Nico Storme - Academia.edu (original) (raw)

Papers by Nico Storme

Research paper thumbnail of Callose homeostasis at plasmodesmata: molecular regulators and developmental relevance

Frontiers in Plant Science, 2014

Plasmodesmata are membrane-lined channels that are located in the plant cell wall and that physic... more Plasmodesmata are membrane-lined channels that are located in the plant cell wall and that physically interconnect the cytoplasm and the endoplasmic reticulum (ER) of adjacent cells. Operating as controllable gates, plasmodesmata regulate the symplastic trafficking of micro-and macromolecules, such as endogenous proteins [transcription factors (TFs)] and RNA-based signals (mRNA, siRNA, etc.), hence mediating direct cell-to-cell communication and long distance signaling. Besides this physiological role, plasmodesmata also form gateways through which viral genomes can pass, largely facilitating the pernicious spread of viral infections. Plasmodesmatal trafficking is either passive (e.g., diffusion) or active and responses both to developmental and environmental stimuli. In general, plasmodesmatal conductivity is regulated by the controlled build-up of callose at the plasmodesmatal neck, largely mediated by the antagonistic action of callose synthases (CalSs) and β-1,3-glucanases. Here, in this theory and hypothesis paper, we outline the importance of callose metabolism in PD SEL control, and highlight the main molecular factors involved. In addition, we also review other proteins that regulate symplastic PD transport, both in a developmental and stress-responsive framework, and discuss on their putative role in the modulation of PD callose turn-over. Finally, we hypothesize on the role of structural sterols in the regulation of (PD) callose deposition and outline putative mechanisms by which this regulation may occur.

Research paper thumbnail of SGO1 but not SGO2 is required for maintenance of centromere cohesion in Arabidopsis thaliana meiosis

Plant reproduction, 2013

Shugoshin is a protein conserved in eukaryotes and protects sister chromatid cohesion at centrome... more Shugoshin is a protein conserved in eukaryotes and protects sister chromatid cohesion at centromeres in meiosis. In our study, we identified the homologs of SGO1 and SGO2 in Arabidopsis thaliana. We show that AtSGO1 is necessary for the maintenance of centromere cohesion in meiosis I since atsgo1 mutants display premature separation of sister chromatids starting from anaphase I. Furthermore, we show that the localization of the specific centromeric cohesin AtSYN1 is not affected in atsgo1, suggesting that SGO1 centromere cohesion maintenance is not mediated by protection of SYN1 from cleavage. Finally, we show that AtSGO2 is dispensable for both meiotic and mitotic cell progression in Arabidopsis.

Research paper thumbnail of Genes controlling the formation of unreduced pollen in Arabidopsis thaliana a forward genetics approach

Communications in agricultural and applied biological sciences, 2008

... Record Details. Record ID, 533865. Record Type, journalArticle. Author, Nico De Storme [80200... more ... Record Details. Record ID, 533865. Record Type, journalArticle. Author, Nico De Storme [802000083801] - Ghent University Nico.DeStorme@UGent.be; Marie-Christine Van Labeke [801001891456] - Ghent University MarieChristine.VanLabeke@UGent.be; ...

Research paper thumbnail of Formation of unreduced pollen in Arabidopsis thaliana

Communications in agricultural and applied biological sciences, 2007

Unreduced pollen can be formed by pre-or post-meiotic chromosome doubling (endo-reduplication), b... more Unreduced pollen can be formed by pre-or post-meiotic chromosome doubling (endo-reduplication), but are mainly the result of a meiotic disfunctionment, which leads to a mitosis-like non-reduced division. Although 2n pollen may result from a variety of different ...

Research paper thumbnail of Cell cycle-dependent O-GlcNAc modification of tobacco histones and their interaction with the tobacco lectin

Plant Physiology and Biochemistry, 2014

The Nicotiana tabacum agglutinin or Nictaba is a nucleocytoplasmic lectin that is expressed in to... more The Nicotiana tabacum agglutinin or Nictaba is a nucleocytoplasmic lectin that is expressed in tobacco after the plants have been exposed to jasmonate treatment or insect herbivory. Nictaba specifically recognizes GlcNAc residues. Recently, it was shown that Nictaba is interacting in vitro with the core histone proteins from calf thymus. Assuming that plant histones e similar to their animal counterparts e undergo O-GlcNAcylation, this interaction presumably occurs through binding of the lectin to the O-GlcNAc modification present on the histones. Hereupon, the question was raised whether this modification also occurs in plants and if it is cell cycle dependent. To this end, histones were purified from tobacco BY-2 suspension cells and the presence of O-GlcNAc modifications was checked. Concomitantly, O-GlcNAcylation of histone proteins was studied. Our data show that similar to animal histones plant histones are modified by O-GlcNAc in a cell cycle-dependent fashion. In addition, the interaction between Nictaba and tobacco histones was confirmed using lectin chromatography and far Western blot analysis. Collectively these findings suggest that Nictaba can act as a modulator of gene transcription through its interaction with core histones.

