Structure-Function Analysis of the Presumptive Arabidopsis Auxin Permease AUX1[W]

Author:

Swarup Ranjan1,Kargul Joanna1,Marchant Alan1,Zadik Daniel1,Rahman Abidur2,Mills Rebecca3,Yemm Anthony14,May Sean1,Williams Lorraine3,Millner Paul5,Tsurumi Seiji2,Moore Ian6,Napier Richard4,Kerr Ian D.7,Bennett Malcolm J.1

Affiliation:

1. School of Biosciences, Sutton Bonington Campus, University of Nottingham, United Kingdom

2. Centre for Support to Research and Education Activities Isotope Division, Kobe University, Kobe, Japan

3. School of Biological Sciences, University of Southampton, United Kingdom

4. Warwick-HRI, University of Warwick, Wellesbourne, United Kingdom

5. School of Biochemistry and Molecular Biology, University of Leeds, Leeds, United Kingdom

6. Plant Sciences, University of Oxford, United Kingdom

7. School of Biomedical Sciences, Queens Medical Centre, University of Nottingham, United Kingdom

Abstract

Abstract We have investigated the subcellular localization, the domain topology, and the amino acid residues that are critical for the function of the presumptive Arabidopsis thaliana auxin influx carrier AUX1. Biochemical fractionation experiments and confocal studies using an N-terminal yellow fluorescent protein (YFP) fusion observed that AUX1 colocalized with plasma membrane (PM) markers. Because of its PM localization, we were able to take advantage of the steep pH gradient that exists across the plant cell PM to investigate AUX1 topology using YFP as a pH-sensitive probe. The YFP-coding sequence was inserted in selected AUX1 hydrophilic loops to orient surface domains on either apoplastic or cytoplasmic faces of the PM based on the absence or presence of YFP fluorescence, respectively. We were able to demonstrate in conjunction with helix prediction programs that AUX1 represents a polytopic membrane protein composed of 11 transmembrane spanning domains. In parallel, a large aux1 allelic series containing null, partial-loss-of-function, and conditional mutations was characterized to identify the functionally important domains and amino acid residues within the AUX1 polypeptide. Whereas almost all partial-loss-of-function and null alleles cluster in the core permease region, the sole conditional allele aux1-7 modifies the function of the external C-terminal domain.

Publisher

Oxford University Press (OUP)

Subject

Cell Biology,Plant Science

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