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  • 1.
    Boutté, Yohann
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Frescatada-Rosa, Márcia
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Men, Shuzhen
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Chow, Cheung-Ming
    Ebine, Kazuo
    Gustavsson, Anna
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Johansson, Lenore
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ueda, Takashi
    Moore, Ian
    Jürgens, Gerd
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Endocytosis restricts Arabidopsis KNOLLE syntaxin to the cell division plane during late cytokinesis2010In: EMBO Journal, ISSN 0261-4189, E-ISSN 1460-2075, Vol. 29, no 3, p. 546-58Article in journal (Refereed)
    Abstract [en]

    Cytokinesis represents the final stage of eukaryotic cell division during which the cytoplasm becomes partitioned between daughter cells. The process differs to some extent between animal and plant cells, but proteins of the syntaxin family mediate membrane fusion in the plane of cell division in diverse organisms. How syntaxin localization is kept in check remains elusive. Here, we report that localization of the Arabidopsis KNOLLE syntaxin in the plane of cell division is maintained by sterol-dependent endocytosis involving a clathrin- and DYNAMIN-RELATED PROTEIN1A-dependent mechanism. On genetic or pharmacological interference with endocytosis, KNOLLE mis-localizes to lateral plasma membranes after cell-plate fusion. Fluorescence-loss-in-photo-bleaching and fluorescence-recovery-after-photo-bleaching experiments reveal lateral diffusion of GFP-KNOLLE from the plane of division to lateral membranes. In an endocytosis-defective sterol biosynthesis mutant displaying lateral KNOLLE diffusion, KNOLLE secretory trafficking remains unaffected. Thus, restriction of lateral diffusion by endocytosis may serve to maintain specificity of syntaxin localization during late cytokinesis.

  • 2.
    Boutté, Yohann
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Cellular processes relying on sterol function in plants2009In: Current opinion in plant biology, ISSN 1369-5266, E-ISSN 1879-0356, Vol. 12, no 6, p. 705-713Article in journal (Refereed)
    Abstract [en]

    Sterols are lipophilic membrane components essential for diverse cellular functions. The plant sterol biosynthesis pathway has largely been defined by biochemical approaches. Sterol function has been investigated by the pharmacological and genetic manipulation of sterol biosynthesis. However, mechanisms by which sterols influence cellular processes and targets of sterol function remain largely unknown. During the last two years, new Arabidopsis sterol biosynthesis mutants have been characterized. Their analysis has revealed the contributions of known and alternative routes of sterol biosynthesis to various cellular processes. Subcellular localization and trafficking of a sterol-binding protein have been investigated and first steps towards in vivo characterization of sterol-enriched membrane domains have been taken. Finally, mechanistic insight into the role of plant sterols during endocytosis and the establishment of cell polarity has been obtained.

  • 3. Boutté, Yohann
    et al.
    Ikeda, Yoshihisa
    Grebe, Markus
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Mechanisms of auxin-dependent cell and tissue polarity2007In: Current opinion in plant biology, ISSN 1369-5266, E-ISSN 1879-0356, Vol. 10, no 6, p. 616-623Article in journal (Refereed)
    Abstract [en]

    The establishment of cellular asymmetries and their coordination within the tissue layer are fundamental to the development of multicellular organisms. In plants, the induction and coordination of cell polarity have classically been attributed to involve the hormone auxin and its flow. However, the underlying mechanisms have only recently been addressed at the molecular level. We review progress on the characterisation of the auxin influx and efflux carrier properties of specific plasma membrane proteins, mechanisms underlying their delivery to and internalisation from the plasma membrane, their endocytic transport and degradation. We discuss mechanisms of auxin gradient, transport and response action during the coordination of polarity, along with the downstream involvement of Rho-of-plant small GTPases during the execution of cell polarity.

  • 4.
    Boutté, Yohann
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Men, Shuzhen
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Fluorescent in situ visualization of sterols in Arabidopsis roots2011In: Nature Protocols, ISSN 1754-2189, E-ISSN 1750-2799, Vol. 6, no 4, p. 446-456Article in journal (Refereed)
    Abstract [en]

    Sterols are eukaryotic membrane components with crucial roles in diverse cellular processes. Elucidation of sterol function relies on development of tools for in situ sterol visualization. Here we describe protocols for in situ sterol localization in Arabidopsis thaliana root cells, using filipin as a specific probe for detection of fluorescent filipin-sterol complexes. Currently, filipin is the only established tool for sterol visualization in plants. Filipin labeling can be performed on aldehyde-fixed samples, largely preserving fluorescent proteins and being compatible with immunocytochemistry. Filipin can also be applied for probing live cells, taking into account the fact that it inhibits sterol-dependent endocytosis. The experimental procedures described are designed for fluorescence detection by confocal laser-scanning microscopy with excitation of filipin-sterol complexes at 364 nm. The protocols require 1 d for sterol covisualization with fluorescent proteins in fixed or live roots and 2 d for immunocytochemistry on whole-mount roots.

  • 5. Fischer, Urs
    et al.
    Ikeda, Yoshihisa
    Grebe, Markus
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Planar polarity of root hair positioning in Arabidopsis2007In: Biochemical Society Transactions, ISSN 0300-5127, E-ISSN 1470-8752, Vol. 35, no Pt 1, p. 149-151Article in journal (Refereed)
    Abstract [en]

    The co-ordinated polarity of cells within the plane of a single tissue layer (planar polarity) is intensively studied in animal epithelia but has only recently been systematically analysed in plants. The polar positioning of hairs in the root epidermis of Arabidopsis thaliana provides an easily accessible system for the functional dissection of a plant-specific planar polarity. Recently, mutants originally isolated in genetic screens for defects in root hair morphogenesis and changes in the sensitivity to or the production of the plant hormones auxin and ethylene have identified players that contribute to polar root hair placement. Here, we summarize and discuss recent progress in research on polar root hair positioning from studies in Arabidopsis.

