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PUBLISHED ONLINE: 1 APRIL 2012 | http://www.nature.com/doifinder/10.1038/nchembio.926
Web End =DOI: 10.1038/NCHEMBIO.926
A combinatorial TIR1/AFBAux/IAA co-receptor system for differential sensing of auxin
Luz Irina A Caldern Villalobos1,2,10, Sarah Lee3, Cesar De Oliveira4, Anthony Ivetac4,
Wolfgang Brandt5, Lynne Armitage6, Laura B Sheard7,8,11, Xu Tan7,8,10, Geraint Parry1,2,9, Haibin Mao7,8, Ning Zheng7,8, Richard Napier3, Stefan Kepinski6 & Mark Estelle1,2*
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 AFB5Aux/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.
npg 2012 Nature America, Inc. All rights reserved.
IAA (http://www.nature.com/nchembio/journal/v8/n5/compound/nchembio.926_comp1.html
Web End =1 ) is a small tryptophan-derived phytohormone that regulates many plant growth and developmental processes1 including embryogenesis2,3, tropic growth4, leaf formation5, stem elongation6,
root elongation7 and fruit development8. A number of synthetic auxinic compounds have also been identified, most notably 1-naphthaleneacetic acid (1-NAA, http://www.nature.com/nchembio/journal/v8/n5/compound/nchembio.926_comp2.html
Web End =2 ) and the widely used herbicides 2,4-dichlorophenoxyacetic acid (2,4-D, http://www.nature.com/nchembio/journal/v8/n5/compound/nchembio.926_comp3.html
Web End =3 ) and picolinate derivatives instanced by 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid (picloram, http://www.nature.com/nchembio/journal/v8/n5/compound/nchembio.926_comp4.html
Web End =4 )9. Recent studies have produced a coherent model for auxin perception and transcriptional regulation. At low auxin levels, Aux/IAA transcriptional repressors1012, together with co-repressor proteins including TOPLESS13,14, repress genes targeted by auxin response factor (ARF)15,16 transcriptional activators16,17. When auxin levels rise, the Aux/IAA proteins are degraded by the 26S protea-some18, resulting in derepression of ARFs and activation of transcriptional responses19. In Arabidopsis, 29 Aux/IAA proteins have been identified, most of which share a similar domain structure....