Abstract
The expression of auxin-responsive genes is regulated by the TIR1/AFB auxin receptor-dependent degradation of Aux/IAA transcriptional repressors, which interact with auxin-responsive factors (ARFs). Most of the 29 Aux/IAA genes present in Arabidopsis have not been functionally characterized to date. IAA8 appears to have a distinct function from the other Aux/IAA genes, due to its unique transcriptional response to auxin and the stability of its encoded protein. In this study, we characterized the function of Arabidopsis IAA8 in various developmental processes governed by auxin and in the transcriptional regulation of the auxin response. Transgenic plants expressing estrogen-inducible IAA8 (XVE::IAA8) exhibited significantly fewer lateral roots than the wild type, and an IAA8 loss-of-function mutant exhibited significantly more. Ectopic overexpression of IAA8 resulted in abnormal gravitropism. The strong induction of early auxin-responsive marker genes by auxin treatment was delayed by IAA8 overexpression. GFP-fusion analysis revealed that IAA8 localized not only to the nucleus, but, in contrast to other Aux/IAAs, also to the cytosol. Furthermore, we demonstrated that IAA8 interacts with TIR1, in an auxin-dependent fashion, and with ARF proteins, both in yeast and in planta. Taken together, our results show that IAA8 is involved in lateral root formation, and that this process is regulated through the interaction with the TIR1 auxin receptor and ARF transcription factors in the nucleus.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Arabidopsis / genetics*
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Arabidopsis / growth & development
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Arabidopsis / metabolism
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Arabidopsis Proteins / genetics*
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Arabidopsis Proteins / metabolism
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Cell Nucleus / metabolism
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Cytosol / metabolism
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DNA-Binding Proteins / genetics*
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DNA-Binding Proteins / metabolism
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F-Box Proteins / genetics*
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F-Box Proteins / metabolism
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Gene Expression Regulation, Developmental / drug effects
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Gene Expression Regulation, Plant / drug effects
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Indoleacetic Acids / pharmacology
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Luminescent Proteins / genetics
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Luminescent Proteins / metabolism
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Microscopy, Confocal
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Mutation
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Plant Growth Regulators / pharmacology
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Plant Roots / genetics*
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Plant Roots / growth & development
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Plant Roots / metabolism
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Plants, Genetically Modified
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Protein Binding / drug effects
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Protoplasts / cytology
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Protoplasts / metabolism
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Receptors, Cell Surface / genetics*
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Receptors, Cell Surface / metabolism
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Reverse Transcriptase Polymerase Chain Reaction
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Transcription Factors / genetics*
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Transcription Factors / metabolism
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Two-Hybrid System Techniques
Substances
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ARF1 protein, Arabidopsis
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Arabidopsis Proteins
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DNA-Binding Proteins
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F-Box Proteins
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IAA8 protein, Arabidopsis
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Indoleacetic Acids
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Luminescent Proteins
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Plant Growth Regulators
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Receptors, Cell Surface
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TIR1 protein, Arabidopsis
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Transcription Factors
Grants and funding
This work was carried out partially under the NIBB Cooperative Research Program (7–342, 8–101, 9–102), and supported in part by a Grant-in-Aid for Scientific Research of Priority Areas on ‘Organelle Differentiation as the Strategy for Environmental Adaptation in Plants’ (no. 1685101) and a Grant-in-Aid for Young Scientists (B) (no. 23770045) from the Japanese Ministry of Education, Sports, Culture, Science and Technology, Saneyoshi Scholarship Foundation, Sumitomo Foundation, and Inamori Foundation to H.K. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.