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Gene Review


Arabidopsis thaliana

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High impact information on TIR1

  • The transcription activator NAC1, a member of the NAM/CUC family of transcription factors, functions downstream of TIR1 to transduce the auxin signal for lateral root development [1].
  • Mutations in either ASK1 or TIR1 result in decreased auxin response [2].
  • Further, overexpression of TIR1 promotes auxin response suggesting that SCFTIR1 is limiting for the response [2].
  • Further, mutations in TIR1 display a synergistic interaction with mutations in AXR1, suggesting that the two genes function in overlapping pathways [3].
  • The TIR1 protein contains a series of leucine-rich repeats and a recently identified motif called an F box [3].

Biological context of TIR1

  • The role of TIR1 in ubiquitination and regulated degradation of Aux/IAA transcription factors has been recognized for some years, but recent results have shown that TIR1 itself is also the binding site for auxin [4].
  • At5g49980 is previously uncharacterized and encodes auxin signaling F-box protein 5, one of five homologs of TIR1 in the Arabidopsis genome [5].
  • The eta3 mutation interacts synergistically with tir1-1 to strongly enhance all aspects of the tir1 mutant phenotype, including auxin inhibition of root growth, lateral root development, hypocotyl elongation at high temperature, and apical dominance [6].

Associations of TIR1 with chemical compounds

  • 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 [7].
  • TIR1 is the recognition component of the Skp1-cullin-F-box complex associated with the ubiquitin-proteasome pathway involved in auxin signaling and has recently been shown to be a receptor for IAA and 2,4-D [5].

Physical interactions of TIR1

  • Biochemical studies show that IAA1/AXR5 interacts with TIR1 in an auxin-dependent manner [7].
  • Correspondingly, all TIR1/AFB proteins interact with BDL, and BDL is stabilized in triple mutant plants [8].

Other interactions of TIR1

  • Together, these results indicate that TIR1 is an auxin receptor that mediates Aux/IAA degradation and auxin-regulated transcription [9].
  • TIR1 is part of a ubiquitin protein ligase required for degradation of Aux/IAA proteins [7].
  • The affinity and specificity of TIR1 match properties anticipated of a nuclear auxin receptor and we look at how they compare with the properties of ABP1 [4].


  1. SINAT5 promotes ubiquitin-related degradation of NAC1 to attenuate auxin signals. Xie, Q., Guo, H.S., Dallman, G., Fang, S., Weissman, A.M., Chua, N.H. Nature (2002) [Pubmed]
  2. Identification of an SCF ubiquitin-ligase complex required for auxin response in Arabidopsis thaliana. Gray, W.M., del Pozo, J.C., Walker, L., Hobbie, L., Risseeuw, E., Banks, T., Crosby, W.L., Yang, M., Ma, H., Estelle, M. Genes Dev. (1999) [Pubmed]
  3. The TIR1 protein of Arabidopsis functions in auxin response and is related to human SKP2 and yeast grr1p. Ruegger, M., Dewey, E., Gray, W.M., Hobbie, L., Turner, J., Estelle, M. Genes Dev. (1998) [Pubmed]
  4. Receptors for auxin: will it all end in TIRs? Badescu, G.O., Napier, R.M. Trends Plant Sci. (2006) [Pubmed]
  5. Mutations in an Auxin Receptor Homolog AFB5 and in SGT1b Confer Resistance to Synthetic Picolinate Auxins and Not to 2,4-Dichlorophenoxyacetic Acid or Indole-3-Acetic Acid in Arabidopsis. Walsh, T.A., Neal, R., Merlo, A.O., Honma, M., Hicks, G.R., Wolff, K., Matsumura, W., Davies, J.P. Plant Physiol. (2006) [Pubmed]
  6. Arabidopsis SGT1b is required for SCF(TIR1)-mediated auxin response. Gray, W.M., Muskett, P.R., Chuang, H.W., Parker, J.E. Plant Cell (2003) [Pubmed]
  7. The IAA1 protein is encoded by AXR5 and is a substrate of SCF(TIR1). Yang, X., Lee, S., So, J.H., Dharmasiri, S., Dharmasiri, N., Ge, L., Jensen, C., Hangarter, R., Hobbie, L., Estelle, M. Plant J. (2004) [Pubmed]
  8. Plant development is regulated by a family of auxin receptor F box proteins. Dharmasiri, N., Dharmasiri, S., Weijers, D., Lechner, E., Yamada, M., Hobbie, L., Ehrismann, J.S., Jürgens, G., Estelle, M. Dev. Cell (2005) [Pubmed]
  9. The F-box protein TIR1 is an auxin receptor. Dharmasiri, N., Dharmasiri, S., Estelle, M. Nature (2005) [Pubmed]
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