ROOT HAIRS Cloe de Luxn Hernndez PCDU Seminar D EFINITION Long tubular-shaped outgrowths from root epidermal cells Increase root surface area and diameter Grierson, C; Nielsen, E; Ketelaar, T and Schiefelbein, J. The Arabidopsis Book Root hairs. American Society of Plant Biologists (2014) P ATTERN OF EPIDERMAL CELLS IN THE ROOT Root hair cells and non-hair cells are interspersed. H position: intercelular space between two cortical cells N position: over a single cortical cell Grierson, C; Nielsen, E; Ketelaar, T and Schiefelbein, J. The Arabidopsis Book Root hairs. American Society of Plant Biologists (2014) Cell- cell comunication events are critical for the establishment of cell indentity in the root epidermis. N ATURE OF THE CELL PATTERNING INFORMATION Position-dependent epidermal cell pattern is determined at early stages of epidermal development. Trichoblasts and Atrichoblasts are distinguished before hair outgrowth. Trichoblasts vs Atrichoblasts DivisionHighLow LengthSmallBig Cytoplasmic densityHighLow Rate of vacuolationLowHigh N ATURE OF THE CELL PATTERNING INFORMATION GLABRA 2 (specifical expression in non-hair cells) fused to GUS reporter gene N position H position Grierson, C; Nielsen, E; Ketelaar, T and Schiefelbein, J. The Arabidopsis Book Root hairs. American Society of Plant Biologists (2014) N ATURE OF THE CELL PATTERNING INFORMATION GLABRA 2 (specifical expression in non-hair cells) fused to GFP Epidermial cell pattern initiated during embryogenesis External application of auxin and ethylene induces root hair cell differentiation in cells in both H and N position. Grierson, C; Nielsen, E; Ketelaar, T and Schiefelbein, J. The Arabidopsis Book Root hairs. American Society of Plant Biologists (2014) R OOT HAIR FORMATION Two main steps: Root hair initiation Root hair tip growth Small area of the cell wall loosens to form a swelling Hair grows by targeted secretion Grierson, C; Nielsen, E; Ketelaar, T and Schiefelbein, J. The Arabidopsis Book Root hairs. American Society of Plant Biologists (2014) R OOT HAIR INITIATION Rop accumulation at the apical plasma membrane domains in the tip of root hairs assisted by receptor-like kinase FERONIA. pH drop that leads to the activation of expansins. ER condensation and actin accumulation. Grierson, C; Nielsen, E; Ketelaar, T and Schiefelbein, J. The Arabidopsis Book Root hairs. American Society of Plant Biologists (2014) R OOT HAIR TIP GROWTH Extremely polarized type of cell expansion that results in the formation of a tubular cell. Sustained by exocytosis of vesicles in the root hair apex. Vesicles produced by smooth and rough ER and Golgi complexes. Cell wall materials accumulation ROPs cell wall polysaccharides and cell wall (glyco)proteins R OOT HAIR TIP GROWTH High polarization of the citoplasm. Tip growth unit: all celular constituents that support tip-growth Delivery of new vesicles is assisted by cytoplasmic streaming Ketelaar, T. The actin cytoskeleton in root hairs: all is fine at the tip. Current opinion in Plant Biology (2013) 16: 1-8 C ALCIUM IN TIP GROWTH Root hairs of 5-10 m long experiment an increase of Ca2+ concentration from about 200 nM to at least 1 M. Calcium gradient at the tip of the hair controls direction of growth (Facilitates fusion of exocytotic vesicles with PM) ROP RHD2 (NADPHox) ROS activation of calcium channels Tip focused Ca2+ gradient remains throughout tip growth Related to ABP A CTIN IN TIP GROWTH Functions as a backbone for cytoplasmic streaming. Organizes the cytoplasm of the subapical region G-actin F-actin POLYMERIZATION DEPOLYMERIZATION Actin inhibitors Tip growth Latrunculin B Bulge formation A CTIN IN TIP GROWTH Actin organization is highly polarized. Supports cytoplasmic streaming in the cortical cytoplasm Supports accumulation of cytoplasm in the (sub)apical part Ketelaar, T. The actin cytoskeleton in root hairs: all is fine at the tip. Current opinion in Plant Biology (2013) 16: 1-8 A CTIN IN TIP GROWTH Actin plays a role in determining root hair width [Actin inhibitors] A CTIN BINDING PROTEINS (ABP S ) Play an important role in determining the higher-order organization of the actin