The IAA1 protein is encoded by AXR5 and is a substrate of SCF(TIR1)

Plant J. 2004 Dec;40(5):772-82. doi: 10.1111/j.1365-313X.2004.02254.x.

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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Arabidopsis / drug effects
  • Arabidopsis / genetics*
  • Arabidopsis / growth & development
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics*
  • Arabidopsis Proteins / metabolism
  • DNA-Binding Proteins / genetics*
  • DNA-Binding Proteins / metabolism
  • Gene Expression Regulation, Plant
  • Indoleacetic Acids / pharmacology
  • Mutation
  • Nuclear Proteins / genetics*
  • Nuclear Proteins / metabolism
  • Phenotype
  • SKP Cullin F-Box Protein Ligases / metabolism*

Substances

  • Arabidopsis Proteins
  • DNA-Binding Proteins
  • IAA1 protein, Arabidopsis
  • Indoleacetic Acids
  • Nuclear Proteins
  • SKP Cullin F-Box Protein Ligases