  • 6.
    Fischer, Urs
    et al.
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Ikeda, Yoshihisa
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Ljung, Karin
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Serralbo, Olivier
    Singh, Manoj
    Heidstra, Renze
    Palme, Klaus
    Scheres, Ben
    Grebe, Markus
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Vectorial information for Arabidopsis planar polarity is mediated by combined AUX1, EIN2, and GNOM activity2006In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 16, no 21, p. 2143-2149Article in journal (Refereed)
    Abstract [en]

    Cell polarity is commonly coordinated within the plane of a single tissue layer (planar polarity), and hair positioning has been exploited as a simple marker for planar polarization of animal epithelia . The root epidermis of the plant Arabidopsis similarly reveals planar polarity of hair localization close to root tip-oriented (basal) ends of hair-forming cells . Hair position is directed toward a concentration maximum of the hormone auxin in the root tip , but mechanisms driving this plant-specific planar polarity remain elusive. Here, we report that combinatorial action of the auxin influx carrier AUX1, ETHYLENE-INSENSITIVE2 (EIN2) , and GNOM genes mediates the vector for coordinate hair positioning. In aux1;ein2;gnom eb triple mutant roots, hairs display axial (apical or basal) instead of coordinate polar (basal) position, and recruitment of Rho-of-Plant (ROP) GTPases to the hair initiation site reveals the same polar-to-axial switch. The auxin concentration gradient is virtually abolished in aux1;ein2;gnom eb roots, where locally applied auxin can coordinate hair positioning. Moreover, auxin overproduction in sectors of wild-type roots enhances planar ROP and hair polarity over long and short distances. Hence, auxin may provide vectorial information for planar polarity that requires combinatorial AUX1, EIN2, and GNOM activity upstream of ROP positioning.

  • 7. Fischer, Urs
    et al.
    Men, Shuzhen
    Grebe, Markus
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Lipid function in plant cell polarity.2004In: Current opinion in plant biology, ISSN 1369-5266, E-ISSN 1879-0356, Vol. 7, no 6, p. 670-6Article in journal (Refereed)
    Abstract [en]

    The establishment and maintenance of cell polarity play pivotal roles during plant development. During the past five years, proteins that are required for different aspects of plant cell polarity have been identified. However, the functions of lipids and their interactions with proteins that mediate polarity remained largely unaddressed. Recent genetic studies have discovered cell and tissue polarity mutants that have defects in sterol composition, glycosylphosphatidylinositol-anchored proteins, glycosylphosphatidylinositol biosynthesis and phospholipid signalling. Analyses of the affected gene products have provided a first glance at the roles of lipids in cell polarity signalling, as well as in the trafficking and anchoring of polar proteins.

  • 8.
    Frescatada-Rosa, Marcia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Stanislas, Thomas
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Backues, Steven K.
    Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA.
    Reichardt, Ilka
    Department of Developmental Genetics, Centre for Plant Molecular Biology, University of Tübingen, Tübingen, Germany.
    Men, Shuzhen
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Boutte, Yohann
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Jürgens, Gerd
    Department of Developmental Genetics, Centre for Plant Molecular Biology, University of Tübingen, Tübingen, Germany.
    Moritz, Thomas
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Bednarek, Sebastian Y.
    Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Institute for Biochemistry and Biology, Plant Physiology, University of Potsdam, Potsdam-Golm, Germany.
    High lipid order of Arabidopsis cell-plate membranes mediated by sterol and DYNAMIN-RELATED PROTEIN1A function2014In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 80, no 5, p. 745-757Article in journal (Refereed)
    Abstract [en]

    Membranes of eukaryotic cells contain high lipid-order sterol-rich domains that are thought to mediate temporal and spatial organization of cellular processes. Sterols are crucial for execution of cytokinesis, the last stage of cell division, in diverse eukaryotes. The cell plate of higher-plant cells is the membrane structure that separates daughter cells during somatic cytokinesis. Cell-plate formation in Arabidopsis relies on sterol- and DYNAMIN-RELATED PROTEIN1A (DRP1A)-dependent endocytosis. However, functional relationships between lipid membrane order or lipid packing and endocytic machinery components during eukaryotic cytokinesis have not been elucidated. Using ratiometric live imaging of lipid order-sensitive fluorescent probes, we show that the cell plate of Arabidopsis thaliana represents a dynamic, high lipid-order membrane domain. The cell-plate lipid order was found to be sensitive to pharmacological and genetic alterations of sterol composition. Sterols co-localize with DRP1A at the cell plate, and DRP1A accumulates in detergent-resistant membrane fractions. Modifications of sterol concentration or composition reduce cell-plate membrane order and affect DRP1A localization. Strikingly, DRP1A function itself is essential for high lipid order at the cell plate. Our findings provide evidence that the cell plate represents a high lipid-order domain, and pave the way to explore potential feedback between lipid order and function of dynamin-related proteins during cytokinesis.

  • 9. Friml, Jirí
    et al.
    Benfey, Philip
    Benková, Eva
    Bennett, Malcolm
    Berleth, Thomas
    Geldner, Niko
    Grebe, Markus
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Heisler, Marcus
    Hejátko, Jan
    Jürgens, Gerd
    Laux, Thomas
    Lindsey, Keith
    Lukowitz, Wolfgang
    Luschnig, Christian
    Offringa, Remko
    Scheres, Ben
    Swarup, Ranjan
    Torres-Ruiz, Ramón
    Weijers, Dolf
    Zazímalová, Eva
    Apical-basal polarity: why plant cells don't stand on their heads (Letters)2006In: Trends in Plant Science, ISSN 1360-1385, E-ISSN 1878-4372, Vol. 11, no 1, p. 12-14Article in journal (Refereed)
  • 10. Gendre, Delphine
    et al.
    Baral, Anirban
    Dang, Xie
    Esnay, Nicolas
    Boutté, Yohann
    Stanislas, Thomas
    Vain, Thomas
    Claverol, Stéphane
    Gustavsson, Anna
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Lin, Deshu
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Institute of Biochemistry and Biology, Plant Physiology, Universityof Potsdam, Germany.
    Bhalerao, Rishikesh P.
    Rho-of-plant activated root hair formation requires Arabidopsis YIP4a/b gene function2019In: Development, ISSN 0950-1991, E-ISSN 1477-9129, Vol. 146, no 5, article id dev168559Article in journal (Refereed)
    Abstract [en]