cytoskeleton. Its activity is modulated by the tip-focused Ca2+ gradient Several groups: Actin nucleating proteins Actin depolymerizers Actin bundling proteins Motor proteins A CTIN NUCLEATING PROTEINS Arp2/3 complex: In some mutants: wavy, swollen and branching root hairs with reduced length No important role in actin organization during root hair growth Arp2/3 complex A CTIN NUCLEATING PROTEINS Formins: 2 classes Accumulation of FH8 causes an accumulation of F-actin in growing root hair tips and defects in actin organization and growth defects such as growth reduction, tip swelling, wavyness and branching Highly related to profilins. Overexpression of PFN1 causes the formation of root hairs that are twice as long as root hairs in WT. Actin trimer Formin dimer A CTIN DEPOLYMERIZERS Actin depolymerizing factor (ADF) : increases actin turnover by severing actin filaments and increasing the dissociation rate from their minus ends. Its activity is enhanced by high [Ca2+] Enhancement of ADF activity plays a role in fine F-actin formation. Actin Interacting Protein 1 (AIP1): enhances ADF activity Reduced expression: growth velocity decreases Increased expression: root hair tip swelling and inhibition of root hair growth A CTIN BUNDLING PROTEINS Villins: 3 activities: Ca2+/calmodulin-activated actin severing and capping Actin filament bundling VILLIN4 gene mutation: finer actin organization, lower elongation rate, and decreased cytoplasmic streaming rate. (Villins implicated in actin bundling in root hairs) Ca2+ dependent actin severing and capping activities of villin are involved in the regulation of actin dynamics in the apical area of pollen tubes. (Likely same role in root hairs) M OTOR PROTEINS Myosin XI: function in actin-dependent organelle trafficking and actin-mediated cytoplasmic restructuring. Mutations in Myosin XI genes: root hair growth reduction and altered actin organization Ca2+ dependent inhibition (reduced cytoplasmic streaming velocities) P OLARIZED M EMBRANE TRAFFICKING IN R OOT H AIRS Plant Rab GTPases control this mechanism TGN membranes Secretory vesicles Prisca Campanoni, P. and Blatt M.R. Membrane trafficking and polar growth in root hairs and pollen tubes. Journal of Experimental Botany (2007) Vol. 58, No. 1, pp. 6574 P OLARIZED M EMBRANE TRAFFICKING IN R OOT H AIRS Caffeine treatment: modulates tip-focused calcium gradient Yariv reagent treatment: precipitation of arabinogalactan proteins Inhibit elongations of pollen tubes Secretion and growth may be uncoupled More membrane is added to the plasma membrane than is required for growth. (Excess membrane being retrieved by endocytosis) P OLARIZED M EMBRANE TRAFFICKING IN R OOT H AIRS Exocytotic pathway - Complete fusin with the PM - Kiss and run mechanism Recycling pathway Degradation pathway Recycling pathway Clathrin-coated vesicle Uncoated vesicle Secretory vesicle MVB Vacuole C ESSATION OF T IP G ROWTH Tip Growth is sustained by auxin provided by neighbouring non-hair cells Auxin transport Root tip growing End of growth: Production of a symmetrical dome-shaped tip Dispersal of the citoplasm at the tip Enlargement of the vacuole into the dome Lost of Rop protein, calcium gradient and calcium cannel activity at the tip ROOT HAIRS AND NUTRIENT ACQUISITION Root hairs facilitate the uptake of nutrients from the soil. Root hair development is strongly regulated by nutrient concentration (P, Fe, Mn and Zn) [P]1M1M1000 M Root hair densityHighLow R EFERENCES Grierson, C; Nielsen, E; Ketelaar, T and Schiefelbein, J. The Arabidopsis Book Root hairs. American Society of Plant Biologists (2014) Prisca Campanoni, P. and Blatt M.R. Membrane trafficking and polar growth in root hairs and pollen tubes. Journal of Experimental Botany (2007) Vol. 58, No. 1, pp. 6574 Ketelaar, T. The actin cytoskeleton in root hairs: all is fine at the tip. Current opinion in Plant Biology (2013) 16: 1-8 Schneider, S.W. Kiss and run mechanism in exocytosis. The Journal of Membrane Biology (2001) 181: Ovecka, M; Lang, I; Baluska, F; Ismail, A; Illes, P; Lichtscheidl, I.K. Endocytosis and vesicle trafficking during tip growth of root hairs. Protoplasma (2005) 226: