Degradation of Aux/IAA proteins is essential for normal auxin signalling

Plant J. 2000 Mar;21(6):553-62. doi: 10.1046/j.1365-313x.2000.00703.x.


The growth substance auxin mediates many cellular processes, including division, elongation and differentiation. PSIAA6 is a member of the Aux/IAA family of short-lived putative transcriptional regulators that share four conserved domains and whose mRNAs are rapidly induced in the presence of auxin. Here PSIAA6 was shown to serve as a dominant transferable degradation signal when present as a translational fusion with firefly luciferase (LUC), with an in vivo half-life of 13.5 min in transgenic Arabidopsis seedlings. In a transient assay system in tobacco protoplasts using steady-state differences as an indirect measure of protein half-life, LUC fusions with full-length PSIAA6 and IAA1, an Aux/IAA protein from Arabidopsis, resulted in protein accumulations that were 3.5 and 1. 0%, respectively, of that with LUC alone. An N-terminal region spanning conserved domain II of PSIAA6 containing amino acids 18-73 was shown to contain the necessary cis-acting element to confer low protein accumulation onto LUC, while a fusion protein with PSIAA6 amino acids 71-179 had only a slight effect. Single amino acid substitutions of PSIAA6 in conserved domain II, equivalent to those found in two alleles of axr3, a gene that encodes Aux/IAA protein IAA17, resulted in a greater than 50-fold increase in protein accumulation. Thus, the same mutations resulting in an altered auxin response phenotype increase Aux/IAA protein accumulation, providing a direct link between these two processes. In support of this model, transgenic plants engineered to over-express IAA17 have an axr3-like phenotype. Together, these data suggest that rapid degradation of Aux/IAA proteins is necessary for a normal auxin response.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis
  • Arabidopsis Proteins*
  • Electrophoresis, Polyacrylamide Gel
  • Indoleacetic Acids / physiology*
  • Nuclear Proteins / physiology*
  • Plant Proteins / physiology*
  • Plants, Genetically Modified
  • Signal Transduction*
  • Transcription Factors


  • AXR3 protein, Arabidopsis
  • Arabidopsis Proteins
  • Indoleacetic Acids
  • Nuclear Proteins
  • Plant Proteins
  • Transcription Factors