    Root hairs are protrusions from root epidermal cells with crucial roles in plant soil interactions. Although much is known about patterning, polarity and tip growth of root hairs, contributions of membrane trafficking to hair initiation remain poorly understood. Here, we demonstrate that the trans-Golgi network-localized YPT-INTERACTING PROTEIN 4a and YPT-INTERACTING PROTEIN 4b (YIP4a/b) contribute to activation and plasma membrane accumulation of Rho-of-plant (ROP) small GTPases during hair initiation, identifying YIP4a/b as central trafficking components in ROP-dependent root hair formation.

  • 11.
    Gendre, Delphine
    et al.
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences.
    Oh, Jaesung
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences.
    Boutté, Yohann
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences.
    Best, Jacob G
    Samuels, Lacey
    Nilsson, Robert
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences.
    Uemura, Tomohiro
    Marchant, Alan
    Bennett, Malcolm J
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bhalerao, Rishikesh P
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences.
    Conserved Arabidopsis ECHIDNA protein mediates trans-Golgi-network trafficking and cell elongation2011In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 19, p. 8048-8053Article in journal (Refereed)
    Abstract [en]

    Multiple steps of plant growth and development rely on rapid cell elongation during which secretory and endocytic trafficking via the trans-Golgi network (TGN) plays a central role. Here, we identify the ECHIDNA (ECH) protein from Arabidopsis thaliana as a TGN-localized component crucial for TGN function. ECH partially complements loss of budding yeast TVP23 function and a Populus ECH complements the Arabidopsis ech mutant, suggesting functional conservation of the genes. Compared with wild-type, the Arabidopsis ech mutant exhibits severely perturbed cell elongation as well as defects in TGN structure and function, manifested by the reduced association between Golgi bodies and TGN as well as mislocalization of several TGN-localized proteins including vacuolar H(+)-ATPase subunit a1 (VHA-a1). Strikingly, ech is defective in secretory trafficking, whereas endocytosis appears unaffected in the mutant. Some aspects of the ech mutant phenotype can be phenocopied by treatment with a specific inhibitor of vacuolar H(+)-ATPases, concanamycin A, indicating that mislocalization of VHA-a1 may account for part of the defects in ech. Hence, ECH is an evolutionarily conserved component of the TGN with a central role in TGN structure and function.

  • 12.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Cell polarity: lateral perspectives2010In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 20, no 10, p. R446-R448Article in journal (Refereed)
    Abstract [en]

    The outer and inner (lateral) plasma membranes of the outermost cell layer in plants provide selective barriers to the environment. Recent studies provide perspectives on how asymmetric protein localization is established at lateral membranes.

  • 13.
    Grebe, Markus
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Growth by auxin: when a weed needs acid2005In: Science (New York, N.Y.), ISSN 1095-9203, Vol. 310, no 5745, p. 60-1Article in journal (Refereed)
    Abstract [en]

    In his Perspective, Grebe discusses how a plant proton pump residing in intracellular compartments, rather than in the plasma membrane of the cell surface, regulates growth and development. The pump modulates the expression at the plasma membrane of both a transporter for the hormone auxin and another proton pump. These findings open new views on how plants regulate cell wall acidity and hormone transport during development.

  • 14.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Out of the shade and into the light2011In: Nature Cell Biology, ISSN 1465-7392, E-ISSN 1476-4679, Vol. 13, no 4, p. 347-349Article in journal (Refereed)
    Abstract [en]

    Plants reach for the sun by avoiding the shade and by directly growing towards the light. Two studies now suggest that the polar relocation of PIN3, a transporter directing the flow of the plant hormone auxin, drives both growth processes. PIN3 repolarization occurs downstream of shade perception through phytochrome photoreceptors, whereas blue light perceived by phototropin initiates polar recycling of PIN3 and growth towards the light.

  • 15.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Plant biology: Unveiling the Casparian strip.2011In: Nature, ISSN 1476-4687, Vol. 473, no 7347, p. 294-5Article in journal (Refereed)
  • 16.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    The patterning of epidermal hairs in Arabidopsis: updated2012In: Current opinion in plant biology, ISSN 1369-5266, E-ISSN 1879-0356, Vol. 15, no 1, p. 31-37Article, review/survey (Refereed)
    Abstract [en]

    Epidermal hairs of Arabidopsis thaliana emerge in regular spacing patterns providing excellent model systems for studies of biological pattern formation. A number of root-hair and leaf-trichome patterning mutants and tools for cell-specific and tissue-specific manipulation of patterning protein activities have been combined in cycles of experimentation and mathematical modelling. These approaches have provided insight into molecular mechanisms of epidermal patterning. During the last two years, endoreplication has, unexpectedly, been found to control cell-fate maintenance during trichome patterning. New genetic interactions between a downstream, positive transcriptional regulator and lateral inhibitors of trichome or non-root-hair fate specification have been uncovered. A lateral inhibitor and a new positive regulator have been identified as major loci affecting trichome patterning in natural Arabidopsis populations. Finally, factors that modify root-hair patterning from the underlying cell layer have been discovered.

