1. Department of Cell and Developmental Biology, and
2. Computational Biology Group, John Innes Centre, Norwich NR4 7UH, UK
3. Department of Plant Physiology, Charles University, Vinicna 5, Prague 2, 128 00, Czech Republic
4. Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Rozvojova 135, Prague 6, 165 02, Czech Republic
5. †Present addresses: École Pratique des Hautes Études, 46 rue de Lille, 75007 Paris, France (R.J.C.); School of Applied Sciences, Ellison Building, University of Northumbria, Newcastle upon Tyne NE1 8ST, UK (M.C.D); Department of Molecular, Cellular and Developmental Biology, PO Box 208104, Yale University, 266 Whitney Avenue, New Haven, Connecticut 06520-8104, USA (S.D.)

Correspondence to: Liam Dolan¹ Correspondence and requests for materials should be addressed to L.D. (Email: liam.dolan@bbsrc.ac.uk).

Abstract

Root hairs are cellular protuberances extending from the root surface into the soil; there they provide access to immobile inorganic ions such as phosphate, which are essential for growth¹. Their cylindrical shape results from a polarized mechanism of cell expansion called tip growth in which elongation is restricted to a small area at the surface of the hair-forming cell (trichoblast) tip^{2, 3, 4}. Here we identify proteins that spatially control the sites at which cell growth occurs by isolating Arabidopsis mutants (scn1) that develop ectopic sites of growth on trichoblasts. We cloned SCN1 and showed that SCN1 is a RhoGTPase GDP dissociation inhibitor (RhoGDI) that spatially restricts the sites of growth to a single point on the trichoblast. We showed previously that localized production of reactive oxygen species by RHD2/AtrbohC NADPH oxidase is required for hair growth⁵; here we show that SCN1/AtrhoGDI1 is a component of the mechanism that focuses RHD2/AtrbohC-catalysed production of reactive oxygen species to hair tips during wild-type development. We propose that the spatial organization of growth in plant cells requires the local RhoGDI-regulated activation of the RHD2/AtrbohC NADPH oxidase.

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