title: A Model Analysis of Mechanisms for Radial Microtubular Patterns at Root Hair Initiation Sites.
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.
authors.affiliation: Computational Biology and Biological Physics, Department of Astronomy and Theoretical Physics, Lund University Lund, Sweden.
authors.forename: Pawel
authors.initials: P
authors.lastname: Krupinski
authors.affiliation: Computational Biology and Biological Physics, Department of Astronomy and Theoretical Physics, Lund University Lund, Sweden.
authors.forename: Behruz
authors.initials: B
authors.lastname: Bozorg
authors.affiliation: Computational Biology and Biological Physics, Department of Astronomy and Theoretical Physics, Lund University Lund, Sweden.
authors.forename: André
authors.initials: A
authors.lastname: Larsson
authors.affiliation: Department of Plant Physiology, Umeå Plant Science Centre, Umeå University Umeå, Sweden.
authors.forename: Stefano
authors.initials: S
authors.lastname: Pietra
authors.affiliation: Department of Plant Physiology, Umeå Plant Science Centre, Umeå UniversityUmeå, Sweden; Institute of Biochemistry and Biology, Plant Physiology, University of PotsdamPotsdam, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Grebe
authors.affiliation: Computational Biology and Biological Physics, Department of Astronomy and Theoretical Physics, Lund UniversityLund, Sweden; Sainsbury Laboratory, University of CambridgeCambridge, UK; Department of Applied Mathematics and Theoretical Physics, University of CambridgeCambridge, UK.
authors.forename: Henrik
authors.initials: H
authors.lastname: Jönsson
keywords: cellulose fibers; composite material; computational morphodynamics; finite element modeling; microtubules; plant cell wall; root hair initiation