  • 17.
    Grebe, Markus
    Institutionen för skoglig genetik och växtfysiologi, Sveriges Lantbruksuniversitet, Umeå.
    Ups and downs of tissue and planar polarity in plants.2004In: Bioessays, ISSN 0265-9247, E-ISSN 1521-1878, Vol. 26, no 7, p. 719-29Article in journal (Refereed)
    Abstract [en]

    The polar orientation of cells within a tissue is an intensively studied research area in animal cells. The term planar polarity refers to the common polar arrangement of cells within the plane of an epithelium. In plants, the subcellular analysis of tissue polarity has been limited by the lack of appropriate markers. Recently, research on plant tissue polarity has come of age. Advances are based on studies of Arabidopsis patterning, cell polarity and auxin transport mutants employing the coordinated, polar localization of auxin transporters and the planar polarity of root epidermal hairs as markers. These approaches have revealed auxin transport and response, vesicular trafficking, membrane sterol and cytoskeletal requirements of tissue polarity. This review summarizes recent progress in research on vascular tissue and planar epidermal polarity in the Arabidopsis root and compares it to findings on planar polarity in animals and cell polarity in yeast.

  • 18.
    Ikeda, Yoshihisa
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Men, Shuzhen
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Fischer, Urs
    Stepanova, Anna N
    Alonso, José M
    Ljung, Karin
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Local auxin biosynthesis modulates gradient-directed planar polarity in Arabidopsis2009In: Nature Cell Biology, ISSN 1465-7392, E-ISSN 1476-4679, Vol. 11, no 6, p. 731-738Article in journal (Refereed)
    Abstract [en]

    The coordination of cell polarity within the plane of a single tissue layer (planar polarity) is a crucial task during development of multicellular organisms. Mechanisms underlying establishment of planar polarity, however, differ substantially between plants and animals. In Arabidopsis thaliana, planar polarity of root-hair positioning along epidermal cells is coordinated towards maximum concentration of an auxin gradient in the root tip. This gradient has been hypothesized to be sink-driven and computational modelling suggests that auxin efflux carrier activity may be sufficient to generate the gradient in the absence of auxin biosynthesis in the root. Here, we demonstrate that the Raf-like kinase CONSTITUTIVE TRIPLE RESPONSE1 (CTR1; Refs 8, 9) acts as a concentration-dependent repressor of a biosynthesis-dependent auxin gradient that modulates planar polarity in the root tip. We analysed auxin biosynthesis and concentration gradients in a variety of root-hair-position mutants affected in CTR1 activity, auxin biosynthesis and transport. Our results reveal that planar polarity relies on influx- and efflux-carrier-mediated auxin redistribution from a local biosynthesis maximum. Thus, a local source of auxin biosynthesis contributes to gradient homeostasis during long-range coordination of cellular morphogenesis.

  • 19.
    Kiefer, Christian S.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Claes, Andrea R.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Nzayisenga, Jean-Claude
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Pietra, Stefano
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Stanislas, Thomas
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Hueser, Anke
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ikeda, Yoshihisa
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). nstitute of Biochemistry and Biology, Plant Physiology, University of Potsdam, Germany.
    Arabidopsis AIP1-2 restricted by WER-mediated patterning modulates planar polarity2015In: Development, ISSN 0950-1991, E-ISSN 1477-9129, Vol. 142, no 1, p. 151-161Article in journal (Refereed)
    Abstract [en]

    The coordination of cell polarity within the plane of the tissue layer (planar polarity) is crucial for the development of diverse multicellular organisms. Small Rac/Rho-family GTPases and the actin cytoskeleton contribute to planar polarity formation at sites of polarity establishment in animals and plants. Yet, upstream pathways coordinating planar polarity differ strikingly between kingdoms. In the root of Arabidopsis thaliana, a concentration gradient of the phytohormone auxin coordinates polar recruitment of Rho-of-plant (ROP) to sites of polar epidermal hair initiation. However, little is known about cytoskeletal components and interactions that contribute to this planar polarity or about their relation to the patterning machinery. Here, we show that ACTIN7 (ACT7) represents a main actin isoform required for planar polarity of root hair positioning, interacting with the negative modulator ACTIN-INTERACTING PROTEIN1-2 (AIP1-2). ACT7, AIP1-2 and their genetic interaction are required for coordinated planar polarity of ROP downstream of ethylene signalling. Strikingly, AIP1-2 displays hair cell file-enriched expression, restricted by WEREWOLF (WER)-dependent patterning and modified by ethylene and auxin action. Hence, our findings reveal AIP1-2, expressed under control of the WER-dependent patterning machinery and the ethylene signalling pathway, as a modulator of actin-mediated planar polarity.

  • 20. Krupinski, Pawel
    et al.
    Bozorg, Behruz
    Larsson, André
    Pietra, Stefano
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Institute of Biochemistry and Biology, Plant Physiology, University of Potsdam, Potsdam, Germany.
    Jönsson, Henrik
    A Model Analysis of Mechanisms for Radial Microtubular Patterns at Root Hair Initiation Sites2016In: Frontiers in Plant Science, ISSN 1664-462X, E-ISSN 1664-462X, Vol. 7, article id 1560Article in journal (Refereed)
    Abstract [en]

    Plant cells have two main modes of growth generating anisotropic structures. Diffuse growth where whole cell walls extend in specific directions, guided by anisotropically positioned cellulose fibers, and tip growth, with inhomogeneous addition of new cell wall material at the tip of the structure. Cells are known to regulate these processes via molecular signals and the cytoskeleton. Mechanical stress has been proposed to provide an input to the positioning of the cellulose fibers via cortical microtubules in diffuse growth. In particular, a stress feedback model predicts a circumferential pattern of fibers surrounding apical tissues and growing primordia, guided by the anisotropic curvature in such tissues. In contrast, during the initiation of tip growing root hairs, a star-like radial pattern has recently been observed. Here, we use detailed finite element models to analyze how a change in mechanical properties at the root hair initiation site can lead to star-like stress patterns in order to understand whether a stress-based feedback model can also explain the microtubule patterns seen during root hair initiation. We show that two independent mechanisms, individually or combined, can be sufficient to generate radial patterns. In the first, new material is added locally at the position of the root hair. In the second, increased tension in the initiation area provides a mechanism. Finally, we describe how a molecular model of Rho-of-plant (ROP) GTPases activation driven by auxin can position a patch of activated ROP protein basally along a 2D root epidermal cell plasma membrane, paving the way for models where mechanical and molecular mechanisms cooperate in the initial placement and outgrowth of root hairs.

