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Auxin regulates SCFTIR1-dependent degradation of AUX/IAA proteins


The plant hormone auxin is central in many aspects of plant development. Previous studies have implicated the ubiquitin-ligase SCFTIR1 and the AUX/IAA proteins in auxin response. Dominant mutations in several AUX/IAA genes confer pleiotropic auxin-related phenotypes, whereas recessive mutations affecting the function of SCFTIR1 decrease auxin response. Here we show that SCFTIR1 is required for AUX/IAA degradation. We demonstrate that SCFTIR1 interacts with AXR2/IAA7 and AXR3/IAA17, and that domain II of these proteins is necessary and sufficient for this interaction. Further, auxin stimulates binding of SCFTIR1 to the AUX/IAA proteins, and their degradation. Because domain II is conserved in nearly all AUX/IAA proteins in Arabidopsis, we propose that auxin promotes the degradation of this large family of transcriptional regulators, leading to diverse downstream effects.

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Figure 1: Analysis of AUX/IAA–GUS fusion constructs. a, Seven-day-old seedlings stained for GUS activity.
Figure 2: The proteasome inhibitor MG132 increases AUX/IAA protein stability. a, Seven-day-old seedlings were treated with 10 µM MG132 for 2 h and stained for GUS activity.
Figure 3: AUX/IAA proteins exhibit increased stability in axr1 and tir1 mutants.
Figure 4: SCFTIR1 interacts with AUX/IAA proteins. a, Immunoprecipitates (IP) were blotted and probed with the anti-c-myc antibody.
Figure 5: Auxin promotes the SCFTIR1–AUX/IAA interaction.
Figure 6: Model for auxin response.

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This work was supported by grants from the National Institutes of Health (M.E.), the US Department of Energy (M.E.), the Texas Higher Education Coordinating Body Advance Research Program (M.E.) and the UK Biotechnology and Biological Science Research Council (O.L.).

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Correspondence to Mark Estelle.

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Gray, W., Kepinski, S., Rouse, D. et al. Auxin regulates SCFTIR1-dependent degradation of AUX/IAA proteins. Nature 414, 271–276 (2001).

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