title: A combinatorial TIR1/AFB-Aux/IAA co-receptor system for differential sensing of auxin.
abstract: The plant hormone auxin regulates virtually every aspect of plant growth and development. Auxin acts by binding the F-box protein transport inhibitor response 1 (TIR1) and promotes the degradation of the AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) transcriptional repressors. Here we show that efficient auxin binding requires assembly of an auxin co-receptor complex consisting of TIR1 and an Aux/IAA protein. Heterologous experiments in yeast and quantitative IAA binding assays using purified proteins showed that different combinations of TIR1 and Aux/IAA proteins form co-receptor complexes with a wide range of auxin-binding affinities. Auxin affinity seems to be largely determined by the Aux/IAA. As there are 6 TIR1/AUXIN SIGNALING F-BOX proteins (AFBs) and 29 Aux/IAA proteins in Arabidopsis thaliana, combinatorial interactions may result in many co-receptors with distinct auxin-sensing properties. We also demonstrate that the AFB5-Aux/IAA co-receptor selectively binds the auxinic herbicide picloram. This co-receptor system broadens the effective concentration range of the hormone and may contribute to the complexity of auxin response.
authors.affiliation: Section of Cell and Developmental Biology, University of California-San Diego, La Jolla, California, USA.
authors.forename: Luz Irina A
authors.initials: LI
authors.lastname: Calderón Villalobos
authors.forename: Sarah
authors.initials: S
authors.lastname: Lee
authors.forename: Cesar
authors.initials: C
authors.lastname: De Oliveira
authors.forename: Anthony
authors.initials: A
authors.lastname: Ivetac
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Brandt
authors.forename: Lynne
authors.initials: L
authors.lastname: Armitage
authors.forename: Laura B
authors.initials: LB
authors.lastname: Sheard
authors.forename: Xu
authors.initials: X
authors.lastname: Tan
authors.forename: Geraint
authors.initials: G
authors.lastname: Parry
authors.forename: Haibin
authors.initials: H
authors.lastname: Mao
authors.forename: Ning
authors.initials: N
authors.lastname: Zheng
authors.forename: Richard
authors.initials: R
authors.lastname: Napier
authors.forename: Stefan
authors.initials: S
authors.lastname: Kepinski
authors.forename: Mark
authors.initials: M
authors.lastname: Estelle
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry*; D044783:F-Box Proteins / Q000737:chemistry*; D006540:Herbicides / Q000737:chemistry; D007210:Indoleacetic Acids / Q000737:chemistry*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry*; D010846:Picloram / Q000737:chemistry; D011956:Receptors, Cell Surface / Q000737:chemistry*
chemical_list: C516178:AFB5 protein, Arabidopsis; D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; D044783:F-Box Proteins; D006540:Herbicides; C491592:IAA1 protein, Arabidopsis; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D011956:Receptors, Cell Surface; C501405:TIR1 protein, Arabidopsis; D010846:Picloram