Publications by authors named "Pawel Roszak"

14 Publications

  • Page 1 of 1

Molecular mechanism of cytokinin-activated cell division in .

Science 2021 03 25;371(6536):1350-1355. Epub 2021 Feb 25.

Sainsbury Laboratory, University of Cambridge, Bateman Street, Cambridge CB2 1LR, UK.

Mitogens trigger cell division in animals. In plants, cytokinins, a group of phytohormones derived from adenine, stimulate cell proliferation. Cytokinin signaling is initiated by membrane-associated histidine kinase receptors and transduced through a phosphorelay system. We show that in the shoot apical meristem (SAM), cytokinin regulates cell division by promoting nuclear shuttling of Myb-domain protein 3R4 (MYB3R4), a transcription factor that activates mitotic gene expression. Newly synthesized MYB3R4 protein resides predominantly in the cytoplasm. At the G2-to-M transition, rapid nuclear accumulation of MYB3R4-consistent with an associated transient peak in cytokinin concentration-feeds a positive feedback loop involving importins and initiates a transcriptional cascade that drives mitosis and cytokinesis. An engineered nuclear-restricted MYB3R4 mimics the cytokinin effects of enhanced cell proliferation and meristem growth.
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http://dx.doi.org/10.1126/science.abe2305DOI Listing
March 2021

Specification and regulation of vascular tissue identity in the embryo.

Development 2020 04 20;147(8). Epub 2020 Apr 20.

Laboratory of Biochemistry, Wageningen University, Stippeneng 4, Wageningen, 6708WE, The Netherlands

Development of plant vascular tissues involves tissue identity specification, growth, pattern formation and cell-type differentiation. Although later developmental steps are understood in some detail, it is still largely unknown how the tissue is initially specified. We used the early embryo as a simple model to study this process. Using a large collection of marker genes, we found that vascular identity was specified in the 16-cell embryo. After a transient precursor state, however, there was no persistent uniform tissue identity. Auxin is intimately connected to vascular tissue development. We found that, although an AUXIN RESPONSE FACTOR5/MONOPTEROS (ARF5/MP)-dependent auxin response was required, it was not sufficient for tissue specification. We therefore used a large-scale enhanced yeast one-hybrid assay to identify potential regulators of vascular identity. Network and functional analysis of candidate regulators suggest that vascular identity is under robust, complex control. We found that one candidate regulator, the G-class bZIP transcription factor GBF2, can modulate vascular gene expression by tuning MP output through direct interaction. Our work uncovers components of a gene regulatory network that controls the initial specification of vascular tissue identity.
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http://dx.doi.org/10.1242/dev.186130DOI Listing
April 2020

DOF2.1 Controls Cytokinin-Dependent Vascular Cell Proliferation Downstream of TMO5/LHW.

Curr Biol 2019 02 24;29(3):520-529.e6. Epub 2019 Jan 24.

Ghent University, Department of Plant Biotechnology and Bioinformatics, Technologiepark 71, 9052 Ghent, Belgium; VIB Center for Plant Systems Biology, Technologiepark 71, 9052 Ghent, Belgium; Wageningen University, Laboratory of Biochemistry, Stippeneng 4, 6708 WE Wageningen, the Netherlands. Electronic address:

To create a three-dimensional structure, plants rely on oriented cell divisions and cell elongation. Oriented cell divisions are specifically important in procambium cells of the root to establish the different vascular cell types [1, 2]. These divisions are in part controlled by the auxin-controlled TARGET OF MONOPTEROS5 (TMO5) and LONESOME HIGHWAY (LHW) transcription factor complex [3-7]. Loss-of-function of tmo5 or lhw clade members results in strongly reduced vascular cell file numbers, whereas ectopic expression of both TMO5 and LHW can ubiquitously induce periclinal and radial cell divisions in all cell types of the root meristem. TMO5 and LHW interact only in young xylem cells, where they promote expression of two direct target genes involved in the final step of cytokinin (CK) biosynthesis, LONELY GUY3 (LOG3) and LOG4 [8, 9] Therefore, CK was hypothesized to act as a mobile signal from the xylem to trigger divisions in the neighboring procambium cells [3, 6]. To unravel how TMO5/LHW-dependent cytokinin regulates cell proliferation, we analyzed the transcriptional responses upon simultaneous induction of both transcription factors. Using inferred network analysis, we identified AT2G28510/DOF2.1 as a cytokinin-dependent downstream target gene. We further showed that DOF2.1 controls specific procambium cell divisions without inducing other cytokinin-dependent effects such as the inhibition of vascular differentiation. In summary, our results suggest that DOF2.1 and its closest homologs control vascular cell proliferation, thus leading to radial expansion of the root.
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http://dx.doi.org/10.1016/j.cub.2018.12.041DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6370950PMC
February 2019

Mobile PEAR transcription factors integrate positional cues to prime cambial growth.

