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Anna M Koltunow - One of the best experts on this subject based on the ideXlab platform.

  • evolution of Apomixis loci in pilosella and hieracium asteraceae inferred from the conservation of Apomixis linked markers in natural and experimental populations
    Heredity, 2015
    Co-Authors: Melanie L Hand, Susan D Johnson, Hayley Siddons, Karsten Oelkers, Jindřich Chrtek, Judith Fehrer, Anna Krahulcova, Anna M Koltunow
    Abstract:

    The Hieracium and Pilosella (Lactuceae, Asteraceae) genera of closely related hawkweeds contain species with two different modes of gametophytic Apomixis (asexual seed formation). Both genera contain polyploid species, and in wild populations, sexual and apomictic species co-exist. Apomixis is known to co-exist with sexuality in apomictic Pilosella individuals, however, apomictic Hieracium have been regarded as obligate apomicts. Here, a developmental analysis of Apomixis within 16 Hieracium species revealed meiosis and megaspore tetrad formation in 1 to 7% of ovules, for the first time indicating residual sexuality in this genus. Molecular markers linked to the two independent, dominant loci LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP) controlling Apomixis in Pilosella piloselloides subsp. praealta were screened across 20 phenotyped Hieracium individuals from natural populations, and 65 phenotyped Pilosella individuals from natural and experimental cross populations, to examine their conservation, inheritance and association with reproductive modes. All of the tested LOA and LOP-linked markers were absent in the 20 Hieracium samples irrespective of their reproductive mode. Within Pilosella, LOA and LOP-linked markers were essentially absent within the sexual plants, although they were not conserved in all apomictic individuals. Both loci appeared to be inherited independently, and evidence for additional genetic factors influencing quantitative expression of LOA and LOP was obtained. Collectively, these data suggest independent evolution of Apomixis in Hieracium and Pilosella and are discussed with respect to current knowledge of the evolution of Apomixis.

  • the loss of apomeiosis loa locus in hieracium praealtum can function independently of the associated large scale repetitive chromosomal structure
    New Phytologist, 2014
    Co-Authors: Yoshiko Kotani, Susan D Johnson, Hayley Siddons, Yasuhiko Mukai, Takashi Okada, Go Suzuki, Steven T Henderson, Anna M Koltunow
    Abstract:

    Summary Apomixis or asexual seed formation in Hieracium praealtum (Asteraceae) is controlled by two independent dominant loci. One of these, the LOSS OF APOMEIOSIS (LOA) locus, controls Apomixis initiation, mitotic embryo sac formation (apospory) and suppression of the sexual pathway. The LOA locus is found near the end of a hemizygous chromosome surrounded by extensive repeats extending along the chromosome arm. Similar Apomixis-carrying chromosome structures have been found in some apomictic grasses, suggesting that the extensive repetitive sequences may be functionally relevant to Apomixis. Fluorescence in situ hybridization (FISH) was used to examine chromosomes of apomeiosis deletion mutants and rare recombinants in the critical LOA region arising from a cross between sexual Hieracium pilosella and apomictic H. praealtum. The combined analyses of aposporous and nonaposporous recombinant progeny and chromosomal karyotypes were used to determine that the functional LOA locus can be genetically separated from the very extensive repeat regions found on the LOA-carrying chromosome. The large-scale repetitive sequences associated with the LOA locus in H. praealtum are not essential for apospory or suppression of sexual megasporogenesis (female meiosis).

