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Nat Chem Biol. 2012 Apr 1;8(5):477-85. doi: 10.1038/nchembio.926.

A combinatorial TIR1/AFB-Aux/IAA co-receptor system for differential sensing of auxin.

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1
Section of Cell and Developmental Biology, University of California-San Diego, La Jolla, California, USA.

Abstract

The plant hormone auxin regulates virtually every aspect of plant growth and development. Auxin acts by binding the F-box protein transport inhibitor response 1 (TIR1) and promotes the degradation of the AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) transcriptional repressors. Here we show that efficient auxin binding requires assembly of an auxin co-receptor complex consisting of TIR1 and an Aux/IAA protein. Heterologous experiments in yeast and quantitative IAA binding assays using purified proteins showed that different combinations of TIR1 and Aux/IAA proteins form co-receptor complexes with a wide range of auxin-binding affinities. Auxin affinity seems to be largely determined by the Aux/IAA. As there are 6 TIR1/AUXIN SIGNALING F-BOX proteins (AFBs) and 29 Aux/IAA proteins in Arabidopsis thaliana, combinatorial interactions may result in many co-receptors with distinct auxin-sensing properties. We also demonstrate that the AFB5-Aux/IAA co-receptor selectively binds the auxinic herbicide picloram. This co-receptor system broadens the effective concentration range of the hormone and may contribute to the complexity of auxin response.

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PMID:
22466420
PMCID:
PMC3331960
DOI:
10.1038/nchembio.926
[Indexed for MEDLINE]
Free PMC Article

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