Mutations in the TIR1 Auxin Receptor That Increase Affinity for Auxin/Indole-3-Acetic Acid Proteins Result in Auxin Hypersensitivity

Hong Yu,Jennifer L Nemhauser,Michael Prigge,Britney L Moss,Seunghee S Jang,Eric Klavins,Mark Estelle

doi:10.1104/pp.113.215582

Hong Yu, Jennifer L Nemhauser + Show 5 more

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https://doi.org/10.1104/pp.113.215582

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Abstract

The phytohormone auxin regulates virtually every aspect of plant development. The hormone directly mediates the interaction between the two members of the auxin coreceptor complex, a TRANSPORT INHIBITOR RESPONSE (TIR1)/AUXIN SIGNALING F-BOX protein and an AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) transcriptional repressor. To learn more about the interaction between these proteins, a mutant screen was performed using the yeast (Saccharomyces cerevisiae) two-hybrid system in Arabidopsis (Arabidopsis thaliana). Two tir1 mutations were identified that increased interaction with Aux/IAAs. The D170E and M473L mutations increase affinity between TIR1 and the degron motif of Aux/IAAs and enhance the activity of the SCF(TIR1) complex. This resulted in faster degradation of Aux/IAAs and increased transcription of auxin-responsive genes in the plant. Plants carrying the pTIR1:tir1 D170E/M473L-Myc transgene exhibit diverse developmental defects during plant growth and display an auxin-hypersensitive phenotype. This work demonstrates that changes in the leucine-rich repeat domain of the TIR1 auxin coreceptor can alter the properties of SCF(TIR1).

Highlights

The plant hormone indole-3-acetic acid (IAA) is the most important natural auxin, with the ability to regulate virtually every aspect of plant development (Woodward and Bartel, 2005; Möller and Weijers, 2009; Sundberg and Østergaard, 2009; Takahashi et al, 2009; Overvoorde et al, 2010; Vernoux et al, 2010)
Previous studies showed that the LexA yeast two-hybrid system can be used to study the interaction between auxin receptors TIR1/AFB and their substrates the AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) (Prigge et al, 2010; Calderón Villalobos et al, 2012)
The TIR1/AFB proteins interact with the Aux/IAAs in an auxin concentration-dependent manner

Summary

Introduction

The plant hormone indole-3-acetic acid (IAA) is the most important natural auxin, with the ability to regulate virtually every aspect of plant development (Woodward and Bartel, 2005; Möller and Weijers, 2009; Sundberg and Østergaard, 2009; Takahashi et al, 2009; Overvoorde et al, 2010; Vernoux et al, 2010). The transcriptional activity of the ARF proteins is inhibited through an interaction with an Aux/IAA protein and the corepressor TOPLESS (Reed, 2001; Tiwari et al, 2001; Weijers et al, 2005; Guilfoyle and Hagen, 2007; Szemenyei et al, 2008). The core region of domain II is a six-amino acid sequence (VGWPPV/I) called the degron, which is required for proteolytic degradation of the Aux/IAA proteins (Worley et al, 2000; Ramos et al, 2001; Dreher et al, 2006). The TIR1 structure in complex with auxin, ASK1 (for Arabidopsis SKP1-LIKE1), and the degron motif from IAA7 revealed that the 18 Leu-rich repeat (LRR) domain forms an auxin-binding pocket and binding surface for the Aux/IAA protein (Tan et al, 2007).

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