  • sexual reproduction is the default mode in apomictic hieracium subgenus pilosella in which two dominant loci function to enable Apomixis
    Plant Journal, 2011
    Co-Authors: Anna M Koltunow, Susan D Johnson, Takashi Okada, Go Suzuki, Julio C M Rodrigues, Yingkao Hu, Tohru Tsuchiya, Saira Wilson, Pam Fletcher, Yasuhiko Mukai
    Abstract:

    Summary Asexual seed formation, or Apomixis, in the Hieracium subgenus Pilosella is controlled by two dominant independent genetic loci, LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP). We examined Apomixis mutants that had lost function in one or both loci to establish their developmental roles during seed formation. In apomicts, sexual reproduction is initiated first. Somatic aposporous initial (AI) cells differentiate near meiotic cells, and the sexual pathway is terminated as AI cells undergo mitotic embryo sac formation. Seed initiation is fertilization-independent. Using a partially penetrant cytotoxic reporter to inhibit meioisis, we showed that developmental events leading to the completion of meiotic tetrad formation are required for AI cell formation. Sexual initiation may therefore stimulate activity of the LOA locus, which was found to be required for AI cell formation and subsequent suppression of the sexual pathway. AI cells undergo nuclear division to form embryo sacs, in which LOP functions gametophytically to stimulate fertilization-independent embryo and endosperm formation. Loss of function in either locus results in partial reversion to sexual reproduction, and loss of function in both loci results in total reversion to sexual reproduction. Therefore, in these apomicts, sexual reproduction is the default reproductive mode upon which Apomixis is superimposed. These loci are unlikely to encode genes essential for sexual reproduction, but may function to recruit the sexual machinery at specific time points to enable Apomixis.

  • sexual and apomictic reproduction in hieracium subgenus pilosella are closely interrelated developmental pathways
    The Plant Cell, 2003
    Co-Authors: Matthew R Tucker, Anaclaudia G Araujo, Valerie Hecht, E D L Schmidt, Janbart Rossell, Sacco C. De Vries, Nicholas A Paech, Anna M Koltunow
    Abstract:

    Seed formation in flowering plants requires meiosis of the megaspore mother cell (MMC) inside the ovule, selection of a megaspore that undergoes mitosis to form an embryo sac, and double fertilization to initiate embryo and endosperm formation. During Apomixis, or asexual seed formation, in Hieracium ovules, a somatic aposporous initial (AI) cell divides to form a structurally variable aposporous embryo sac and embryo. This entire process, including endosperm development, is fertilization independent. Introduction of reproductive tissue marker genes into sexual and apomictic Hieracium showed that AI cells do not express a MMC marker. Spatial and temporal gene expression patterns of other introduced genes were conserved commencing with the first nuclear division of the AI cell in apomicts and the mitotic initiation of embryo sac formation in sexual plants. Conservation in expression patterns also occurred during embryo and endosperm development, indicating that sexuality and Apomixis are interrelated pathways that share regulatory components. The induction of a modified sexual reproduction program in AI cells may enable the manifestation of Apomixis in Hieracium.

  • Apomixis is not developmentally conserved in related genetically characterized hieracium plants of varying ploidy
    Sexual Plant Reproduction, 2000
    Co-Authors: Anna M Koltunow, Susan D Johnson, Roy Bicknell
    Abstract:

    Apomixis is facultative in characterized members of the genus Hieracium. The three components that comprise the apomictic mechanism include apospory followed by autonomous embryo and endosperm formation. The time of aposporous embryo sac initiation and mode of embryo sac formation are different in Hieracium piloselloides (D3) and Hieracium aurantiacum (A3.4). Genetic studies have shown that a single dominant locus encodes all three components of Apomixis in both species (Bicknell et al. 2000). We histologically examined a range of related, genetically characterized apomictic Hieracium plants derived from D3 and A3.4 to assess conservation of the apomictic mechanism in different genetic backgrounds. The plants varied in ploidy, and also in the amount of DNA introduced from sexual Hieracium pilosella (P4). An apomictic hybrid from a cross between the two apomicts was also examined. The developmental processes observed in the parental apomicts were not conserved in the examined plants and alterations occurred in the components of Apomixis. One plant also exhibited adventitious embryony. The results show that other genetic factors can modify Apomixis with respect to time of initiation, spatial location, and mode of developmental progression. Both the apomictic locus and the modifiers are essential for efficient penetrance of the trait in Hieracium. Some of the findings in Hieracium correspond with observations in Ranunculus and this is discussed in terms of models for apomictic development and the control of Apomixis in crops.