Nature 2019 01 9;565(7740):490-494. Epub 2019 Jan 9.

Institute of Biotechnology, HiLIFE/Organismal and Evolutionary Biology Research Programme, Faculty of Biological and Environmental Sciences, Viikki Plant Science Centre, University of Helsinki, Helsinki, Finland.

Apical growth in plants initiates upon seed germination, whereas radial growth is primed only during early ontogenesis in procambium cells and activated later by the vascular cambium. Although it is not known how radial growth is organized and regulated in plants, this system resembles the developmental competence observed in some animal systems, in which pre-existing patterns of developmental potential are established early on. Here we show that in Arabidopsis the initiation of radial growth occurs around early protophloem-sieve-element cell files of the root procambial tissue. In this domain, cytokinin signalling promotes the expression of a pair of mobile transcription factors-PHLOEM EARLY DOF 1 (PEAR1) and PHLOEM EARLY DOF 2 (PEAR2)-and their four homologues (DOF6, TMO6, OBP2 and HCA2), which we collectively name PEAR proteins. The PEAR proteins form a short-range concentration gradient that peaks at protophloem sieve elements, and activates gene expression that promotes radial growth. The expression and function of PEAR proteins are antagonized by the HD-ZIP III proteins, well-known polarity transcription factors-the expression of which is concentrated in the more-internal domain of radially non-dividing procambial cells by the function of auxin, and mobile miR165 and miR166 microRNAs. The PEAR proteins locally promote transcription of their inhibitory HD-ZIP III genes, and thereby establish a negative-feedback loop that forms a robust boundary that demarks the zone of cell division. Taken together, our data establish that during root procambial development there exists a network in which a module that links PEAR and HD-ZIP III transcription factors integrates spatial information of the hormonal domains and miRNA gradients to provide adjacent zones of dividing and more-quiescent cells, which forms a foundation for further radial growth.
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http://dx.doi.org/10.1038/s41586-018-0839-yDOI Listing
January 2019

High levels of auxin signalling define the stem-cell organizer of the vascular cambium.

Nature 2019 01 9;565(7740):485-489. Epub 2019 Jan 9.

Institute of Biotechnology, HiLIFE, University of Helsinki, Helsinki, Finland.

Wood, a type of xylem tissue, originates from cell proliferation of the vascular cambium. Xylem is produced inside, and phloem outside, of the cambium. Morphogenesis in plants is typically coordinated by organizer cells that direct the adjacent stem cells to undergo programmed cell division and differentiation. The location of the vascular cambium stem cells and whether the organizer concept applies to the cambium are currently unknown. Here, using lineage-tracing and molecular genetic studies in the roots of Arabidopsis thaliana, we show that cells with a xylem identity direct adjacent vascular cambial cells to divide and function as stem cells. Thus, these xylem-identity cells constitute an organizer. A local maximum of the phytohormone auxin, and consequent expression of CLASS III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) transcription factors, promotes xylem identity and cellular quiescence of the organizer cells. Additionally, the organizer maintains phloem identity in a non-cell-autonomous fashion. Consistent with this dual function of the organizer cells, xylem and phloem originate from a single, bifacial stem cell in each radial cell file, which confirms the classical theory of a uniseriate vascular cambium. Clones that display high levels of ectopically activated auxin signalling differentiate as xylem vessels; these clones induce cell divisions and the expression of cambial and phloem markers in the adjacent cells, which suggests that a local auxin-signalling maximum is sufficient to specify a stem-cell organizer. Although vascular cambium has a unique function among plant meristems, the stem-cell organizer of this tissue shares features with the organizers of root and shoot meristems.
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http://dx.doi.org/10.1038/s41586-018-0837-0DOI Listing
January 2019

Arabidopsis SWC4 Binds DNA and Recruits the SWR1 Complex to Modulate Histone H2A.Z Deposition at Key Regulatory Genes.

Mol Plant 2018 06 29;11(6):815-832. Epub 2018 Mar 29.

Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM) - Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Campus Montegancedo UPM, Pozuelo de Alarcón, 28223 Madrid, Spain. Electronic address:

Deposition of the H2A.Z histone variant by the SWR1 complex (SWR1-C) in regulatory regions of specific loci modulates transcription. Characterization of mutations in Arabidopsis thaliana homologs of yeast SWR1-C has revealed a role for H2A.Z exchange in a variety of developmental processes. Nevertheless, the exact composition of plant SWR1-C and how it is recruited to target genes remains to be established. Here we show that SWC4, the Arabidopsis homolog of yeast SANT domain protein Swc4/Eaf2, is a DNA-binding protein that interacts with SWR1-C subunits. We demonstrate that the swc4-1 knockout mutant is embryo-lethal, while SWC4 RNAi knockdown lines display pleiotropic phenotypic alterations in vegetative and reproductive traits, including acceleration of flowering time, indicating that SWC4 controls post-embryonic processes. Transcriptomic analyses and genome-wide profiling of H2A.Z indicate that SWC4 represses transcription of a number of genes, including the floral integrator FT and key transcription factors, mainly by modulating H2A.Z deposition. Interestingly, SWC4 silencing does not affect H2A.Z deposition at the FLC locus nor expression of this gene, a master regulator of flowering previously shown to be controlled by SWR1-C. Importantly, we find that SWC4 recognizes specific AT-rich DNA elements in the chromatin regions of target genes and that SWC4 silencing impairs SWR1-C binding at FT. Collectively, our data suggest that SWC4 regulates plant growth and development by aiding SWR1-C recruitment and modulating H2A.Z deposition.
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http://dx.doi.org/10.1016/j.molp.2018.03.014DOI Listing
June 2018

Transgenerational phenotype aggravation in CAF-1 mutants reveals parent-of-origin specific epigenetic inheritance.

New Phytol 2018 11 24;220(3):908-921. Epub 2018 Mar 24.

Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, SE-75007, Uppsala, Sweden.

Chromatin is assembled by histone chaperones such as chromatin assembly factor CAF-1. We had noticed that vigor of Arabidopsis thaliana CAF-1 mutants decreased over several generations. Because changes in mutant phenotype severity over generations are unusual, we asked how repeated selfing of Arabidopsis CAF-1 mutants affects phenotype severity. CAF-1 mutant plants of various generations were grown, and developmental phenotypes, transcriptomes and DNA cytosine-methylation profiles were compared quantitatively. Shoot- and root-related growth phenotypes were progressively more affected in successive generations of CAF-1 mutants. Early and late generations of the fasciata (fas)2-4 CAF-1 mutant displayed only limited changes in gene expression, of which increasing upregulation of plant defense-related genes reflects the transgenerational phenotype aggravation. Likewise, global DNA methylation in the sequence context CHG but not CG or CHH (where H = A, T or C) changed over generations in fas2-4. Crossing early and late generation fas2-4 plants established that the maternal contribution to the phenotype severity exceeds the paternal contribution. Together, epigenetic rather than genetic mechanisms underlie the progressive developmental phenotype aggravation in the Arabidopsis CAF-1 mutants and preferred maternal transmission reveals a more efficient reprogramming of epigenetic information in the male than the female germline.
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http://dx.doi.org/10.1111/nph.15082DOI Listing
November 2018

Auxin production in the endosperm drives seed coat development in .

Elife 2016 11 16;5. Epub 2016 Nov 16.

Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala, Sweden.

In flowering plants, seed development is initiated by the fusion of the maternal egg and central cells with two paternal sperm cells, leading to the formation of embryo and endosperm, respectively. The fertilization products are surrounded by the maternally derived seed coat, whose development prior to fertilization is blocked by epigenetic regulators belonging to the Polycomb Group (PcG) protein family. Here we show that fertilization of the central cell results in the production of auxin and most likely its export to the maternal tissues, which drives seed coat development by removing PcG function. We furthermore show that mutants for the MADS-box transcription factor AGL62 have an impaired transport of auxin from the endosperm to the integuments, which results in seed abortion. We propose that AGL62 regulates auxin transport from the endosperm to the integuments, leading to the removal of the PcG block on seed coat development.
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http://dx.doi.org/10.7554/eLife.20542DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5135394PMC
November 2016

Auxin production couples endosperm development to fertilization.

Nat Plants 2015 Nov 23;1:15184. Epub 2015 Nov 23.

Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center of Plant Biology, Uppsala, Sweden.

