Identical Amino Acid Substitutions in the Repression Domain of Auxin/Indole-3-Acetic Acid Proteins Have Contrasting Effects on Auxin Signaling

• Published in: Plant physiology (Bethesda) Vol. 155; no. 3; pp. 1252 - 1263
• Main Authors: Li, Hanbing, Tiwari, Shiv B, Hagen, Gretchen, Guilfoyle, Tom J
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.03.2011
• Subjects: Amino Acid Substitution - genetics; Arabidopsis - genetics; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Auxins; Biological and medical sciences; DEVELOPMENT AND HORMONE ACTION; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Genetic mutation; Indoleacetic Acids - metabolism; Insulin antibodies; Models, Biological; Mutation - genetics; Phenotype; Phenotypes; Plant physiology and development; Plants; Plants, Genetically Modified; Promoter Regions, Genetic - genetics; Protein Structure, Tertiary; Proteins; Reporter genes; Repression; Repressor Proteins - chemistry; Repressor Proteins - genetics; Repressor Proteins - metabolism; Seedlings; Signal Transduction; Transformation, Genetic; Transgenes; Transgenes - genetics; Auxin; Substitution; Plant physiology; Indoleacetic acid; Aminoacid; Plant growth substance; Repression; Protein
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.110.171322

Auxin/indole-3-acetic acid (Aux/IAA) proteins function as repressors of auxin response gene expression when auxin concentrations in a cell are low. At elevated auxin concentrations, these repressors are destroyed via the ubiquitin-proteasome pathway, resulting in derepression/activation of auxin response genes. Most Aux/IAA repressors contain four conserved domains, with one of these being an active, portable repression domain (domain I) and a second being an auxin-dependent instability domain (domain II). Here, we have analyzed the effects of amino acid substitutions in the repression domain of selected Aux/IAA proteins. We show that stabilized versions of Aux/IAA proteins with amino acid substitutions in domain I display contrasting phenotypes when expressed in transformed Arabidopsis (Arabidopsis thaliana) plants. An alanine-for-leucine substitution in the LxLxL (where L is leucine and x is another amino acid) repression domain of IAA3, IAA6, or IAA19 confers enhanced auxin response gene expression and "high-auxin" phenotypes when expressed from the 35S or IAA19 promoter (as tested with IAA19) in transformed Arabidopsis plants. In marked contrast, a single alanine-for-leucine substitution in domain I of IAA12 or IAA17 confers repression of auxin response genes and "low-auxin" phenotypes. These results point to intrinsic differences in the repression domain(s) of IAA proteins and suggest that some IAA proteins have stronger or more complex repression domains than others.