title: The F-box protein TIR1 is an auxin receptor.
abstract: The plant hormone auxin regulates diverse aspects of plant growth and development. Recent studies indicate that auxin acts by promoting the degradation of the Aux/IAA transcriptional repressors through the action of the ubiquitin protein ligase SCF(TIR1). The nature of the signalling cascade that leads to this effect is not known. However, recent studies indicate that the auxin receptor and other signalling components involved in this response are soluble factors. Using an in vitro pull-down assay, we demonstrate that the interaction between transport inhibitor response 1 (TIR1) and Aux/IAA proteins does not require stable modification of either protein. Instead auxin promotes the Aux/IAA-SCF(TIR1) interaction by binding directly to SCF(TIR1). We further show that the loss of TIR1 and three related F-box proteins eliminates saturable auxin binding in plant extracts. Finally, TIR1 synthesized in insect cells binds Aux/IAA proteins in an auxin-dependent manner. Together, these results indicate that TIR1 is an auxin receptor that mediates Aux/IAA degradation and auxin-regulated transcription.
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
authors.forename: Nihal
authors.initials: N
authors.lastname: Dharmasiri
authors.forename: Sunethra
authors.initials: S
authors.lastname: Dharmasiri
authors.forename: Mark
authors.initials: M
authors.lastname: Estelle
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D044783:F-Box Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D018411:Spodoptera; D013696:Temperature; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D044783:F-Box Proteins; C491592:IAA1 protein, Arabidopsis; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D011956:Receptors, Cell Surface; D012097:Repressor Proteins; C501405:TIR1 protein, Arabidopsis; D044843:SKP Cullin F-Box Protein Ligases