In flowering plants, seed development is preceded by a double fertilization event, whereby two male sperm cells fuse with two female gametes: the egg and central cells. The fertilized egg cell will form the embryo, and the fertilized central cell will give rise to the triploid endosperm, whose function is to nourish and support the embryo. Even though the endosperm has an unparalleled role for human nutrition, the molecular bases for its development are yet to be understood. Our results reveal that increasing auxin levels after fertilization drive the replication of the central cell in Arabidopsis thaliana. Auxin is sufficient to trigger central cell division and is necessary for correct endosperm development, a process dependent on the MADS-box transcription factor AGL62 (AGAMOUS-LIKE 62). We propose that the epigenetic regulators of the Polycomb group (PcG) family block central cell division before fertilization by repressing the expression of auxin biosynthesis genes in the female gametophyte.
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http://dx.doi.org/10.1038/nplants.2015.184DOI Listing
November 2015

Phloem development: current knowledge and future perspectives.

Am J Bot 2014 Sep 2;101(9):1393-402. Epub 2014 Sep 2.

Institute of Biotechnology, Department of Bio and Environmental Sciences, University of Helsinki, FIN-00014, Finland.

Phloem, as a major tissue mediating long-distance communication, has been an object of extensive research ever since its structure was first reported in 1837. Functional phloem consists of sieve elements (SEs) and companion cells (CCs). While SEs are enucleated conducting cells in the phloem, CCs are cells with intact cellular components and are known to support the functioning of SEs. CCs are closely linked to SEs by symplastic connections mediated by plasmodesmata (PD). Sieve elements are notoriously sensitive to manipulation, which has hampered efforts to investigate their structure using microscopy or histology; phloem thus remains a mysterious tissue almost 200 yr after its discovery. Nevertheless, consistent efforts have overcome many of the technical barriers and generated considerable amounts of data about the structure and function of phloem. Advances in the 1950s and 1960s significantly improved our understanding of phloem anatomy and function. A major function of the phloem is to establish symplastic connections throughout the plant body, delivering nutrients and various signaling molecules, which play pivotal roles in growth and development. Despite the importance of phloem, details about the molecular mechanisms responsible for the establishment and maintenance of phloem continuity remain elusive.
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http://dx.doi.org/10.3732/ajb.1400197DOI Listing
September 2014

Polycomb group proteins are required to couple seed coat initiation to fertilization.

Proc Natl Acad Sci U S A 2011 Dec 5;108(51):20826-31. Epub 2011 Dec 5.

Department of Biology and Zurich-Basel Plant Science Center, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland.

Seed development in flowering plants is initiated after a double fertilization event leading to the formation of zygotic embryo and endosperm tissues surrounded by the maternally derived seed coat. Although the seed coat does not take part in the fertilization process it develops immediately after fertilization, implicating a signaling mechanism from zygotic tissues to the surrounding maternal tissues. We addressed the question of the underlying mechanisms repressing seed coat development before fertilization and initiating seed coat development after fertilization by analyzing combinations of mutants that initiate seed development in the absence of fertilization. We discovered that seed coat development is actively repressed before fertilization by dosage-sensitive Polycomb group proteins acting in maternal tissues surrounding the female gametophyte. This repression is relieved after fertilization by a signal that is formed by the sexual endosperm. Fertilization is required for signal formation, as asexually formed endosperm fails to effectively initiate seed coat development in mutants with uncompromised maternal Polycomb group function. Mutants for the MADS-box transcription factor AGL62 initiate embryo and endosperm formation but fail to develop a seed coat, implicating AGL62 expression in the endosperm as a requirement for signal initiation. Together, our results provide evidence that fertilization of the central cell generates a signal that relieves Polycomb group-mediated repression in the surrounding maternal tissues to initiate seed coat formation.
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http://dx.doi.org/10.1073/pnas.1117111108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3251106PMC
December 2011

High-resolution analysis of parent-of-origin allelic expression in the Arabidopsis Endosperm.

PLoS Genet 2011 Jun 16;7(6):e1002126. Epub 2011 Jun 16.

Department of Biology and Zurich-Basel Plant Science Center, Swiss Federal Institute of Technology, Zurich, Switzerland.

Genomic imprinting is an epigenetic phenomenon leading to parent-of-origin specific differential expression of maternally and paternally inherited alleles. In plants, genomic imprinting has mainly been observed in the endosperm, an ephemeral triploid tissue derived after fertilization of the diploid central cell with a haploid sperm cell. In an effort to identify novel imprinted genes in Arabidopsis thaliana, we generated deep sequencing RNA profiles of F1 hybrid seeds derived after reciprocal crosses of Arabidopsis Col-0 and Bur-0 accessions. Using polymorphic sites to quantify allele-specific expression levels, we could identify more than 60 genes with potential parent-of-origin specific expression. By analyzing the distribution of DNA methylation and epigenetic marks established by Polycomb group (PcG) proteins using publicly available datasets, we suggest that for maternally expressed genes (MEGs) repression of the paternally inherited alleles largely depends on DNA methylation or PcG-mediated repression, whereas repression of the maternal alleles of paternally expressed genes (PEGs) predominantly depends on PcG proteins. While maternal alleles of MEGs are also targeted by PcG proteins, such targeting does not cause complete repression. Candidate MEGs and PEGs are enriched for cis-proximal transposons, suggesting that transposons might be a driving force for the evolution of imprinted genes in Arabidopsis. In addition, we find that MEGs and PEGs are significantly faster evolving when compared to other genes in the genome. In contrast to the predominant location of mammalian imprinted genes in clusters, cluster formation was only detected for few MEGs and PEGs, suggesting that clustering is not a major requirement for imprinted gene regulation in Arabidopsis.
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http://dx.doi.org/10.1371/journal.pgen.1002126DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3116908PMC
June 2011

'happy on norflurazon' (hon) mutations implicate perturbance of plastid homeostasis with activating stress acclimatization and changing nuclear gene expression in norflurazon-treated seedlings.

Plant J 2011 Mar 5;65(5):690-702. Epub 2011 Jan 5.

Institute of Plant Sciences, Plant Genetics, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland.

Various mutant screens have been undertaken to identify constituents involved in the transmission of signals from the plastid to the nucleus. Many of these screens have been performed using carotenoid-deficient plants grown in the presence of norflurazon (NF), an inhibitor of phytoene desaturase. NF-treated plants are bleached and suppress the expression of nuclear genes encoding chloroplast proteins. Several genomes uncoupled (gun) mutants have been isolated that de-repress the expression of these nuclear genes. In the present study, a genetic screen has been established that circumvents severe photo-oxidative stress in NF-treated plants. Under these modified screening conditions, happy on norflurazon (hon) mutants have been identified that, like gun mutants, de-repress expression of the Lhcb gene, encoding a light-harvesting chlorophyll protein, but, in contrast to wild-type and gun mutants, are green in the presence of NF. hon mutations disturb plastid protein homeostasis, thereby activating plastid signaling and inducing stress acclimatization. Rather than defining constituents of a retrograde signaling pathway specifically associated with the NF-induced suppression of nuclear gene expression, as proposed for gun, hon mutations affect Lhcb expression more indirectly prior to initiation of plastid signaling in NF-treated seedlings. They pre-condition seedlings by inducing stress acclimatization, thereby attenuating the impact of a subsequent NF treatment.
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http://dx.doi.org/10.1111/j.1365-313X.2010.04454.xDOI Listing
March 2011

H3K27me3 profiling of the endosperm implies exclusion of polycomb group protein targeting by DNA methylation.

PLoS Genet 2010 Oct 7;6(10). Epub 2010 Oct 7.

Department of Biology and Zurich-Basel Plant Science Center, Swiss Federal Institute of Technology, Zurich, Switzerland.

Polycomb group (PcG) proteins act as evolutionary conserved epigenetic mediators of cell identity because they repress transcriptional programs that are not required at particular developmental stages. Each tissue is likely to have a specific epigenetic profile, which acts as a blueprint for its developmental fate. A hallmark for Polycomb Repressive Complex 2 (PRC2) activity is trimethylated lysine 27 on histone H3 (H3K27me3). In plants, there are distinct PRC2 complexes for vegetative and reproductive development, and it was unknown so far whether these complexes have target gene specificity. The Fertilization Independent Seed (FIS) PRC2 complex is specifically expressed in the endosperm and is required for its development; loss of FIS function causes endosperm hyperproliferation and seed abortion. The endosperm nourishes the embryo, similar to the physiological function of the placenta in mammals. We established the endosperm H3K27me3 profile and identified specific target genes of the FIS complex with functional roles in endosperm cellularization and chromatin architecture, implicating that distinct PRC2 complexes have a subset of specific target genes. Importantly, our study revealed that selected transposable elements and protein coding genes are specifically targeted by the FIS PcG complex in the endosperm, whereas these elements and genes are densely marked by DNA methylation in vegetative tissues, suggesting that DNA methylation prevents targeting by PcG proteins in vegetative tissues.
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http://dx.doi.org/10.1371/journal.pgen.1001152DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2951372PMC
October 2010