Research paper thumbnail of Sexual polyploidization in plants - cytological mechanisms and molecular regulation

Research paper thumbnail of Chromosome segregation in plant meiosis

Frontiers in Plant Science, 2014

Faithful chromosome segregation in meiosis is essential for ploidy stability over sexual life cyc... more Faithful chromosome segregation in meiosis is essential for ploidy stability over sexual life cycles. In plants, defective chromosome segregation caused by gene mutations or other factors leads to the formation of unbalanced or unreduced gametes creating aneuploid or polyploid progeny, respectively. Accurate segregation requires the coordinated execution of conserved processes occurring throughout the two meiotic cell divisions. Synapsis and recombination ensure the establishment of chiasmata that hold homologous chromosomes together allowing their correct segregation in the first meiotic division, which is also tightly regulated by cell-cycle dependent release of cohesin and monopolar attachment of sister kinetochores to microtubules. In meiosis II, bi-orientation of sister kinetochores and proper spindle orientation correctly segregate chromosomes in four haploid cells. Checkpoint mechanisms acting at kinetochores control the accuracy of kinetochore-microtubule attachment, thus ensuring the completion of segregation. Here we review the current knowledge on the processes taking place during chromosome segregation in plant meiosis, focusing on the characterization of the molecular factors involved.

Research paper thumbnail of Volume-based pollen size analysis: an advanced method to assess somatic and gametophytic ploidy in flowering plants

Plant Reproduction, 2013

Pollen size is often used as a biological parameter to estimate the ploidy and viability of matur... more Pollen size is often used as a biological parameter to estimate the ploidy and viability of mature pollen grains. In general, pollen size quantification is performed one-or two-dimensionally using image-based diameter measurements. As these approaches are elaborate and time consuming, alternative approaches that enable a quick, reliable analysis of pollen size are highly relevant for plant research. In this study, we present the volumebased particle size analysis technique as an alternative method to characterize mature pollen. Based on a comparative assay using different plant species (including tomato, oilseed rape, kiwifruit, clover, among others), we found that volume-based pollen size measurements are not biased by the pollen shape or position and substantially reduce non-biological variation, allowing a more accurate determination of the actual pollen size. As such, volumebased particle size techniques have a strong discriminative power in detecting pollen size differences caused by alterations in the gametophytic ploidy level and therefore allow for a quick and reliable estimation of the somatic ploidy level. Based on observations in Arabidopsis thaliana gametophytic mutants and differentially reproducing Boechera polyantha lines, we additionally found that volume-based pollen size analysis provides quantitative and qualitative data about alterations in male sporogenesis, including aneuploid and diploid gamete formation. Volume-based pollen size analysis therefore not only provides a quick and easy methodology to determine the somatic ploidy level of flowering plants, but can also be used to determine the mode of reproduction and to quantify the level of diplogamete formation.

Research paper thumbnail of Plant speciation through chromosome instability and ploidy change: Cellular mechanisms, molecular factors and evolutionary relevance

Current Plant Biology, 2014

Plant speciation and diversification strongly rely on structural changes in the nuclear genome, b... more Plant speciation and diversification strongly rely on structural changes in the nuclear genome, both at the whole ploidy and individual chromosome level. Phylogenetic, comparative mapping and cytological studies have provided insights into the evolutionary mechanisms that shape the plant genome. These include major genome alterations, such as whole genome duplication and hybridization (auto-and allopolyploidy), but also comprise the concomitant or independent occurrence of minor chromosome changes, such as aneuploidization and dysploidy (inversions and translocations). Despite the relevance of chromosomal instability as a driver for genome evolution and adaptation, little is yet known about the cellular mechanisms and processes that actually underlie these modifications. Here, in this paper, we provide a comprehensive overview of somatic and meiotic defects that lead to polyploidy or structural genome changes and discuss their relevance for plant genome evolution and speciation. In addition, we elaborate on the existence of stress-induced changes in chromosome and ploidy integrity in plants and their putative role in boosting adaptive genome evolution in hostile environments.

Research paper thumbnail of SHUGOSHINs and PATRONUS protect meiotic centromere cohesion in Arabidopsis thaliana

The Plant Journal, 2014

In meiosis, chromosome cohesion is maintained by the cohesin complex, which is released in a two-... more In meiosis, chromosome cohesion is maintained by the cohesin complex, which is released in a two-step manner. At meiosis I, the meiosis-specific cohesin subunit Rec8 is cleaved by the protease Separase along chromosome arms, allowing homologous chromosome segregation. Next, in meiosis II, cleavage of the remaining centromere cohesin results in separation of the sister chromatids. In eukaryotes, protection of centromeric cohesion in meiosis I is mediated by SHUGOSHINs (SGOs). The Arabidopsis genome contains two SGO homologs.

