ROOT ULTRAVIOLET B-SENSITIVE1/WEAK AUXIN RESPONSE3 Is Essential for Polar Auxin Transport in Arabidopsis

Hong Yu,Jerry Cohen,Michael Karampelias,Ranjan Swarup,Wendy Ann Peer,Mark Estelle,Angus Murphy,Songqing Ye,Lei Ge,Stephanie Robert,Jirí Friml

doi:10.1104/pp.113.217018

Abstract

The phytohormone auxin regulates virtually every aspect of plant development. To identify new genes involved in auxin activity, a genetic screen was performed for Arabidopsis (Arabidopsis thaliana) mutants with altered expression of the auxin-responsive reporter DR5rev:GFP. One of the mutants recovered in the screen, designated as weak auxin response3 (wxr3), exhibits much lower DR5rev:GFP expression when treated with the synthetic auxin 2,4-dichlorophenoxyacetic acid and displays severe defects in root development. The wxr3 mutant decreases polar auxin transport and results in a disruption of the asymmetric auxin distribution. The levels of the auxin transporters AUXIN1 and PIN-FORMED are dramatically reduced in the wxr3 root tip. Molecular analyses demonstrate that WXR3 is ROOT ULTRAVIOLET B-SENSITIVE1 (RUS1), a member of the conserved Domain of Unknown Function647 protein family found in diverse eukaryotic organisms. Our data suggest that RUS1/WXR3 plays an essential role in the regulation of polar auxin transport by maintaining the proper level of auxin transporters on the plasma membrane.

Highlights

IntroductionOne of the mutants recovered in the screen, designated as weak auxin response (wxr3), exhibits much lower DR5rev:GFP expression when treated with the synthetic auxin 2,4-dichlorophenoxyacetic acid and displays severe defects in root development
Howard Hughes Medical Institute and Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California 92093 (H.Y., M.E.); Swedish University of Agricultural Sciences/Umeå Plant Science Center, Department of Forest Genetics and Plant Physiology, 90183 Umea, Sweden (S.R.); Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland 20742 (W.A.P., A.M.); School of Biosciences and Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, United Kingdom (R.S.); Department of Horticultural Science and Microbial and Plant Genomics Institute, University of Minnesota, St
We present data showing that the wxr3 mutant exhibits dramatically reduced levels of auxin transporters, which leads to a reduction in polar auxin transport and defects in the auxin response

Summary

Introduction

One of the mutants recovered in the screen, designated as weak auxin response (wxr3), exhibits much lower DR5rev:GFP expression when treated with the synthetic auxin 2,4-dichlorophenoxyacetic acid and displays severe defects in root development. Our data suggest that RUS1/WXR3 plays an essential role in the regulation of polar auxin transport by maintaining the proper level of auxin transporters on the plasma membrane. The plant hormone indole-3-acetic acid (IAA) is the most important natural auxin It regulates virtually every aspect of plant development, including embryogenesis, root initiation, lateral root development, tropic responses, leaf formation, stem elongation, and fruit development (Möller and Weijers, 2009; Sundberg and Østergaard, 2009; Takahashi et al, 2009; Overvoorde et al, 2010; Scarpella et al, 2010; Vernoux et al, 2010). PINOID, a Ser/Thr kinase, phosphorylates PIN proteins and is crucial for apical PIN delivery; while protein phosphatase 2A (PP2A) functions antagonistically to PINOID (Friml et al, 2004; Michniewicz et al, 2007; Zhang et al, 2010)

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