Go Suzuki - One of the best experts on this subject based on the ideXlab platform.

  • generation of an integrated hieracium genomic and transcriptomic resource enables exploration of small rna pathways during Apomixis initiation
    BMC Biology, 2016
    Co-Authors: David S Rabiger, Susan D Johnson, Melanie L Hand, Karsten Oelkers, Steven T Henderson, Jennifer M Taylor, Andrew Spriggs, Maria Hrmova, Keisuke Saito, Go Suzuki
    Abstract:

    Background Application of Apomixis, or asexual seed formation, in crop breeding would allow rapid fixation of complex traits, economizing improved crop delivery. Identification of Apomixis genes is confounded by the polyploid nature, high genome complexity and lack of genomic sequence integration with reproductive tissue transcriptomes in most apomicts.

  • Generation of an integrated Hieracium genomic and transcriptomic resource enables exploration of small RNA pathways during Apomixis initiation
    'Springer Science and Business Media LLC', 2016
    Co-Authors: Rabiger, David S., Taylor, Jennifer M., Spriggs Andrew, Hand, Melanie L., Henderson, Steven T., Johnson, Susan D., Oelkers Karsten, Hrmova Maria, Saito Keisuke, Go Suzuki
    Abstract:

    Background: Application of Apomixis, or asexual seed formation, in crop breeding would allow rapid fixation of complex traits, economizing improved crop delivery. Identification of Apomixis genes is confounded by the polyploid nature, high genome complexity and lack of genomic sequence integration with reproductive tissue transcriptomes in most apomicts. Results: A genomic and transcriptomic resource was developed for Hieracium subgenus Pilosella (Asteraceae) which incorporates characterized sexual, apomictic and mutant apomict plants exhibiting reversion to sexual reproduction. Apomicts develop additional female gametogenic cells that suppress the sexual pathway in ovules. Disrupting small RNA pathways in sexual Arabidopsis also induces extra female gametogenic cells; therefore, the resource was used to examine if changes in small RNA pathways correlate with Apomixis initiation. An initial characterization of small RNA pathway genes within Hieracium was undertaken, and ovary-expressed ARGONAUTE genes were identified and cloned. Comparisons of whole ovary transcriptomes from mutant apomicts, relative to the parental apomict, revealed that differentially expressed genes were enriched for processes involved in small RNA biogenesis and chromatin silencing. Small RNA profiles within mutant ovaries did not reveal large-scale alterations in composition or length distributions; however, a small number of differentially expressed, putative small RNA targets were identified. Conclusions: The established Hieracium resource represents a substantial contribution towards the investigation of early sexual and apomictic female gamete development, and the generation of new candidate genes and markers. Observed changes in small RNA targets and biogenesis pathways within sexual and apomictic ovaries will underlie future functional research into Apomixis initiation in Hieracium

  • the loss of apomeiosis loa locus in hieracium praealtum can function independently of the associated large scale repetitive chromosomal structure
    New Phytologist, 2014
    Co-Authors: Yoshiko Kotani, Susan D Johnson, Hayley Siddons, Yasuhiko Mukai, Takashi Okada, Go Suzuki, Steven T Henderson, Anna M Koltunow
    Abstract:

    Summary Apomixis or asexual seed formation in Hieracium praealtum (Asteraceae) is controlled by two independent dominant loci. One of these, the LOSS OF APOMEIOSIS (LOA) locus, controls Apomixis initiation, mitotic embryo sac formation (apospory) and suppression of the sexual pathway. The LOA locus is found near the end of a hemizygous chromosome surrounded by extensive repeats extending along the chromosome arm. Similar Apomixis-carrying chromosome structures have been found in some apomictic grasses, suggesting that the extensive repetitive sequences may be functionally relevant to Apomixis. Fluorescence in situ hybridization (FISH) was used to examine chromosomes of apomeiosis deletion mutants and rare recombinants in the critical LOA region arising from a cross between sexual Hieracium pilosella and apomictic H. praealtum. The combined analyses of aposporous and nonaposporous recombinant progeny and chromosomal karyotypes were used to determine that the functional LOA locus can be genetically separated from the very extensive repeat regions found on the LOA-carrying chromosome. The large-scale repetitive sequences associated with the LOA locus in H. praealtum are not essential for apospory or suppression of sexual megasporogenesis (female meiosis).

