An Arabidopsis Basic Helix-Loop-Helix Leucine Zipper Protein Modulates Metal Homeostasis and Auxin Conjugate Responsiveness

The plant hormone auxin can be regulated by formation and hydrolysis of amide-linked indole-3-acetic acid (IAA) conjugates. Here, we report the characterization of the dominant Arabidopsis iaa-leucine resistant3 (ilr3-1) mutant, which has reduced sensitivity to IAA-Leu and IAA-Phe, while retaining w...

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Published in:	Genetics (Austin) Vol. 174; no. 4; pp. 1841 - 1857
Main Authors:	Rampey, Rebekah A, Woodward, Andrew W, Hobbs, Brianne N, Tierney, Megan P, Lahner, Brett, Salt, David E, Bartel, Bonnie
Format:	Journal Article
Language:	English
Published:	United States Genetics Soc America 01-12-2006 Genetics Society of America Copyright © 2006 by the Genetics Society of America
Subjects:	Amino Acid Sequence Amino acids Arabidopsis Arabidopsis - genetics Arabidopsis - growth & development Arabidopsis - metabolism Arabidopsis Proteins - genetics Arabidopsis Proteins - metabolism Basic Helix-Loop-Helix Transcription Factors - genetics Basic Helix-Loop-Helix Transcription Factors - metabolism Cloning, Molecular Down-Regulation Gene Expression Regulation, Developmental Gene Expression Regulation, Plant Homeostasis Indoleacetic Acids - pharmacology Investigations Iron - metabolism Leucine Zippers Manganese - metabolism Mass spectrometry Metals Molecular Sequence Data Mutation Oligonucleotide Array Sequence Analysis Plant Growth Regulators - pharmacology Polymerase Chain Reaction Proteins Seedlings - chemistry Sequence Homology, Amino Acid
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Summary:	The plant hormone auxin can be regulated by formation and hydrolysis of amide-linked indole-3-acetic acid (IAA) conjugates. Here, we report the characterization of the dominant Arabidopsis iaa-leucine resistant3 (ilr3-1) mutant, which has reduced sensitivity to IAA-Leu and IAA-Phe, while retaining wild-type responses to free IAA. The gene defective in ilr3-1 encodes a basic helix-loop-helix leucine zipper protein, bHLH105, and the ilr3-1 lesion results in a truncated product. Overexpressing ilr3-1 in wild-type plants recapitulates certain ilr3-1 mutant phenotypes. In contrast, the loss-of-function ilr3-2 allele has increased IAA-Leu sensitivity compared to wild type, indicating that the ilr3-1 allele confers a gain of function. Microarray and quantitative real-time PCR analyses revealed five downregulated genes in ilr3-1, including three encoding putative membrane proteins similar to the yeast iron and manganese transporter Ccc1p. Transcript changes are accompanied by reciprocally misregulated metal accumulation in ilr3-1 and ilr3-2 mutants. Further, ilr3-1 seedlings are less sensitive than wild type to manganese, and auxin conjugate response phenotypes are dependent on exogenous metal concentration in ilr3 mutants. These data suggest a model in which the ILR3/bHLH105 transcription factor regulates expression of metal transporter genes, perhaps indirectly modulating IAA-conjugate hydrolysis by controlling the availability of metals previously shown to influence IAA-amino acid hydrolase protein activity.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 These authors contributed equally to this article. Present address: Baylor College of Medicine, Houston, TX 77030. Corresponding author: Department of Biochemistry and Cell Biology, Rice University, 6100 S. Main St., MS-140, Houston, TX 77005. E-mail: bartel@rice.edu Present address: Center for Computational Biology and Bioinformatics, University of Texas, Austin, TX 78712. Communicating editor: E. J. Richards
ISSN:	0016-6731 1943-2631 1943-2631
DOI:	10.1534/genetics.106.061044