  • 21.
    Mao, Hailiang
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Aryal, Bibek
    Langenecker, Tobias
    Hagmann, Jörg
    Geisler, Markus
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Institute of Biochemistry and Biology, Department of Plant Physiology, University of Potsdam, Potsdam-Golm, Germany.
    Arabidopsis BTB/POZ protein-dependent PENETRATION3 trafficking and disease susceptibility2017In: Nature Plants, ISSN 2055-026X, Vol. 3, no 11, p. 854-858Article in journal (Refereed)
    Abstract [en]

    The outermost cell layer of plant roots (epidermis) constantly encounters environmental challenges. The epidermal outer plasma membrane domain harbours the PENETRATION3 (PEN3)/ABCG36/PDR8 ATP-binding cassette transporter that confers non-host resistance to several pathogens. Here, we show that the Arabidopsis ENDOPLASMIC RETICULUM-ARRESTED PEN3 (EAP3) BTB/POZ-domain protein specifically mediates PEN3 exit from the endoplasmic reticulum and confers resistance to a root-penetrating fungus, providing prime evidence for BTB/POZ-domain protein-dependent membrane trafficking underlying disease resistance.

  • 22.
    Mao, Hailiang
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Nakamura, Moritaka
    Viotti, Corrado
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Institute of Biochemistry and Biology, Plant Physiology, University of Potsdam, Germany.
    A Framework for Lateral Membrane Trafficking and Polar Tethering of the PEN3 ATP-Binding Cassette Transporter2016In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 172, no 4, p. 2245-2260Article in journal (Refereed)
    Abstract [en]

    The outermost cell layer of plants, the epidermis, and its outer (lateral) membrane domain facing the environment are continuously challenged by biotic and abiotic stresses. Therefore, the epidermis and the outer membrane domain provide important selective and protective barriers. However, only a small number of specifically outer membrane-localized proteins are known. Similarly, molecular mechanisms underlying the trafficking and the polar placement of outer membrane domain proteins require further exploration. Here, we demonstrate that ACTIN7 (ACT7) mediates trafficking of the PENETRATION3 (PEN3) outer membrane protein from the trans-Golgi network (TGN) to the plasma membrane in the root epidermis of Arabidopsis (Arabidopsis thaliana) and that actin function contributes to PEN3 endocytic recycling. In contrast to such generic ACT7-dependent trafficking from the TGN, the EXOCYST84b (EXO84b) tethering factor mediates PEN3 outer-membrane polarity. Moreover, precise EXO84b placement at the outer membrane domain itself requires ACT7 function. Hence, our results uncover spatially and mechanistically distinct requirements for ACT7 function during outer lateral membrane cargo trafficking and polarity establishment. They further identify an exocyst tethering complex mediator of outer lateral membrane cargo polarity.

  • 23.
    Men, Shuzhen
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Boutté, Yohann
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ikeda, Yoshihisa
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Li, Xugang
    Palme, Klaus
    Stierhof, York-Dieter
    Hartmann, Marie-Andrée
    Moritz, Thomas
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Sterol-dependent endocytosis mediates post-cytokinetic acquisition of PIN2 auxin efflux carrier polarity2008In: Nature Cell Biology, ISSN 1465-7392, Vol. 10, no 2, p. 237-244Article in journal (Refereed)
    Abstract [en]

    The polarization of yeast and animal cells relies on membrane sterols for polar targeting of proteins to the plasma membrane, their polar endocytic recycling and restricted lateral diffusion1, 2, 3, 4. However, little is known about sterol function in plant-cell polarity5. Directional root growth along the gravity vector requires polar transport of the plant hormone auxin. In Arabidopsis, asymmetric plasma membrane localization of the PIN–FORMED2 (PIN2) auxin transporter directs root gravitropism6, 7, 8, 9, 10. Although the composition of membrane sterols influences gravitropism and localization of two other PIN proteins11, it remains unknown how sterols contribute mechanistically to PIN polarity. Here, we show that correct membrane sterol composition is essential for the acquisition of PIN2 polarity. Polar PIN2 localization is defective in the sterol-biosynthesis mutant cyclopropylsterol isomerase1-1 (cpi1-1) which displays altered sterol composition, PIN2 endocytosis, and root gravitropism. At the end of cytokinesis, PIN2 localizes initially to both newly formed membranes but subsequently disappears from one. By contrast, PIN2 frequently remains at both daughter membranes in endocytosis-defective cpi1-1 cells. Hence, sterol composition affects post-cytokinetic acquisition of PIN2 polarity by endocytosis, suggesting a mechanism for sterol action on establishment of asymmetric protein localization.

  • 24. Nakamura, Moritaka
    et al.
    Claes, Andrea R.
    Grebe, Tobias
    Hermkes, Rebecca
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Viotti, Corrado
    Ikeda, Yoshihisa
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Auxin and ROP GTPase Signaling of Polar Nuclear Migration in Root Epidermal Hair Cells2018In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 176, no 1, p. 378-391Article in journal (Refereed)
    Abstract [en]

    Polar nuclear migration is crucial during the development of diverse eukaryotes. In plants, root hair growth requires polar nuclear migration into the outgrowing hair. However, knowledge about the dynamics and the regulatory mechanisms underlying nuclear movements in root epidermal cells remains limited. Here, we show that both auxin and Rho-of-Plant (ROP) signaling modulate polar nuclear position at the inner epidermal plasma membrane domain oriented to the cortical cells during cell elongation as well as subsequent polar nuclear movement to the outer domain into the emerging hair bulge in Arabidopsis (Arabidopsis thaliana). Auxin signaling via the nuclear AUXIN RESPONSE FACTOR7 (ARF7)/ARF19 and INDOLE ACETIC ACID7 pathway ensures correct nuclear placement toward the inner membrane domain. Moreover, precise inner nuclear placement relies on SPIKE1 Rho-GEF, SUPERCENTIPEDE1 Rho-GDI, and ACTIN7 (ACT7) function and to a lesser extent on VTI11 vacuolar SNARE activity. Strikingly, the directionality and/or velocity of outer polar nuclear migration into the hair outgrowth along actin strands also are ACT7 dependent, auxin sensitive, and regulated by ROP signaling. Thus, our findings provide a founding framework revealing auxin and ROP signaling of inner polar nuclear position with some contribution by vacuolar morphology and of actin-dependent outer polar nuclear migration in root epidermal hair cells.