  • sexual reproduction is the default mode in apomictic hieracium subgenus pilosella in which two dominant loci function to enable Apomixis
    Plant Journal, 2011
    Co-Authors: Anna M Koltunow, Susan D Johnson, Takashi Okada, Go Suzuki, Julio C M Rodrigues, Yingkao Hu, Tohru Tsuchiya, Saira Wilson, Pam Fletcher, Yasuhiko Mukai
    Abstract:

    Summary Asexual seed formation, or Apomixis, in the Hieracium subgenus Pilosella is controlled by two dominant independent genetic loci, LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP). We examined Apomixis mutants that had lost function in one or both loci to establish their developmental roles during seed formation. In apomicts, sexual reproduction is initiated first. Somatic aposporous initial (AI) cells differentiate near meiotic cells, and the sexual pathway is terminated as AI cells undergo mitotic embryo sac formation. Seed initiation is fertilization-independent. Using a partially penetrant cytotoxic reporter to inhibit meioisis, we showed that developmental events leading to the completion of meiotic tetrad formation are required for AI cell formation. Sexual initiation may therefore stimulate activity of the LOA locus, which was found to be required for AI cell formation and subsequent suppression of the sexual pathway. AI cells undergo nuclear division to form embryo sacs, in which LOP functions gametophytically to stimulate fertilization-independent embryo and endosperm formation. Loss of function in either locus results in partial reversion to sexual reproduction, and loss of function in both loci results in total reversion to sexual reproduction. Therefore, in these apomicts, sexual reproduction is the default reproductive mode upon which Apomixis is superimposed. These loci are unlikely to encode genes essential for sexual reproduction, but may function to recruit the sexual machinery at specific time points to enable Apomixis.

Peggy Oziasakins - One of the best experts on this subject based on the ideXlab platform.

  • recombination within the apospory specific genomic region leads to the uncoupling of Apomixis components in cenchrus ciliaris
    Planta, 2013
    Co-Authors: Joann A Conner, Gunawati Gunawan, Peggy Oziasakins
    Abstract:

    Apomixis enables the clonal propagation of maternal genotypes through seed. If Apomixis could be harnessed via genetic engineering or introgression, it would have a major economic impact for agricultural crops. In the grass species Pennisetum squamulatum and Cenchrus ciliaris (syn. P. ciliare), Apomixis is controlled by a single dominant “locus”, the apospory-specific genomic region (ASGR). For P. squamulatum, 18 published sequenced characterized amplified region (SCAR) markers have been identified which always co-segregate with apospory. Six of these markers are conserved SCARs in the closely related species, C. ciliaris and co-segregate with the trait. A screen of progeny from a cross of sexual × apomictic C. ciliaris genotypes identified a plant, A8, retaining two of the six ASGR-linked SCAR markers. Additional and newly identified ASGR-linked markers were generated to help identify the extent of recombination within the ASGR. Based on analysis of missing markers, the A8 recombinant plant has lost a significant portion of the ASGR but continues to form aposporous embryo sacs. Seedlings produced from aposporous embryo sacs are 6× in ploidy level and hence the A8 recombinant does not express parthenogenesis. The recombinant A8 plant represents a step forward in reducing the complexity of the ASGR locus to determine the factor(s) required for aposporous embryo sac formation and documents the separation of expression of the two components of Apomixis in C. ciliaris.

