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The F-box protein TIR1 is an auxin receptor

Naturevolume 435pages441445 (2005) | Download Citation



The plant hormone auxin regulates diverse aspects of plant growth and development. Recent studies indicate that auxin acts by promoting the degradation of the Aux/IAA transcriptional repressors through the action of the ubiquitin protein ligase SCFTIR1. The nature of the signalling cascade that leads to this effect is not known. However, recent studies indicate that the auxin receptor and other signalling components involved in this response are soluble factors. Using an in vitro pull-down assay, we demonstrate that the interaction between transport inhibitor response 1 (TIR1) and Aux/IAA proteins does not require stable modification of either protein. Instead auxin promotes the Aux/IAA–SCFTIR1 interaction by binding directly to SCFTIR1. We further show that the loss of TIR1 and three related F-box proteins eliminates saturable auxin binding in plant extracts. Finally, TIR1 synthesized in insect cells binds Aux/IAA proteins in an auxin-dependent manner. Together, these results indicate that TIR1 is an auxin receptor that mediates Aux/IAA degradation and auxin-regulated transcription.

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We thank R. Dumas for technical assistance and C. Leblanc for help with insect cell culture. In addition, we thank S. Kepinski and O. Leyser for discussions. Research in the authors' laboratory is supported by grants from the NIH, the NSF and the DOE.

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  1. Department of Biology, Indiana University, Bloomington, Indiana, 47405, USA

    • Nihal Dharmasiri
    • , Sunethra Dharmasiri
    •  & Mark Estelle


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Reprints and permissions information is available at The authors declare no competing financial interests.

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Correspondence to Mark Estelle.

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