title: The IAA1 protein is encoded by AXR5 and is a substrate of SCF(TIR1).
abstract: Recent studies of auxin response have focused on the functions of three sets of proteins: the auxin (Aux) response factors (ARFs), the Aux/IAAs, and the F-box protein TIR1. The ARF proteins bind DNA and directly activate or repress transcription of target genes while the Aux/IAA proteins repress ARF function. TIR1 is part of a ubiquitin protein ligase required for degradation of Aux/IAA proteins. Here we report the isolation and characterization of a novel mutant of Arabidopsis called axr5-1. Mutant plants are resistant to auxin and display a variety of auxin-related growth defects including defects in root and shoot tropisms. Further, the axr5-1 mutation results in a decrease in auxin-regulated transcription. The molecular cloning of AXR5 revealed that the gene encodes the IAA1 protein, a member of the Aux/IAA family of proteins. AXR5 is expressed throughout plant development consistent with the pleiotropic mutant phenotype. The axr5-1 mutation results in an amino acid substitution in conserved domain II of the protein, similar to gain-of-function mutations recovered in other members of this gene family. Biochemical studies show that IAA1/AXR5 interacts with TIR1 in an auxin-dependent manner. The mutation prevents this interaction suggesting that the mutant phenotype is caused by the accumulation of IAA1/AXR5. Our results provide further support for a model in which most members of the Aux/IAA family are targeted for degradation by SCFTIR1 in response to auxin.
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Yang
authors.forename: Sungsu
authors.initials: S
authors.lastname: Lee
authors.forename: Jai-Hyun
authors.initials: JH
authors.lastname: So
authors.forename: Suni
authors.initials: S
authors.lastname: Dharmasiri
authors.forename: Nihal
authors.initials: N
authors.lastname: Dharmasiri
authors.forename: Lei
authors.initials: L
authors.lastname: Ge
authors.forename: Carolyn
authors.initials: C
authors.lastname: Jensen
authors.forename: Roger
authors.initials: R
authors.lastname: Hangarter
authors.forename: Lawrence
authors.initials: L
authors.lastname: Hobbie
authors.forename: Mark
authors.initials: M
authors.lastname: Estelle
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000494:pharmacology; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; C491592:IAA1 protein, Arabidopsis; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D044843:SKP Cullin F-Box Protein Ligases