  • pennisetum squamulatum is the predominant cytotype hexaploid or octaploid
    Journal of Heredity, 2006
    Co-Authors: Yukio Akiyama, Wayne W. Hanna, Shailendra Goel, Zhenbang Chen, Peggy Oziasakins
    Abstract:

    Apomixis is a mode of asexual reproduction where maternal clones are produced through seeds. Consequently, genetic segregation is prevented in hybrid progenies. Pennisetum squamulatum has been used to transfer Apomixis into the related sexual species Pennisetum glaucum by the introgression of an apospory-specific genomic region (ASGR)-carrier chromosome. Crosses between P. glaucum and P. squamulatum or Pennisetum purpureum have been relatively easy to make even though P. squamulatum has been reported to have a different basic chromosome number than the other 2 species (9 vs. 7) and to be hexaploid (2n = 6x = 54). Our extensive examination of one accession had shown a chromosome number of 2n = 56. In order to determine if there was a variation among accessions, we counted the number of chromosomes in 5 accessions of P. squamulatum using centromeric and 18S-5.8S-26S rDNA probes as molecular cytological markers. Our results showed that P. squamulatum is most likely octaploid with a basic chromosome number of 7 (2n = 8x = 56) and may belong to the secondary gene pool of Pennisetum. Moreover, a morphologically similar ASGR-carrier chromosome that confers Apomixis was observed in all accessions.

  • high resolution physical mapping in pennisetum squamulatum reveals extensive chromosomal heteromorphism of the genomic region associated with Apomixis
    Plant Physiology, 2004
    Co-Authors: Yukio Akiyama, Shailendra Goel, W W Hanna, Joann A Conner, Daryl T Morishige, John E Mullet, Peggy Oziasakins
    Abstract:

    Gametophytic Apomixis is asexual reproduction as a consequence of parthenogenetic development of a chromosomally unreduced egg. The trait leads to the production of embryos with a maternal genotype, i.e. progeny are clones of the maternal plant. The application of the trait in agriculture could be a tremendous tool for crop improvement through conventional and nonconventional breeding methods. Unfortunately, there are no major crops that reproduce by Apomixis, and interspecific hybridization with wild relatives has not yet resulted in commercially viable germplasm. Pennisetum squamulatum is an aposporous apomict from which the gene(s) for Apomixis has been transferred to sexual pearl millet by backcrossing. Twelve molecular markers that are linked with Apomixis coexist in a tight linkage block called the apospory-specific genomic region (ASGR), and several of these markers have been shown to be hemizygous in the polyploid genome of P. squamulatum. High resolution genetic mapping of these markers has not been possible because of low recombination in this region of the genome. We now show the physical arrangement of bacterial artificial chromosomes containing Apomixis-linked molecular markers by high resolution fluorescence in situ hybridization on pachytene chromosomes. The size of the ASGR, currently defined as the entire hemizygous region that hybridizes with Apomixis-linked bacterial artificial chromosomes, was estimated on pachytene and mitotic chromosomes to be approximately 50 Mbp (a quarter of the chromosome). The ASGR includes highly repetitive sequences from an Opie-2-like retrotransposon family that are particularly abundant in this region of the genome.

  • molecular characterization of the genomic region linked with Apomixis in pennisetum cenchrus
    Functional & Integrative Genomics, 2003
    Co-Authors: Peggy Oziasakins, Yukio Akiyama, W W Hanna
    Abstract:

    Apomixis is defined as asexual reproduction through seeds, although this outcome can be achieved by multiple pathways. Since little is known about the molecular control of these pathways, how they might intersect is also a mystery. Two of these pathways in the grass family, diplospory and apospory, are receiving attention from molecular biologists. Apospory in Pennisetum/Cenchrus, two genera of panicoid grasses, results in the formation of four-nucleate embryo sacs that lack antipodals. Sexual reproduction frequently aborts so that the resulting seed is composed of (1) a parthenogenetically derived embryo that is genetically identical to the mother and (2) endosperm formed through pseudogamy. The transmission of Apomixis is associated with the transfer of a linkage block on a single chromosome. This linkage block contains repetitive sequences as well as hemizygous, low-copy DNA sequences. Fluorescence in situ hybridization has demonstrated that these DNA regions occur on only a single chromosome, but not its homologs, in the polyploid apomicts studied. Features of the Apomixis-associated region resemble those of other chromosomal segments isolated from recombination and replete with "selfish" DNAs.

