Root Hairs

Authors: Grierson, Claire, Nielsen, Erik, Ketelaarc, Tijs, and ​Schiefelbein, John

Source: The Arabidopsis Book, 2014(12)

Published By: The American Society of Plant Biologists

URL: https://doi.org/10.1199/tab.0172

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The Arabidopsis Book

© 2014 American Society of Plant Biologists

First published on June 25, 2014: e0172. doi: 10.1199/tab.0172

This is an updated version of a chapter originally published on April 4, 2002, e0060. doi:10.1199/tab.0060

Root Hairs

Claire Griersona, Erik Nielsenb, Tijs Ketelaarc, and John Schiefelbein

d,1

a

School of Biological Sciences, University of Bristol, Bristol, UK BS8 1UG.

b

Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA 48109.

c

Laboratory of Cell Biology, Wageningen University, 6708 PB Wageningen, The Netherlands.

d

Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA 48109.

1

Address correspondence to schiefel@umich.edu

Roots hairs are cylindrical extensions of root epidermal cells that are important for acquisition of nutrients, microbe interac- ​tions, and plant anchorage. The molecular mechanisms involved in the specification, differentiation, and physiology of root ​hairs in Arabidopsis are reviewed here. Root hair specification in Arabidopsis is determined by position-dependent signaling ​and molecular feedback loops causing differential accumulation of a WD-bHLH-Myb transcriptional complex. The initiation of ​root hairs is dependent on the RHD6 bHLH gene family and auxin to define the site of outgrowth. Root hair elongation relies ​on polarized cell expansion at the growing tip, which involves multiple integrated processes including cell secretion, endo- ​membrane trafficking, cytoskeletal organization, and cell wall modifications. The study of root hair biology in Arabidopsis has ​provided a model cell type for insights into many aspects of plant development and cell biology.

INTRODUCTION

Root hairs are long tubular-shaped outgrowths from root epider- ​mal cells. In Arabidopsis, root hairs are approximately 10 μm in ​diameter and can grow to be 1 mm or more in length (Figure 1). ​Because they vastly increase the root surface area and effec- ​tively increase the root diameter, root hairs are generally thought ​to aid plants in nutrient acquisition, anchorage, and microbe inter- ​actions (Hofer, 1991).

Root hairs in Arabidopsis have attracted a great deal of at- ​tention from plant biologists because they provide numerous ​advantages for basic studies of development, cell biology, and ​physiology (Schiefelbein and Somerville, 1990). The presence ​of root hairs at the surface of the root and away from the plant ​body means that they are easily visualized and accessible to a ​variety of experimental manipulations. Further, the lack of a cu- ​ticle layer allows physical and chemical probes to be applied with ​ease. Root hairs grow rapidly, at a rate of more than 1 μm/min, ​which facilitates studies of cell expansion. Perhaps most impor- ​tantly, root hairs are not essential for plant viability, which permits ​the recovery and analysis of all types of mutants that alter root ​hair development and function. Also, root hairs become visible ​on seedling roots shortly after seed germination, which enables ​genetic screens and physiological tests to be performed rapidly ​with large numbers of individuals grown on defined media in Petri ​dishes (Figure 2). Finally, the development of root hairs (and their

Figure 1. Scanning electron micrograph of a root hair cell. The hair pro- ​duced by this cell is approximately 1/3 of its final length.

resident epidermal cells) occurs in a predictable and progressive ​manner in cells organized in files emanating from the root tip (Fig- ​ure 3). This provides the opportunity for detailed analysis of the ​cellular changes that occur during the entire process of root hair ​formation.

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