  • 25. Nakamura, Moritaka
    et al.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Institute of Biochemistry and Biology, Plant Physiology, University of Potsdam, Germany.
    Outer, inner and planar polarity in the Arabidopsis root2018In: Current opinion in plant biology, ISSN 1369-5266, E-ISSN 1879-0356, Vol. 41, p. 46-53Article, review/survey (Refereed)
    Abstract [en]

    Plant roots control uptake of water and nutrients and cope with environmental challenges. The root epidermis provides the first selective interface for nutrient absorption, while the endodermis produces the main apoplastic diffusion barrier in the form of a structure called the Casparian strip. The positioning of root hairs on epidermal cells, and of the Casparian strip around endodermal cells, requires asymmetries along cellular axes (cell polarity). Cell polarity is termed planar polarity, when coordinated within the plane of a given tissue layer. Here, we review recent molecular advances towards understanding both the polar positioning of the proteo-lipid membrane domain instructing root hair initiation, and the cytoskeletal, trafficking and polar tethering requirements of proteins at outer or inner plasma membrane domains. Finally, we highlight progress towards understanding mechanisms of Casparian strip formation and underlying endodermal cell polarity.

  • 26.
    Nakamura, Moritaka
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kiefer, Christian S.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Planar polarity, tissue polarity and planar morphogenesis in plants2012In: Current opinion in plant biology, ISSN 1369-5266, E-ISSN 1879-0356, Vol. 15, no 6, p. 593-600Article, review/survey (Refereed)
    Abstract [en]

    Plant tissues commonly undergo morphogenesis within a single tissue layer or between associated cells of the same tissue type such as vascular cells. Tissue morphogenesis may rely on an underlying tissue polarity marked by coordinated unidirectional asymmetric localisation of molecules to ends of cells. When observed in the plane of the tissue layer this is referred to as planar polarity and planar morphogenesis. However, planar morphogenesis can also involve multidirectional or differential growth of cells relying on cell-cell communication. Here, we review recent progress towards an understanding of hormonal coordination and molecular mechanisms underlying planar and tissue polarity as well as planar morphogenesis. Furthermore, we discuss the role of physical forces in planar morphogenesis and the contribution of tissue polarity to plant organ shape.

  • 27.
    Petersson, Sara V
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Johansson, Annika I
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kowalczyk, Mariusz
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Makoveychuk, Alexander
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Wang, Jean Y
    Department of Biology and Institute for Genome Sciences & Policy, Center for Systems Biology, Duke University, Durham, North Carolina 27708, USA.
    Moritz, Thomas
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Benfey, Philip N
    Department of Biology and Institute for Genome Sciences & Policy, Center for Systems Biology, Duke University, Durham, North Carolina 27708, USA.
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ljung, Karin
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    An auxin gradient and maximum in the arabidopsis root apex shown by high-resolution cell-specific analysis of IAA distribution and synthesis2009In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 21, no 6, p. 1659-1668Article in journal (Refereed)
    Abstract [en]

    Local concentration gradients of the plant growth regulator auxin (indole-3-acetic acid [IAA]) are thought to instruct the positioning of organ primordia and stem cell niches and to direct cell division, expansion, and differentiation. High-resolution measurements of endogenous IAA concentrations in support of the gradient hypothesis are required to substantiate this hypothesis. Here, we introduce fluorescence-activated cell sorting of green fluorescent protein-marked cell types combined with highly sensitive mass spectrometry methods as a novel means for analyses of IAA distribution and metabolism at cellular resolution. Our results reveal the presence of IAA concentration gradients within the Arabidopsis thaliana root tip with a distinct maximum in the organizing quiescent center of the root apex. We also demonstrate that the root apex provides an important source of IAA and that cells of all types display a high synthesis capacity, suggesting a substantial contribution of local biosynthesis to auxin homeostasis in the root tip. Our results indicate that local biosynthesis and polar transport combine to produce auxin gradients and maxima in the root tip.

  • 28.
    Pietra, Stefano
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Auxin paves the way for planar morphogenesis2010In: Cell, ISSN 0092-8674, E-ISSN 1097-4172, Vol. 143, no 1, p. 29-31Article in journal (Refereed)
  • 29.
    Pietra, Stefano
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gustavsson, Anna
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kiefer, Christian
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kalmbach, Lothar
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Hörstedt, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå Core Facility Electron Microscopy, Umeå University.
    Ikeda, Yoshihisa
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Stepanova, Anna N.
    Department of Genetics, North Carolina State University, Raleigh, North Carolina 27695, USA.
    Alonso, Jose M.
    Department of Genetics, North Carolina State University, Raleigh, North Carolina 27695, USA.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Arabidopsis SABRE and CLASP interact to stabilize cell division plane orientation and planar polarity2013In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, p. 2779-Article in journal (Refereed)
    Abstract [en]

    The orientation of cell division and the coordination of cell polarity within the plane of the tissue layer (planar polarity) contribute to shape diverse multicellular organisms. The root of Arabidopsis thaliana displays regularly oriented cell divisions, cell elongation and planar polarity providing a plant model system to study these processes. Here we report that the SABRE protein, which shares similarity with proteins of unknown function throughout eukaryotes, has important roles in orienting cell division and planar polarity. SABRE localizes at the plasma membrane, endomembranes, mitotic spindle and cell plate. SABRE stabilizes the orientation of CLASP-labelled preprophase band microtubules predicting the cell division plane, and of cortical microtubules driving cell elongation. During planar polarity establishment, sabre is epistatic to clasp at directing polar membrane domains of Rho-of-plant GTPases. Our findings mechanistically link SABRE to CLASP-dependent microtubule organization, shedding new light on the function of SABRE-related proteins in eukaryotes.