  • tight clustering and hemizygosity of Apomixis linked molecular markers in pennisetum squamulatum implies genetic control of apospory by a divergent locus that may have no allelic form in sexual genotypes
    Proceedings of the National Academy of Sciences of the United States of America, 1998
    Co-Authors: Peggy Oziasakins, Dominique Roche, Wayne W. Hanna
    Abstract:

    Apomixis is a naturally occurring mode of reproduction that results in embryo formation without the involvement of meiosis or fertilization of the egg. Seed-derived progeny of an apomictic plant are genetically identical to the maternal parent. We are studying a form of Apomixis called apospory that occurs in the genus Pennisetum, a taxon in the grass family. A cultivated member of this genus, pearl millet (Pennisetum glaucum), reproduces sexually. A wild relative of pearl millet, Pennisetum squamulatum, that is an obligate aposporous species, is cross-compatible with pearl millet when used as a pollen donor in the interspecific cross. We present herein the genetic mapping of 13 molecular markers in an interspecific hybrid population of 397 individuals that segregates for Apomixis and sexuality. Surprisingly, 12 of the 13 markers strictly cosegregated with aposporous embryo sac development, clearly defining a contiguous apospory-specific genomic region in which no genetic recombination was detected. Lack of or suppression of recombination may be coincidentally associated with the chromosomal context of the Apomixis locus or it may be a consequence of its evolution that is essential for preservation of gene function as has been previously shown in studies of complex loci in both plant and animal species.

Susan D Johnson - One of the best experts on this subject based on the ideXlab platform.

  • generation of an integrated hieracium genomic and transcriptomic resource enables exploration of small rna pathways during Apomixis initiation
    BMC Biology, 2016
    Co-Authors: David S Rabiger, Susan D Johnson, Melanie L Hand, Karsten Oelkers, Steven T Henderson, Jennifer M Taylor, Andrew Spriggs, Maria Hrmova, Keisuke Saito, Go Suzuki
    Abstract:

    Background Application of Apomixis, or asexual seed formation, in crop breeding would allow rapid fixation of complex traits, economizing improved crop delivery. Identification of Apomixis genes is confounded by the polyploid nature, high genome complexity and lack of genomic sequence integration with reproductive tissue transcriptomes in most apomicts.

  • evolution of Apomixis loci in pilosella and hieracium asteraceae inferred from the conservation of Apomixis linked markers in natural and experimental populations
    Heredity, 2015
    Co-Authors: Melanie L Hand, Susan D Johnson, Hayley Siddons, Karsten Oelkers, Jindřich Chrtek, Judith Fehrer, Anna Krahulcova, Anna M Koltunow
    Abstract:

    The Hieracium and Pilosella (Lactuceae, Asteraceae) genera of closely related hawkweeds contain species with two different modes of gametophytic Apomixis (asexual seed formation). Both genera contain polyploid species, and in wild populations, sexual and apomictic species co-exist. Apomixis is known to co-exist with sexuality in apomictic Pilosella individuals, however, apomictic Hieracium have been regarded as obligate apomicts. Here, a developmental analysis of Apomixis within 16 Hieracium species revealed meiosis and megaspore tetrad formation in 1 to 7% of ovules, for the first time indicating residual sexuality in this genus. Molecular markers linked to the two independent, dominant loci LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP) controlling Apomixis in Pilosella piloselloides subsp. praealta were screened across 20 phenotyped Hieracium individuals from natural populations, and 65 phenotyped Pilosella individuals from natural and experimental cross populations, to examine their conservation, inheritance and association with reproductive modes. All of the tested LOA and LOP-linked markers were absent in the 20 Hieracium samples irrespective of their reproductive mode. Within Pilosella, LOA and LOP-linked markers were essentially absent within the sexual plants, although they were not conserved in all apomictic individuals. Both loci appeared to be inherited independently, and evidence for additional genetic factors influencing quantitative expression of LOA and LOP was obtained. Collectively, these data suggest independent evolution of Apomixis in Hieracium and Pilosella and are discussed with respect to current knowledge of the evolution of Apomixis.

