title: Post-transcriptional control of the Arabidopsis auxin efflux carrier EIR1 requires AXR1.
abstract: The auxin efflux carrier EIR1 (also known as AGR and AtPIN2) is a key mediator of the response of Arabidopsis roots to gravity [1,2]. This response is thought to require the establishment of a transient auxin gradient in the root meristem, resulting in differential cell elongation [3]. Recent reports suggest that EIR1 is essential for the asymmetric distribution of auxin in the root meristem [4-7], but the regulatory aspects of this process are still not fully understood. Here, we studied the regulation of EIR1 in Arabidopsis using two reporters: one was a translational fusion that contained the entire EIR1 coding sequence, and the other a transcriptional fusion that had no EIR1 coding sequence. We found that EIR1 is controlled at the post-transcriptional level. The translational fusion was unstable in response to changes in auxin homeostasis, and was destabilized by cycloheximide. In contrast, the protein was stabilized in the axr1-3 mutant, which is auxin resistant and defective in auxin responses such as root gravitropism [8,9]. AXR1 is thought to participate in ubiquitin-mediated control of protein stability [10-12]. The dependence of EIR1 reporter expression on auxin concentrations and AXR1 suggests that auxin transport is regulated through a feedback regulatory loop that affects protein stability in response to auxin.
authors.affiliation: Centre for Applied Genetics, University of Agricultural Sciences, Muthgasse 18, A-1190 Vienna, Austria.
authors.forename: T
authors.initials: T
authors.lastname: Sieberer
authors.forename: G J
authors.initials: GJ
authors.lastname: Seifert
authors.forename: M T
authors.initials: MT
authors.lastname: Hauser
authors.forename: P
authors.initials: P
authors.lastname: Grisafi
authors.forename: G R
authors.initials: GR
authors.lastname: Fink
authors.forename: C
authors.initials: C
authors.lastname: Luschnig
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D017343:Genes, Plant; D017930:Genes, Reporter / Q000235:genetics*; D006133:Growth Substances; D007150:Immunohistochemistry; D007210:Indoleacetic Acids / Q000378:metabolism*; D026901:Membrane Transport Proteins; D018519:Meristem / Q000033:anatomy & histology / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D006133:Growth Substances; D007210:Indoleacetic Acids; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; C081977:AXR1 protein, Arabidopsis; C117013:AT5G57090 protein, Arabidopsis