  • 30.
    Pietra, Stefano
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Lang, Patricia
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Max Planck Institute for Developmental Biology, Department of Molecular Biology, Tübingen, Germany.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Institute of Biochemistry and Biology, Plant Physiology, University of Potsdam, Germany.
    SABRE is required for stabilization of root hair patterning in Arabidopsis thaliana2015In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 153, no 3, p. 440-453Article in journal (Refereed)
    Abstract [en]

    Patterned differentiation of distinct cell types is essential for the development of multicellular organisms. The root epidermis of Arabidopsis thaliana is composed of alternating files of root hair and non-hair cells and represents a model system for studying the control of cell-fate acquisition. Epidermal cell fate is regulated by a network of genes that translate positional information from the underlying cortical cell layer into a specific pattern of differentiated cells. While much is known about the genes of this network, new players continue to be discovered. Here we show that the SABRE (SAB) gene, known to mediate microtubule organization, anisotropic cell growth and planar polarity, has an effect on root epidermal hair cell patterning. Loss of SAB function results in ectopic root hair formation and destabilizes the expression of cell fate and differentiation markers in the root epidermis, including expression of the WEREWOLF (WER) and GLABRA2 (GL2) genes. Double mutant analysis reveal that wer and caprice (cpc) mutants, defective in core components of the epidermal patterning pathway, genetically interact with sab. This suggests that SAB may act on epidermal patterning upstream of WER and CPC. Hence, we provide evidence for a role of SAB in root epidermal patterning by affecting cell-fate stabilization. Our work opens the door for future studies addressing SAB-dependent functions of the cytoskeleton during root epidermal patterning.

  • 31. Poxson, David J.
    et al.
    Karady, Michal
    Gabrielsson, Roger
    Alkattan, Aziz Y.
    Gustavsson, Anna
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Doyle, Siamsa M.
    Robert, Stephanie
    Ljung, Karin
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, 14476 Potsdam, Golm, Germany.
    Simon, Daniel T.
    Berggren, Magnus
    Regulating plant physiology with organic electronics2017In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 114, no 18, p. 4597-4602Article in journal (Refereed)
    Abstract [en]

    The organic electronic ion pump (OEIP) provides flow-free and accurate delivery of small signaling compounds at high spatio-temporal resolution. To date, the application of OEIPs has been limited to delivery of nonaromatic molecules to mammalian systems, particularly for neuroscience applications. However, many long-standing questions in plant biology remain unanswered due to a lack of technology that precisely delivers plant hormones, based on cyclic alkanes or aromatic structures, to regulate plant physiology. Here, we report the employment of OEIPs for the delivery of the plant hormone auxin to induce differential concentration gradients and modulate plant physiology. We fabricated OEIP devices based on a synthesized dendritic polyelectrolyte that enables electrophoretic transport of aromatic substances. Delivery of auxin to transgenic Arabidopsis thaliana seedlings in vivo was monitored in real time via dynamic fluorescent auxin-response reporters and induced physiological responses in roots. Our results provide a starting point for technologies enabling direct, rapid, and dynamic electronic interaction with the biochemical regulation systems of plants.

  • 32. Singh, Sunil
    et al.
    Fischer, Urs
    Singh, Manoj
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Marchant, Alan
    Insight into the early steps of root hair formation revealed by the procuste1 cellulose synthase mutant of Arabidopsis thaliana.2008In: BMC Plant Biol, ISSN 1471-2229, Vol. 8, no 1, p. 57-Article in journal (Refereed)
    Abstract [en]

    Background

    Formation of plant root hairs originating from epidermal cells involves selection of a polar initiation site and production of an initial hair bulge which requires local cell wall loosening. In Arabidopsis the polar initiation site is located towards the basal end of epidermal cells. However little is currently understood about the mechanism for the selection of the hair initiation site or the mechanism by which localised hair outgrowth is achieved. The Arabidopsis procuste1 (prc1-1) cellulose synthase mutant was studied in order to investigate the role of the cell wall loosening during the early stages of hair formation.

    Results

    The prc1-1 mutant exhibits uncontrolled, preferential bulging of trichoblast cells coupled with mislocalised hair positioning. Combining the prc1-1 mutant with root hair defective6-1 (rhd6-1), which on its own is almost completely devoid of root hairs results in a significant restoration of root hair formation. The pEXPANSIN7::GFP (pEXP7::GFP) marker which is specifically expressed in trichoblast cell files of wild-type roots, is absent in the rhd6-1 mutant. However, pEXP7::GFP expression in the rhd6-1/prc1-1 double mutant is restored in a subset of epidermal cells which have either formed a root hair or exhibit a bulged phenotype consistent with a function for EXP7 during the early stages of hair formation.

    Conclusion

    These results show that RHD6 acts upstream of the normal cell wall loosening event which involves EXP7 expression and that in the absence of a functional RHD6 the loosening and accompanying EXP7 expression is blocked. In the prc1-1 mutant background, the requirement for RHD6 during hair initiation is reduced which may result from a weaker cell wall structure mimicking the cell wall loosening events during hair formation.