  • the loss of apomeiosis loa locus in hieracium praealtum can function independently of the associated large scale repetitive chromosomal structure
    New Phytologist, 2014
    Co-Authors: Yoshiko Kotani, Susan D Johnson, Hayley Siddons, Yasuhiko Mukai, Takashi Okada, Go Suzuki, Steven T Henderson, Anna M Koltunow
    Abstract:

    Summary Apomixis or asexual seed formation in Hieracium praealtum (Asteraceae) is controlled by two independent dominant loci. One of these, the LOSS OF APOMEIOSIS (LOA) locus, controls Apomixis initiation, mitotic embryo sac formation (apospory) and suppression of the sexual pathway. The LOA locus is found near the end of a hemizygous chromosome surrounded by extensive repeats extending along the chromosome arm. Similar Apomixis-carrying chromosome structures have been found in some apomictic grasses, suggesting that the extensive repetitive sequences may be functionally relevant to Apomixis. Fluorescence in situ hybridization (FISH) was used to examine chromosomes of apomeiosis deletion mutants and rare recombinants in the critical LOA region arising from a cross between sexual Hieracium pilosella and apomictic H. praealtum. The combined analyses of aposporous and nonaposporous recombinant progeny and chromosomal karyotypes were used to determine that the functional LOA locus can be genetically separated from the very extensive repeat regions found on the LOA-carrying chromosome. The large-scale repetitive sequences associated with the LOA locus in H. praealtum are not essential for apospory or suppression of sexual megasporogenesis (female meiosis).

  • sexual reproduction is the default mode in apomictic hieracium subgenus pilosella in which two dominant loci function to enable Apomixis
    Plant Journal, 2011
    Co-Authors: Anna M Koltunow, Susan D Johnson, Takashi Okada, Go Suzuki, Julio C M Rodrigues, Yingkao Hu, Tohru Tsuchiya, Saira Wilson, Pam Fletcher, Yasuhiko Mukai
    Abstract:

    Summary Asexual seed formation, or Apomixis, in the Hieracium subgenus Pilosella is controlled by two dominant independent genetic loci, LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP). We examined Apomixis mutants that had lost function in one or both loci to establish their developmental roles during seed formation. In apomicts, sexual reproduction is initiated first. Somatic aposporous initial (AI) cells differentiate near meiotic cells, and the sexual pathway is terminated as AI cells undergo mitotic embryo sac formation. Seed initiation is fertilization-independent. Using a partially penetrant cytotoxic reporter to inhibit meioisis, we showed that developmental events leading to the completion of meiotic tetrad formation are required for AI cell formation. Sexual initiation may therefore stimulate activity of the LOA locus, which was found to be required for AI cell formation and subsequent suppression of the sexual pathway. AI cells undergo nuclear division to form embryo sacs, in which LOP functions gametophytically to stimulate fertilization-independent embryo and endosperm formation. Loss of function in either locus results in partial reversion to sexual reproduction, and loss of function in both loci results in total reversion to sexual reproduction. Therefore, in these apomicts, sexual reproduction is the default reproductive mode upon which Apomixis is superimposed. These loci are unlikely to encode genes essential for sexual reproduction, but may function to recruit the sexual machinery at specific time points to enable Apomixis.