Research paper thumbnail of GLUCAN SYNTHASE-LIKE8 and STEROL METHYLTRANSFERASE2 Are Required for Ploidy Consistency of the Sexual Reproduction System in Arabidopsis

The Plant Cell, 2013

In sexually reproducing plants, the meiocyte-producing archesporal cell lineage is maintained at ... more In sexually reproducing plants, the meiocyte-producing archesporal cell lineage is maintained at the diploid state to consolidate the formation of haploid gametes. In search of molecular factors that regulate this ploidy consistency, we isolated an Arabidopsis thaliana mutant, called enlarged tetrad2 (et2), which produces tetraploid meiocytes through the stochastic occurrence of premeiotic endomitosis. Endomitotic polyploidization events were induced by alterations in cell wall formation, and similar cytokinetic defects were sporadically observed in other tissues, including cotyledons and leaves. ET2 encodes GLUCAN SYNTHASE-LIKE8 (GSL8), a callose synthase that mediates the deposition of callose at developing cell plates, root hairs, and plasmodesmata. Unlike other gsl8 mutants, in which defects in cell plate formation are seedling lethal, cytokinetic defects in et2 predominantly occur in flowers and have little effect on vegetative growth and development. Similarly, mutations in STEROL METHYLTRANSFERASE2 (SMT2), a major sterol biosynthesis enzyme, also lead to weak cytokinetic defects, primarily in the flowers. In addition, SMT2 allelic mutants also generate tetraploid meiocytes through the ectopic induction of premeiotic endomitosis. These observations demonstrate that appropriate callose and sterol biosynthesis are required for maintaining the ploidy level of the premeiotic germ lineage and that subtle defects in cytokinesis may lead to diploid gametes and polyploid offspring.

Research paper thumbnail of The impact of environmental stress on male reproductive development in plants: biological processes and molecular mechanisms

Plant, Cell & Environment, 2014

In plants, male reproductive development is extremely sensitive to adverse climatic environments ... more In plants, male reproductive development is extremely sensitive to adverse climatic environments and (a)biotic stress. Upon exposure to stress, male gametophytic organs often show morphological, structural and metabolic alterations that typically lead to meiotic defects or premature spore abortion and male reproductive sterility. Depending on the type of stress involved (e.g. heat, cold, drought) and the duration of stress exposure, the underlying cellular defect is highly variable and either involves cytoskeletal alterations, tapetal irregularities, altered sugar utilization, aberrations in auxin metabolism, accumulation of reactive oxygen species (ROS; oxidative stress) or the ectopic induction of programmed cell death (PCD). In this review, we present the critically stress-sensitive stages of male sporogenesis (meiosis) and male gametogenesis (microspore development), and discuss the corresponding biological processes involved and the resulting alterations in male reproduction. In addition, this review also provides insights into the molecular and/or hormonal regulation of the environmental stress sensitivity of male reproduction and outlines putative interaction(s) between the different processes involved.

Research paper thumbnail of Cytokinesis in plant male meiosis

Plant Signaling & Behavior, 2013

In mitotically dividing cells, separation of chromosomes (e.g., nuclear division) is followed by ... more In mitotically dividing cells, separation of chromosomes (e.g., nuclear division) is followed by a physical separation of the two daughter nuclei by the establishment of a cell plate and/or cell wall (e.g., cell division). This process is generally termed cytokinesis and is considered an essential part of the mitotic cell cycle, more specifically as the final step of the mitotic M-phase. Indeed, loss of cell plate formation in most organisms typically leads to severe defects in cell proliferation and cell differentiation, mostly causing a premature abortion of the tissue or organ involved. Based on the different cell structure and morphology of various biological systems (e.g., rigid cell wall in plants does not occur in animal cells), the process of cytokinesis shows a large variability between the different kingdoms, with a strong difference between plants and other eukaryotic organisms. 4,5 In animals and yeast, following nuclear division, cytokinesis is initiated at the periphery of the division plane with the specification of the cleavage plane and subsequent rearrangement of microtubule (MT) structures that form a structural basis for the formation of the actin-myosin-based contractile ring. 6-9 This actomyosin ring in somatic cell division, cytokinesis is the final step of the cell cycle and physically divides the mother cytoplasm into two daughter cells. in the meiotic cell division, however, pollen mother cells (PMCs) undergo two successive nuclear divisions without an intervening S-phase and consequently generate four haploid daughter nuclei out of one parental cell. in line with this, the physical separation of meiotic nuclei does not follow the conventional cytokinesis pathway, but instead is mediated by alternative processes, including polar-based phragmoplast outgrowth and rMA-mediated cell wall positioning. in this review, we outline the different cytological mechanisms of cell plate formation operating in different types of PMCs and additionally focus on some important features associated with male meiotic cytokinesis, including cytoskeletal dynamics and callose deposition. we also provide an up-to-date overview of the main molecular actors involved in PMC wall formation and additionally highlight some recent advances on the effect of cold stress on meiotic cytokinesis in plants.

