Acceleration of Aux/IAA proteolysis is specific for auxin and independent of AXR1

Plant J. 2003 Aug;35(3):285-94. doi: 10.1046/j.1365-313x.2003.01801.x.


Aux/IAA proteins are short-lived transcriptional regulators involved in auxin signaling. Using Aux/IAA luciferase (LUC) fusion proteins expressed in Arabidopsis thaliana, we previously showed that rapid degradation of these proteins requires conserved Aux/IAA domain II and that exogenous auxin accelerates their degradation. To further examine auxin-mediated increases in proteolysis, the degradation of two other LUC fusion proteins, a non-cleavable ubiquitin LUC fusion (UB1-72::LUC) and SAUR15::LUC was determined in vivo in seedlings. Their half-lives were 20 +/- 4 and 104 +/- 10 min, respectively. SAUR15::LUC half-life was not affected by pre-incubation with 2,4-D. Auxin did not have an equivalent effect on UB(1-72)::LUC steady-state levels as compared to PsIAA6:LUC. LUC fused to an Aux/IAA domain II degraded more rapidly following auxin application, demonstrating that this region is sufficient for auxin-mediated acceleration of proteolysis. Hormonal cross-talk at the level of Aux/IAA proteolysis was examined. 1-aminocyclopropane-1-carboxylic acid (ACC), benzyladenine (BA), abscisic acid (ABA), and brassinolide (BL) did not affect the degradation rate of IAA1::LUC, and gibberellic acid (GA3) and salicylic acid (SA) did not specifically affect the steady-state levels of Aux/IAA::LUC proteins. An Aux/IAA::LUC transgene was crossed into the auxin resistant-1 (axr1-12) background. In axr1-12, the half-life of PsIAA6(1-73)::LUC increased 4.5-fold, but proteolysis still accelerated in response to exogenous auxin. These data suggest that auxin is the only phytohormone that accelerates Aux/IAA proteolysis, and that this acceleration is specific for Aux/IAA proteins. In addition, AXR1 plays an important role in rapid basal proteolysis of Aux/IAA proteins, but is not required for auxin-mediated acceleration of their degradation.

Publication types

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

MeSH terms

  • Amino Acids, Cyclic / pharmacology
  • Arabidopsis / drug effects
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Endopeptidases / metabolism
  • Indoleacetic Acids / metabolism*
  • Indoleacetic Acids / pharmacology
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Plant Proteins*
  • Plants, Genetically Modified
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Seedlings / drug effects
  • Seedlings / metabolism
  • Signal Transduction
  • Transcription Factors / genetics
  • Transcription Factors / metabolism


  • AXR1 protein, Arabidopsis
  • Amino Acids, Cyclic
  • Arabidopsis Proteins
  • DNA-Binding Proteins
  • IAA1 protein, Arabidopsis
  • IAA1 protein, plant
  • Indoleacetic Acids
  • Nuclear Proteins
  • Plant Proteins
  • Recombinant Fusion Proteins
  • Transcription Factors
  • 1-aminocyclopropane-1-carboxylic acid
  • Endopeptidases