  • 33.
    Stanislas, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Boutte, Yohann
    Sterol Dynamics During Endocytic Trafficking in Arabidopsis2014In: PLANT ENDOSOMES: METHODS AND PROTOCOLS, Humana Press, 2014, p. 13-29Chapter in book (Refereed)
    Abstract [en]

    Sterols are lipids found in membranes of eukaryotic cells. Functions of sterols have been demonstrated for various cellular processes including endocytic trafficking in animal, fungal, and plant cells. The ability to visualize sterols at the subcellular level is crucial to understand sterol distribution and function during endocytic trafficking. In plant cells, the polyene antibiotic filipin is the most extensively used tool for the specific detection of fluorescently labeled 3-beta-hydroxysterols in situ. Filipin can to some extent be used to track sterol internalization in live cells, but this application is limited, due to the inhibitory effects filipin exerts on sterol-dependent endocytosis. Nevertheless, filipin-sterol labeling can be performed on aldehyde-fixed cells which allows for sterol detection in endocytic compartments. This approach can combine studies correlating sterol distribution with experimental manipulations of endocytic trafficking pathways. Here, we describe step-by-step protocols and troubleshooting for procedures on live and fixed cells to visualize sterols during endocytic trafficking. We also provide a detailed discussion of advantages and limitations of both methods. Moreover, we illustrate the use of the endocytic recycling inhibitor brefeldin A and a genetically modified version of one of its target molecules for studying endocytic sterol trafficking.

  • 34.
    Stanislas, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Univ Potsdam, Inst Biochem & Biol, Plant Physiol, DE-14476 Potsdam, Germany.
    Huser, Anke
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Barbosa, Ines C. R.
    Kiefer, Christian S.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Brackmann, Klaus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Pietra, Stefano
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gustavsson, Anna
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Zourelidou, Melina
    Schwechheimer, Claus
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Univ Potsdam, Inst Biochem & Biol, Plant Physiol, DE-14476 Potsdam, Germany.
    Arabidopsis D6PK is a lipid domain-dependent mediator of root epidermal planar polarity2015In: Nature Plants, ISSN 2055-026X, Vol. 1, article id 15162Article in journal (Refereed)
    Abstract [en]

    Development of diverse multicellular organisms relies on coordination of single-cell polarities within the plane of the tissue layer (planar polarity). Cell polarity often involves plasma membrane heterogeneity generated by accumulation of specific lipids and proteins into membrane subdomains. Coordinated hair positioning along Arabidopsis root epidermal cells provides a planar polarity model in plants, but knowledge about the functions of proteo-lipid domains in planar polarity signalling remains limited. Here we show that Rho-of-plant (ROP) 2 and 6, phosphatidylinositol-4-phosphate 5-kinase 3 (PIP5K3), DYNAMIN-RELATED PROTEIN (DRP) 1A and DRP2B accumulate in a sterol-enriched, polar membrane domain during root hair initiation. DRP1A, DRP2B, PIP5K3 and sterols are required for planar polarity and the AGCVIII kinase D6 PROTEIN KINASE (D6PK) is a modulator of this process. D6PK undergoes phosphatidylinositol-4,5-bisphosphate- and sterol-dependent basal-to-planar polarity switching into the polar, lipid-enriched domain just before hair formation, unravelling lipid-dependent D6PK localization during late planar polarity signalling.

  • 35.
    Villarejo, Arsenio
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Burén, Stefan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Larsson, Susanne
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Déjardin, Annabelle
    Unité d'Amélioration, de Génétique et de Physiologie Forestières, INRA, BP 20619 Ardon, F-45166 Olivet Cedex, France.
    Monné, Magnus
    Department of Biochemistry and Biophysics, Arrhenius Laboratory, Stockholm University.
    Rudhe, Charlotta
    Department of Biochemistry and Biophysics, Arrhenius Laboratory, Stockholm University.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Jansson, Stefan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Lerouge, Patrice
    University of Rouen, Mont Saint Aignan, France.
    Rolland, Norbert
    Université Joseph Fourier, Grenoble, France.
    von Heijne, Gunnar
    Department of Biochemistry and Biophysics, Arrhenius Laboratory, Stockholm University.
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bako, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Evidence for a protein transported through the secretory pathway en route to the higher plant chloroplast.2005In: Nature Cell Biology, ISSN 1465-7392, Vol. 7, no 12, p. 1224-31Article in journal (Refereed)
    Abstract [en]

    In contrast to animal and fungal cells, green plant cells contain one or multiple chloroplasts, the organelle(s) in which photosynthetic reactions take place. Chloroplasts are believed to have originated from an endosymbiotic event and contain DNA that codes for some of their proteins. Most chloroplast proteins are encoded by the nuclear genome and imported with the help of sorting signals that are intrinsic parts of the polypeptides. Here, we show that a chloroplast-located protein in higher plants takes an alternative route through the secretory pathway, and becomes N-glycosylated before entering the chloroplast.

  • 36.
    Viotti, Corrado
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). University of Heidelberg, Germany.
    Krüger, Falco
    Neubert, Christoph
    Fink, Fabian
    Lupanga, Upendo
    Krebs, Melanie
    Scheuring, David
    Hemsley, Piers A.
    Boutté, Yohann
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Frescatada-Rosa, Márcia
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Wolfenstetter, Susanne
    Sauer, Norbert
    Hillmer, Stefan
    Grebe, Marcus
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Schumacher, Karin
    The Endoplasmic Reticulum Is the Main Membrane Source for Biogenesis of the Lytic Vacuole in Arabidopsis2013In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 25, no 9, p. 3434-3449Article in journal (Refereed)
    Abstract [en]

    Vacuoles are multifunctional organelles essential for the sessile lifestyle of plants. Despite their central functions in cell growth, storage, and detoxification, knowledge about mechanisms underlying their biogenesis and associated protein trafficking pathways remains limited. Here, we show that in meristematic cells of the Arabidopsis thaliana root, biogenesis of vacuoles as well as the trafficking of sterols and of two major tonoplast proteins, the vacuolar H+-pyrophosphatase and the vacuolar H+-adenosinetriphosphatase, occurs independently of endoplasmic reticulum (ER)-Golgi and post-Golgi trafficking. Instead, both pumps are found in provacuoles that structurally resemble autophagosomes but are not formed by the core autophagy machinery. Taken together, our results suggest that vacuole biogenesis and trafficking of tonoplast proteins and lipids can occur directly from the ER independent of Golgi function.

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