Research paper thumbnail of Production of Diploid Male Gametes in Arabidopsis by Cold-Induced Destabilization of Postmeiotic Radial Microtubule Arrays

PLANT PHYSIOLOGY, 2012

Whole-genome duplication through the formation of diploid gametes is a major route for polyploidi... more Whole-genome duplication through the formation of diploid gametes is a major route for polyploidization, speciation, and diversification in plants. The prevalence of polyploids in adverse climates led us to hypothesize that abiotic stress conditions can induce or stimulate diploid gamete production. In this study, we show that short periods of cold stress induce the production of diploid and polyploid pollen in Arabidopsis (Arabidopsis thaliana). Using a combination of cytological and genetic analyses, we demonstrate that cold stress alters the formation of radial microtubule arrays at telophase II and consequently leads to defects in postmeiotic cytokinesis and cell wall formation. As a result, cold-stressed male meiosis generates triads, dyads, and monads that contain binuclear and polynuclear microspores. Fusion of nuclei in binuclear and polynuclear microspores occurs spontaneously before pollen mitosis I and eventually leads to the formation of diploid and polyploid pollen grains. Using segregation analyses, we also found that the majority of cold-induced dyads and triads are genetically equivalent to a second division restitution and produce diploid gametes that are highly homozygous. In a broader perspective, these findings offer insights into the fundamental mechanisms that regulate male gametogenesis in plants and demonstrate that their sensitivity to environmental stress has evolutionary significance and agronomic relevance in terms of polyploidization. Nick P (2003) Is microtubule disassembly a trigger for cold acclimation? Plant Cell Physiol 44: 676-686

Research paper thumbnail of Saponin production is not qualitatively changed upon callus regeneration in the medicinal shrub Maesa perlarius

Plant Growth Regulation, 2013

ABSTRACT Maesa perlarius is a medicinal plant that produces maesabalides, which possess selective... more ABSTRACT Maesa perlarius is a medicinal plant that produces maesabalides, which possess selective and strong anti-leishmania activity. In this study, M. perlarius plants were regenerated from leaf-derived calli. Shoots were induced in Murashige and Skoog medium in the presence of thidiazuron in combination with α-naphthalene acetic acid. In contrast to seed-derived plants, callus-derived regenerants were tetraploid showing typical characteristics of higher ploidy phenotypes. We assessed the impact of indirect plant regeneration and associated increase in ploidy on the production of saponin by means of LC–MS analysis. Tetraploid M. perlarius produce a saponin profile, which was not significantly different from seed grown plants. Based on this study, we concluded that saponin production in M. perlarius is not qualitatively changed by a genome-doubling event.

Research paper thumbnail of Pre-meiotic endomitosis in the cytokinesis-defective tomato mutant pmcd1 generates tetraploid meiocytes and diploid gametes

Journal of Experimental Botany, 2013

Sexual polyploidization through the formation and functioning of 2n gametes is considered a major... more Sexual polyploidization through the formation and functioning of 2n gametes is considered a major route for plant speciation and diversification. The cellular mechanism underlying 2n gamete formation mostly involves a restitution of the meiotic cell cycle, generating dyads and triads instead of tetrad meiotic end-products. As an alternative mechanism, the tomato mutant pmcd1 (for pre-meiotic cytokinesis defect 1), which generates diploid gametes through the ectopic induction of pre-meiotic endomitosis, is presented here. Using cytological approaches, it is demonstrated that male pmcd1 meiocyte initials exhibit clear alterations in cell cycle progression and cell plate formation, and consequently form syncytial cells that display different grades of cellular and/or nuclear fusion. In addition, it was found that other somatic tissue types (e.g. cotyledons and petals) also display occasional defects in cell wall formation and exhibit alterations in callose deposition, indicating that pmcd1 has a general defect in cell plate formation, most probably caused by alterations in callose biosynthesis. In a broader perspective, these findings demonstrate that defects in cytokinesis and cell plate formation may constitute a putative route for diplogamete formation and sexual polyploidization in plants.

Research paper thumbnail of Sporophytic and gametophytic functions of the cell cycle-associated Mob1 gene in Arabidopsis thaliana L

Gene, 2011

Mob1 genes are primarily involved in the cell cycle progression and mitosis exit in yeasts and an... more Mob1 genes are primarily involved in the cell cycle progression and mitosis exit in yeasts and animals. The function of a Mob1-like gene (At5g45550) from Arabidopsis thaliana was investigated using RNAi and immunological staining. AtMob1-like RNAi silenced lines showed a reduced radial expansion of the inflorescence stem and a reduced elongation zone of the primary root. Morphological features of plant organs were accompanied by a reduction in cell size. The fertility of AtMob1-like RNAi silenced lines was very low as seed production was strongly reduced. About 2% of the progeny of AtMob1-like RNAi silenced plants were tetraploid. The female and male sporogenesis was affected differentially. The ovules developed irregularly and one third of the megaspores and embryo sacs degenerated prematurely. Up to 20% of the ovules produced binucleated megaspores that failed to develop further, being their degeneration likely accompanied with a delayed programmed cell death. The anthers produced about 30% of aborted pollen grains, showing also a strong variation in their size. Together, the results show that Arabidopsis MOB1-like is required to regulate cell expansion and cell division, presumably by affecting the mitotic as well as the meiotic cell cycle.

