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

• Published in: Nature chemical biology Vol. 8; no. 5; pp. 477 - 485
• Main Authors: Calderón Villalobos, Luz Irina A, Lee, Sarah, De Oliveira, Cesar, Ivetac, Anthony, Brandt, Wolfgang, Armitage, Lynne, Sheard, Laura B, Tan, Xu, Parry, Geraint, Mao, Haibin, Zheng, Ning, Napier, Richard, Kepinski, Stefan, Estelle, Mark
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01-04-2012; Nature Publishing Group
• Subjects: 631/449/1741/1576; 631/449/2653; 631/80/86/2363; Acetic acid; Amino Acid Sequence; Arabidopsis Proteins - chemistry; Binding sites; Biochemical Engineering; Biochemistry; Bioorganic Chemistry; Cell Biology; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; DNA-Binding Proteins - chemistry; F-Box Proteins - chemistry; Herbicides; Herbicides - chemistry; Hormones; Indoleacetic Acids - chemistry; Molecular Sequence Data; Nuclear Proteins - chemistry; Picloram; Picloram - chemistry; Plant biology; Plant growth; Proteins; Receptors, Cell Surface - chemistry; Signal transduction; Yeasts
• ISSN: 1552-4450; 1552-4469
• DOI: 10.1038/nchembio.926

Auxin is perceived by a co-receptor complex that contains a TIR1 F-box protein and an Aux/IAA transcriptional repressor. The combinatorial diversity of auxin co-receptor complexes and their distinct spectra of affinities offer a means to tune plant cell sensitivity to a wide range of auxin concentrations.
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.