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].

References