Research paper thumbnail of Altered expression of Aurora kinases in Arabidopsis results in aneu- and polyploidization

Research paper thumbnail of Callose homeostasis at plasmodesmata: molecular regulators and developmental relevance

Frontiers in Plant Science, 2014

Plasmodesmata are membrane-lined channels that are located in the plant cell wall and that physic... more Plasmodesmata are membrane-lined channels that are located in the plant cell wall and that physically interconnect the cytoplasm and the endoplasmic reticulum (ER) of adjacent cells. Operating as controllable gates, plasmodesmata regulate the symplastic trafficking of micro-and macromolecules, such as endogenous proteins [transcription factors (TFs)] and RNA-based signals (mRNA, siRNA, etc.), hence mediating direct cell-to-cell communication and long distance signaling. Besides this physiological role, plasmodesmata also form gateways through which viral genomes can pass, largely facilitating the pernicious spread of viral infections. Plasmodesmatal trafficking is either passive (e.g., diffusion) or active and responses both to developmental and environmental stimuli. In general, plasmodesmatal conductivity is regulated by the controlled build-up of callose at the plasmodesmatal neck, largely mediated by the antagonistic action of callose synthases (CalSs) and β-1,3-glucanases. Here, in this theory and hypothesis paper, we outline the importance of callose metabolism in PD SEL control, and highlight the main molecular factors involved. In addition, we also review other proteins that regulate symplastic PD transport, both in a developmental and stress-responsive framework, and discuss on their putative role in the modulation of PD callose turn-over. Finally, we hypothesize on the role of structural sterols in the regulation of (PD) callose deposition and outline putative mechanisms by which this regulation may occur.

Research paper thumbnail of SGO1 but not SGO2 is required for maintenance of centromere cohesion in Arabidopsis thaliana meiosis

Plant reproduction, 2013

Shugoshin is a protein conserved in eukaryotes and protects sister chromatid cohesion at centrome... more Shugoshin is a protein conserved in eukaryotes and protects sister chromatid cohesion at centromeres in meiosis. In our study, we identified the homologs of SGO1 and SGO2 in Arabidopsis thaliana. We show that AtSGO1 is necessary for the maintenance of centromere cohesion in meiosis I since atsgo1 mutants display premature separation of sister chromatids starting from anaphase I. Furthermore, we show that the localization of the specific centromeric cohesin AtSYN1 is not affected in atsgo1, suggesting that SGO1 centromere cohesion maintenance is not mediated by protection of SYN1 from cleavage. Finally, we show that AtSGO2 is dispensable for both meiotic and mitotic cell progression in Arabidopsis.

Research paper thumbnail of Genes controlling the formation of unreduced pollen in Arabidopsis thaliana a forward genetics approach

Communications in agricultural and applied biological sciences, 2008

... Record Details. Record ID, 533865. Record Type, journalArticle. Author, Nico De Storme [80200... more ... Record Details. Record ID, 533865. Record Type, journalArticle. Author, Nico De Storme [802000083801] - Ghent University Nico.DeStorme@UGent.be; Marie-Christine Van Labeke [801001891456] - Ghent University MarieChristine.VanLabeke@UGent.be; ...

Research paper thumbnail of Formation of unreduced pollen in Arabidopsis thaliana

Communications in agricultural and applied biological sciences, 2007

Unreduced pollen can be formed by pre-or post-meiotic chromosome doubling (endo-reduplication), b... more Unreduced pollen can be formed by pre-or post-meiotic chromosome doubling (endo-reduplication), but are mainly the result of a meiotic disfunctionment, which leads to a mitosis-like non-reduced division. Although 2n pollen may result from a variety of different ...

Research paper thumbnail of Cell cycle-dependent O-GlcNAc modification of tobacco histones and their interaction with the tobacco lectin

Plant Physiology and Biochemistry, 2014

The Nicotiana tabacum agglutinin or Nictaba is a nucleocytoplasmic lectin that is expressed in to... more The Nicotiana tabacum agglutinin or Nictaba is a nucleocytoplasmic lectin that is expressed in tobacco after the plants have been exposed to jasmonate treatment or insect herbivory. Nictaba specifically recognizes GlcNAc residues. Recently, it was shown that Nictaba is interacting in vitro with the core histone proteins from calf thymus. Assuming that plant histones e similar to their animal counterparts e undergo O-GlcNAcylation, this interaction presumably occurs through binding of the lectin to the O-GlcNAc modification present on the histones. Hereupon, the question was raised whether this modification also occurs in plants and if it is cell cycle dependent. To this end, histones were purified from tobacco BY-2 suspension cells and the presence of O-GlcNAc modifications was checked. Concomitantly, O-GlcNAcylation of histone proteins was studied. Our data show that similar to animal histones plant histones are modified by O-GlcNAc in a cell cycle-dependent fashion. In addition, the interaction between Nictaba and tobacco histones was confirmed using lectin chromatography and far Western blot analysis. Collectively these findings suggest that Nictaba can act as a modulator of gene transcription through its interaction with core histones.