  • Apomixis is not developmentally conserved in related genetically characterized hieracium plants of varying ploidy
    Sexual Plant Reproduction, 2000
    Co-Authors: Anna M Koltunow, Susan D Johnson, Roy Bicknell
    Abstract:

    Apomixis is facultative in characterized members of the genus Hieracium. The three components that comprise the apomictic mechanism include apospory followed by autonomous embryo and endosperm formation. The time of aposporous embryo sac initiation and mode of embryo sac formation are different in Hieracium piloselloides (D3) and Hieracium aurantiacum (A3.4). Genetic studies have shown that a single dominant locus encodes all three components of Apomixis in both species (Bicknell et al. 2000). We histologically examined a range of related, genetically characterized apomictic Hieracium plants derived from D3 and A3.4 to assess conservation of the apomictic mechanism in different genetic backgrounds. The plants varied in ploidy, and also in the amount of DNA introduced from sexual Hieracium pilosella (P4). An apomictic hybrid from a cross between the two apomicts was also examined. The developmental processes observed in the parental apomicts were not conserved in the examined plants and alterations occurred in the components of Apomixis. One plant also exhibited adventitious embryony. The results show that other genetic factors can modify Apomixis with respect to time of initiation, spatial location, and mode of developmental progression. Both the apomictic locus and the modifiers are essential for efficient penetrance of the trait in Hieracium. Some of the findings in Hieracium correspond with observations in Ranunculus and this is discussed in terms of models for apomictic development and the control of Apomixis in crops.

Ueli Grossniklaus - One of the best experts on this subject based on the ideXlab platform.

  • The Boechera Genus as a Resource for Apomixis Research
    Frontiers Media S.A., 2019
    Co-Authors: Vladimir Brukhin, Jaroslaw V. Osadtchiy, Ana Marcela Florez-rueda, Dmitry Smetanin, Evgeny Bakin, Margarida Sofia Nobre, Ueli Grossniklaus
    Abstract:

    The genera Boechera (A. Löve et D. Löve) and Arabidopsis, the latter containing the model plant Arabidopsis thaliana, belong to the same clade within the Brassicaceae family. Boechera is the only among the more than 370 genera in the Brassicaceae where Apomixis is well documented. Apomixis refers to the asexual reproduction through seed, and a better understanding of the underlying mechanisms has great potential for applications in agriculture. The Boechera genus currently includes 110 species (of which 38 are reported to be triploid and thus apomictic), which are distributed mostly in the North America. The apomictic lineages of Boechera occur at both the diploid and triploid level and show signs of a hybridogenic origin, resulting in a modification of their chromosome structure, as reflected by alloploidy, aneuploidy, substitutions of homeologous chromosomes, and the presence of aberrant chromosomes. In this review, we discuss the advantages of the Boechera genus to study Apomixis, consider its modes of reproduction as well as the inheritance and possible mechanisms controlling Apomixis. We also consider population genetic aspects and a possible role of hybridization at the origin of Apomixis in Boechera. The molecular tools available to study Boechera, such as transformation techniques, laser capture microdissection, analysis of transcriptomes etc. are also discussed. We survey available genome assemblies of Boechera spp. and point out the challenges to assemble the highly heterozygous genomes of apomictic species. Due to these challenges, we argue for the application of an alternative reference-free method for the comparative analysis of such genomes, provide an overview of genomic sequencing data in the genus Boechera suitable for such analysis, and provide examples of its application

  • Apomictic and Sexual Germline Development Differ with Respect to Cell Cycle, Transcriptional, Hormonal and Epigenetic Regulation
    2016
    Co-Authors: Anja Schmidt, Marc W. Schmid, Ulrich C. Klostermeier, Christian Sailer, Manuel Waller, Philip Rosenstiel, Ueli Grossniklaus
    Abstract:

    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

  • apomictic and sexual germline development differ with respect to cell cycle transcriptional hormonal and epigenetic regulation
    PLOS Genetics, 2014
    Co-Authors: Anja Schmidt, Marc W. Schmid, Ulrich C. Klostermeier, Christian Sailer, Manuel Waller, Philip Rosenstiel, Weihong Qi, Daniela Guthorl, Ueli Grossniklaus
    Abstract:

    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.