC likely reflects functions of importance to germline initiation, illustrating the close developmental relationship of sexuality and apomixis. However, several regulatory pathways differ between sexual and Apomictic germlines, including cell cycle control, hormonal pathways, epigenetic and transcriptional regulation. Enrichment of specific signal transduction pathways are a feature of the Apomictic germline, as is spermidine metabolism, which is associated with somatic embryogenesis in various plants. Our study provides
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Apomictic and sexual germline development differ with respect to cell cycle transcriptional hormonal and epigenetic regulation
PLOS Genetics, 2014Co-Authors: Anja Schmidt, Marc W. Schmid, Ulrich C. Klostermeier, Christian Sailer, Manuel Waller, Philip Rosenstiel, Weihong Qi, Daniela Guthorl, Ueli GrossniklausAbstract:Seeds of flowering plants can be formed sexually or asexually through apomixis. Apomixis occurs in about 400 species and is of great interest for agriculture as it produces clonal offspring. It differs from sexual reproduction in three major aspects: (1) While the sexual megaspore mother cell (MMC) undergoes meiosis, the Apomictic initial cell (AIC) omits or aborts meiosis (apomeiosis); (2) the unreduced egg cell of Apomicts forms an embryo without fertilization (parthenogenesis); and (3) the formation of functional endosperm requires specific developmental adaptations. Currently, our knowledge about the gene regulatory programs underlying apomixis is scarce. We used the Apomict Boechera gunnisoniana, a close relative of Arabidopsis thaliana, to investigate the transcriptional basis underlying apomeiosis and parthenogenesis. Here, we present the first comprehensive reference transcriptome for reproductive development in an Apomict. To compare sexual and Apomictic development at the cellular level, we used laser-assisted microdissection combined with microarray and RNA-Seq analyses. Conservation of enriched gene ontologies between the AIC and the MMC likely reflects functions of importance to germline initiation, illustrating the close developmental relationship of sexuality and apomixis. However, several regulatory pathways differ between sexual and Apomictic germlines, including cell cycle control, hormonal pathways, epigenetic and transcriptional regulation. Enrichment of specific signal transduction pathways are a feature of the Apomictic germline, as is spermidine metabolism, which is associated with somatic embryogenesis in various plants. Our study provides a comprehensive reference dataset for Apomictic development and yields important new insights into the transcriptional basis underlying apomixis in relation to sexual reproduction.
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sexual hieracium pilosella plants are better inter specific while Apomictic plants are better intra specific competitors
Perspectives in Plant Ecology Evolution and Systematics, 2014Co-Authors: Christian Sailer, Bernhard Schmid, Jurg Stocklin, Ueli GrossniklausAbstract:Abstract Apomixis, asexual reproduction through seeds, occurs in over 40 plant families. This widespread phenomenon can lead to the fixation of successful genotypes, resulting in a fitness advantage. On the other hand, Apomicts are expected to lose their fitness advantage if the environment changes because of their limited evolutionary potential, which is due to low genetic variability and the potential accumulation of deleterious somatic mutations. Nonetheless, some Apomicts have been extremely successful, for example certain Apomictic accessions of Hieracium pilosella L. from New Zealand, where the plant is invasive. Here, we investigate whether the success of these Apomictic accessions could be due to a fitness advantage by comparing the vegetative competitiveness of Apomictic H. pilosella from New Zealand with sexual accessions of H. pilosella from Europe. Sexual and Apomictic plants were grown either (A) alone (no competition), (B) in competition with the other type (intra-specific competition), (C) in competition with the grass Bromus erectus (inter-specific competition), and (D) in competition with the other type and the grass B. erectus (intra- and inter-specific competition). To distinguish effects of apomixis and the region of origin, different H. pilosella lineages were compared. Furthermore, experiments were carried out to investigate effects of the ploidy level. We show that sexual plants are better inter-specific competitors than Apomicts in terms of vegetative reproduction (number of stolons) and vegetative spread (stolon length), while Apomicts do better than sexuals in intra-specific competition. The magnitude of the effect was in some cases dependent on the ploidy levels of the plants. Furthermore, Apomicts always produced more stolons than sexuals, suggesting potential displacement of sexuals by Apomicts where they co-occur.