Research paper thumbnail of Sexual polyploidization in plants - cytological mechanisms and molecular regulation

Research paper thumbnail of Chromosome segregation in plant meiosis

Frontiers in Plant Science, 2014

Faithful chromosome segregation in meiosis is essential for ploidy stability over sexual life cyc... more Faithful chromosome segregation in meiosis is essential for ploidy stability over sexual life cycles. In plants, defective chromosome segregation caused by gene mutations or other factors leads to the formation of unbalanced or unreduced gametes creating aneuploid or polyploid progeny, respectively. Accurate segregation requires the coordinated execution of conserved processes occurring throughout the two meiotic cell divisions. Synapsis and recombination ensure the establishment of chiasmata that hold homologous chromosomes together allowing their correct segregation in the first meiotic division, which is also tightly regulated by cell-cycle dependent release of cohesin and monopolar attachment of sister kinetochores to microtubules. In meiosis II, bi-orientation of sister kinetochores and proper spindle orientation correctly segregate chromosomes in four haploid cells. Checkpoint mechanisms acting at kinetochores control the accuracy of kinetochore-microtubule attachment, thus ensuring the completion of segregation. Here we review the current knowledge on the processes taking place during chromosome segregation in plant meiosis, focusing on the characterization of the molecular factors involved.

Research paper thumbnail of Volume-based pollen size analysis: an advanced method to assess somatic and gametophytic ploidy in flowering plants

Plant Reproduction, 2013

Pollen size is often used as a biological parameter to estimate the ploidy and viability of matur... more Pollen size is often used as a biological parameter to estimate the ploidy and viability of mature pollen grains. In general, pollen size quantification is performed one-or two-dimensionally using image-based diameter measurements. As these approaches are elaborate and time consuming, alternative approaches that enable a quick, reliable analysis of pollen size are highly relevant for plant research. In this study, we present the volumebased particle size analysis technique as an alternative method to characterize mature pollen. Based on a comparative assay using different plant species (including tomato, oilseed rape, kiwifruit, clover, among others), we found that volume-based pollen size measurements are not biased by the pollen shape or position and substantially reduce non-biological variation, allowing a more accurate determination of the actual pollen size. As such, volumebased particle size techniques have a strong discriminative power in detecting pollen size differences caused by alterations in the gametophytic ploidy level and therefore allow for a quick and reliable estimation of the somatic ploidy level. Based on observations in Arabidopsis thaliana gametophytic mutants and differentially reproducing Boechera polyantha lines, we additionally found that volume-based pollen size analysis provides quantitative and qualitative data about alterations in male sporogenesis, including aneuploid and diploid gamete formation. Volume-based pollen size analysis therefore not only provides a quick and easy methodology to determine the somatic ploidy level of flowering plants, but can also be used to determine the mode of reproduction and to quantify the level of diplogamete formation.

Research paper thumbnail of Plant speciation through chromosome instability and ploidy change: Cellular mechanisms, molecular factors and evolutionary relevance

Current Plant Biology, 2014

Plant speciation and diversification strongly rely on structural changes in the nuclear genome, b... more Plant speciation and diversification strongly rely on structural changes in the nuclear genome, both at the whole ploidy and individual chromosome level. Phylogenetic, comparative mapping and cytological studies have provided insights into the evolutionary mechanisms that shape the plant genome. These include major genome alterations, such as whole genome duplication and hybridization (auto-and allopolyploidy), but also comprise the concomitant or independent occurrence of minor chromosome changes, such as aneuploidization and dysploidy (inversions and translocations). Despite the relevance of chromosomal instability as a driver for genome evolution and adaptation, little is yet known about the cellular mechanisms and processes that actually underlie these modifications. Here, in this paper, we provide a comprehensive overview of somatic and meiotic defects that lead to polyploidy or structural genome changes and discuss their relevance for plant genome evolution and speciation. In addition, we elaborate on the existence of stress-induced changes in chromosome and ploidy integrity in plants and their putative role in boosting adaptive genome evolution in hostile environments.

Research paper thumbnail of SHUGOSHINs and PATRONUS protect meiotic centromere cohesion in Arabidopsis thaliana

The Plant Journal, 2014

In meiosis, chromosome cohesion is maintained by the cohesin complex, which is released in a two-... more In meiosis, chromosome cohesion is maintained by the cohesin complex, which is released in a two-step manner. At meiosis I, the meiosis-specific cohesin subunit Rec8 is cleaved by the protease Separase along chromosome arms, allowing homologous chromosome segregation. Next, in meiosis II, cleavage of the remaining centromere cohesin results in separation of the sister chromatids. In eukaryotes, protection of centromeric cohesion in meiosis I is mediated by SHUGOSHINs (SGOs). The Arabidopsis genome contains two SGO homologs.

