@article{KrupinskiBozorgLarssonetal.2016, author = {Krupinski, Pawel and Bozorg, Behruz and Larsson, Andre and Pietra, Stefano and Grebe, Markus and J{\"o}nsson, Henrik}, title = {A Model Analysis of Mechanisms for Radial Microtubular Patterns at Root Hair Initiation Sites}, series = {Frontiers in plant science}, volume = {7}, journal = {Frontiers in plant science}, publisher = {Frontiers Research Foundation}, address = {Lausanne}, issn = {1664-462X}, doi = {10.3389/fpls.2016.01560}, pages = {12}, year = {2016}, abstract = {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.}, language = {en} } @article{KieferClaesNzayisengaetal.2015, author = {Kiefer, Christian S. and Claes, Andrea R. and Nzayisenga, Jean-Claude and Pietra, Stefano and Stanislas, Thomas and Hueser, Anke and Ikeda, Yoshihisa and Grebe, Markus}, title = {Arabidopsis AIP1-2 restricted by WER-mediated patterning modulates planar polarity}, series = {Development : Company of Biologists}, volume = {142}, journal = {Development : Company of Biologists}, number = {1}, publisher = {Company of Biologists Limited}, address = {Cambridge}, issn = {0950-1991}, doi = {10.1242/dev.111013}, pages = {151 -- 161}, year = {2015}, abstract = {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.}, language = {en} } @article{PietraLangGrebe2015, author = {Pietra, Stefano and Lang, Patricia and Grebe, Markus}, title = {SABRE is required for stabilization of root hair patterning in Arabidopsis thaliana}, series = {Physiologia plantarum}, volume = {153}, journal = {Physiologia plantarum}, number = {3}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0031-9317}, doi = {10.1111/ppl.12257}, pages = {440 -- 453}, year = {2015}, abstract = {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.}, language = {en} } @article{StanislasHuserBarbosaetal.2015, author = {Stanislas, Thomas and Huser, Anke and Barbosa, Ines C. R. and Kiefer, Christian S. and Brackmann, Klaus and Pietra, Stefano and Gustavsson, Anna and Zourelidou, Melina and Schwechheimer, Claus and Grebe, Markus}, title = {Arabidopsis D6PK is a lipid domain-dependent mediator of root epidermal planar polarity}, series = {Nature plants}, volume = {1}, journal = {Nature plants}, number = {11}, publisher = {Nature Publ. Group}, address = {London}, issn = {2055-026X}, doi = {10.1038/NPLANTS.2015.162}, pages = {9}, year = {2015}, abstract = {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.}, language = {en} } @article{PietraLangGrebe2015, author = {Pietra, Stefano and Lang, Patricia and Grebe, Markus}, title = {SABRE is required for stabilization of root hair patterning in Arabidopsis thaliana}, series = {Physiologia Plantarum}, volume = {153}, journal = {Physiologia Plantarum}, number = {3}, doi = {DOI: 10.1111/ppl.12257}, pages = {440 -- 453}, year = {2015}, abstract = {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.}, language = {en} } @article{KieferClaesNzayisengaetal.2015, author = {Kiefer, Christian S. and Claes, Andrea R. and Nzayisenga, Jean-Claude and Pietra, Stefano and Stanislas, Thomas and Ikeda, Yoshihisa and Grebe, Markus}, title = {Arabidopsis AIP1-2 restricted by WER-mediated patterning modulates planar polarity}, series = {Development}, journal = {Development}, number = {142}, doi = {doi: 10.1242/dev.111013}, pages = {151 -- 161}, year = {2015}, abstract = {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.}, language = {en} }