Research paper thumbnail of GLUCAN SYNTHASE-LIKE8 and STEROL METHYLTRANSFERASE2 Are Required for Ploidy Consistency of the Sexual Reproduction System in Arabidopsis

The Plant Cell, 2013

In sexually reproducing plants, the meiocyte-producing archesporal cell lineage is maintained at ... more In sexually reproducing plants, the meiocyte-producing archesporal cell lineage is maintained at the diploid state to consolidate the formation of haploid gametes. In search of molecular factors that regulate this ploidy consistency, we isolated an Arabidopsis thaliana mutant, called enlarged tetrad2 (et2), which produces tetraploid meiocytes through the stochastic occurrence of premeiotic endomitosis. Endomitotic polyploidization events were induced by alterations in cell wall formation, and similar cytokinetic defects were sporadically observed in other tissues, including cotyledons and leaves. ET2 encodes GLUCAN SYNTHASE-LIKE8 (GSL8), a callose synthase that mediates the deposition of callose at developing cell plates, root hairs, and plasmodesmata. Unlike other gsl8 mutants, in which defects in cell plate formation are seedling lethal, cytokinetic defects in et2 predominantly occur in flowers and have little effect on vegetative growth and development. Similarly, mutations in STEROL METHYLTRANSFERASE2 (SMT2), a major sterol biosynthesis enzyme, also lead to weak cytokinetic defects, primarily in the flowers. In addition, SMT2 allelic mutants also generate tetraploid meiocytes through the ectopic induction of premeiotic endomitosis. These observations demonstrate that appropriate callose and sterol biosynthesis are required for maintaining the ploidy level of the premeiotic germ lineage and that subtle defects in cytokinesis may lead to diploid gametes and polyploid offspring.

Research paper thumbnail of The impact of environmental stress on male reproductive development in plants: biological processes and molecular mechanisms

Plant, Cell & Environment, 2014

In plants, male reproductive development is extremely sensitive to adverse climatic environments ... more In plants, male reproductive development is extremely sensitive to adverse climatic environments and (a)biotic stress. Upon exposure to stress, male gametophytic organs often show morphological, structural and metabolic alterations that typically lead to meiotic defects or premature spore abortion and male reproductive sterility. Depending on the type of stress involved (e.g. heat, cold, drought) and the duration of stress exposure, the underlying cellular defect is highly variable and either involves cytoskeletal alterations, tapetal irregularities, altered sugar utilization, aberrations in auxin metabolism, accumulation of reactive oxygen species (ROS; oxidative stress) or the ectopic induction of programmed cell death (PCD). In this review, we present the critically stress-sensitive stages of male sporogenesis (meiosis) and male gametogenesis (microspore development), and discuss the corresponding biological processes involved and the resulting alterations in male reproduction. In addition, this review also provides insights into the molecular and/or hormonal regulation of the environmental stress sensitivity of male reproduction and outlines putative interaction(s) between the different processes involved.

Research paper thumbnail of Cytokinesis in plant male meiosis

Plant Signaling & Behavior, 2013

In mitotically dividing cells, separation of chromosomes (e.g., nuclear division) is followed by ... more In mitotically dividing cells, separation of chromosomes (e.g., nuclear division) is followed by a physical separation of the two daughter nuclei by the establishment of a cell plate and/or cell wall (e.g., cell division). This process is generally termed cytokinesis and is considered an essential part of the mitotic cell cycle, more specifically as the final step of the mitotic M-phase. Indeed, loss of cell plate formation in most organisms typically leads to severe defects in cell proliferation and cell differentiation, mostly causing a premature abortion of the tissue or organ involved. Based on the different cell structure and morphology of various biological systems (e.g., rigid cell wall in plants does not occur in animal cells), the process of cytokinesis shows a large variability between the different kingdoms, with a strong difference between plants and other eukaryotic organisms. 4,5 In animals and yeast, following nuclear division, cytokinesis is initiated at the periphery of the division plane with the specification of the cleavage plane and subsequent rearrangement of microtubule (MT) structures that form a structural basis for the formation of the actin-myosin-based contractile ring. 6-9 This actomyosin ring in somatic cell division, cytokinesis is the final step of the cell cycle and physically divides the mother cytoplasm into two daughter cells. in the meiotic cell division, however, pollen mother cells (PMCs) undergo two successive nuclear divisions without an intervening S-phase and consequently generate four haploid daughter nuclei out of one parental cell. in line with this, the physical separation of meiotic nuclei does not follow the conventional cytokinesis pathway, but instead is mediated by alternative processes, including polar-based phragmoplast outgrowth and rMA-mediated cell wall positioning. in this review, we outline the different cytological mechanisms of cell plate formation operating in different types of PMCs and additionally focus on some important features associated with male meiotic cytokinesis, including cytoskeletal dynamics and callose deposition. we also provide an up-to-date overview of the main molecular actors involved in PMC wall formation and additionally highlight some recent advances on the effect of cold stress on meiotic cytokinesis in plants.

Research paper thumbnail of Production of Diploid Male Gametes in Arabidopsis by Cold-Induced Destabilization of Postmeiotic Radial Microtubule Arrays

PLANT PHYSIOLOGY, 2012

Whole-genome duplication through the formation of diploid gametes is a major route for polyploidi... more Whole-genome duplication through the formation of diploid gametes is a major route for polyploidization, speciation, and diversification in plants. The prevalence of polyploids in adverse climates led us to hypothesize that abiotic stress conditions can induce or stimulate diploid gamete production. In this study, we show that short periods of cold stress induce the production of diploid and polyploid pollen in Arabidopsis (Arabidopsis thaliana). Using a combination of cytological and genetic analyses, we demonstrate that cold stress alters the formation of radial microtubule arrays at telophase II and consequently leads to defects in postmeiotic cytokinesis and cell wall formation. As a result, cold-stressed male meiosis generates triads, dyads, and monads that contain binuclear and polynuclear microspores. Fusion of nuclei in binuclear and polynuclear microspores occurs spontaneously before pollen mitosis I and eventually leads to the formation of diploid and polyploid pollen grains. Using segregation analyses, we also found that the majority of cold-induced dyads and triads are genetically equivalent to a second division restitution and produce diploid gametes that are highly homozygous. In a broader perspective, these findings offer insights into the fundamental mechanisms that regulate male gametogenesis in plants and demonstrate that their sensitivity to environmental stress has evolutionary significance and agronomic relevance in terms of polyploidization. Nick P (2003) Is microtubule disassembly a trigger for cold acclimation? Plant Cell Physiol 44: 676-686

Research paper thumbnail of Saponin production is not qualitatively changed upon callus regeneration in the medicinal shrub Maesa perlarius

Plant Growth Regulation, 2013

ABSTRACT Maesa perlarius is a medicinal plant that produces maesabalides, which possess selective... more ABSTRACT Maesa perlarius is a medicinal plant that produces maesabalides, which possess selective and strong anti-leishmania activity. In this study, M. perlarius plants were regenerated from leaf-derived calli. Shoots were induced in Murashige and Skoog medium in the presence of thidiazuron in combination with α-naphthalene acetic acid. In contrast to seed-derived plants, callus-derived regenerants were tetraploid showing typical characteristics of higher ploidy phenotypes. We assessed the impact of indirect plant regeneration and associated increase in ploidy on the production of saponin by means of LC–MS analysis. Tetraploid M. perlarius produce a saponin profile, which was not significantly different from seed grown plants. Based on this study, we concluded that saponin production in M. perlarius is not qualitatively changed by a genome-doubling event.

Research paper thumbnail of Pre-meiotic endomitosis in the cytokinesis-defective tomato mutant pmcd1 generates tetraploid meiocytes and diploid gametes

Journal of Experimental Botany, 2013

Sexual polyploidization through the formation and functioning of 2n gametes is considered a major... more Sexual polyploidization through the formation and functioning of 2n gametes is considered a major route for plant speciation and diversification. The cellular mechanism underlying 2n gamete formation mostly involves a restitution of the meiotic cell cycle, generating dyads and triads instead of tetrad meiotic end-products. As an alternative mechanism, the tomato mutant pmcd1 (for pre-meiotic cytokinesis defect 1), which generates diploid gametes through the ectopic induction of pre-meiotic endomitosis, is presented here. Using cytological approaches, it is demonstrated that male pmcd1 meiocyte initials exhibit clear alterations in cell cycle progression and cell plate formation, and consequently form syncytial cells that display different grades of cellular and/or nuclear fusion. In addition, it was found that other somatic tissue types (e.g. cotyledons and petals) also display occasional defects in cell wall formation and exhibit alterations in callose deposition, indicating that pmcd1 has a general defect in cell plate formation, most probably caused by alterations in callose biosynthesis. In a broader perspective, these findings demonstrate that defects in cytokinesis and cell plate formation may constitute a putative route for diplogamete formation and sexual polyploidization in plants.

Research paper thumbnail of Sporophytic and gametophytic functions of the cell cycle-associated Mob1 gene in Arabidopsis thaliana L

Gene, 2011

Mob1 genes are primarily involved in the cell cycle progression and mitosis exit in yeasts and an... more Mob1 genes are primarily involved in the cell cycle progression and mitosis exit in yeasts and animals. The function of a Mob1-like gene (At5g45550) from Arabidopsis thaliana was investigated using RNAi and immunological staining. AtMob1-like RNAi silenced lines showed a reduced radial expansion of the inflorescence stem and a reduced elongation zone of the primary root. Morphological features of plant organs were accompanied by a reduction in cell size. The fertility of AtMob1-like RNAi silenced lines was very low as seed production was strongly reduced. About 2% of the progeny of AtMob1-like RNAi silenced plants were tetraploid. The female and male sporogenesis was affected differentially. The ovules developed irregularly and one third of the megaspores and embryo sacs degenerated prematurely. Up to 20% of the ovules produced binucleated megaspores that failed to develop further, being their degeneration likely accompanied with a delayed programmed cell death. The anthers produced about 30% of aborted pollen grains, showing also a strong variation in their size. Together, the results show that Arabidopsis MOB1-like is required to regulate cell expansion and cell division, presumably by affecting the mitotic as well as the meiotic cell cycle.

Research paper thumbnail of Altered expression of Aurora kinases in Arabidopsis results in aneu- and polyploidization