Abscisic Acid Increases Arabidopsis ABI5 Transcription Factor Levels by Promoting KEG E3 Ligase Self-Ubiquitination and Proteasomal Degradation.
The Arabidopsis thaliana RING-type E3 ligase KEEP ON GOING (KEG) is a negative regulator of abscisic acid (ABA) signaling. Seedlings homozygous for T-DNA insertions in KEG accumulate high levels of the ABA-responsive transcription factor ABSCISIC ACID-INSENSITIVE5 (ABI5). Here, we demonstrate that KEG E3 ligase activity is required for the regulation ... of ABI5 abundance. KEG ubiquitinates ABI5 in vitro, and a functional KEG RING domain is required to restore the levels of ABI5 in keg-1 to that of the wild type. Overexpression of KEG leads to ABA insensitivity, which correlates with KEG protein levels. In the presence of ABA, ABI5 levels increase drastically via a decrease in ubiquitin-meditated proteasomal degradation. Our results indicate that ABA promotes ABI5 accumulation by inducing the ubiquitination and proteasomal degradation of KEG. A functional RING domain is required for the ABA-induced degradation of KEG, suggesting that the loss is due to self-ubiquitination. Mutations within KEG's kinase domain or treatments with kinase inhibitors prohibit the ABA-induced ubiquitination and degradation of KEG, indicating that phosphorylation, possibly self-phosphorylation, is involved in the ABA regulation of KEG protein levels. We discuss a model for how ABA may negatively regulate KEG protein abundance, leading to accumulation of ABI5 and ABA-dependent cellular responses.
Mesh Terms:
Amino Acid Sequence, Animals, Basement Membrane, Caenorhabditis elegans, Caenorhabditis elegans Proteins, Cell Movement, Cloning, Molecular, Disintegrins, Extracellular Matrix, Gene Expression Profiling, Genes, Helminth, Glycosylation, Gonads, Metalloendopeptidases, Molecular Sequence Data, Muscles, Mutation, Protein Structure, Tertiary, Recombinant Fusion Proteins, Sequence Alignment, Transgenes
Amino Acid Sequence, Animals, Basement Membrane, Caenorhabditis elegans, Caenorhabditis elegans Proteins, Cell Movement, Cloning, Molecular, Disintegrins, Extracellular Matrix, Gene Expression Profiling, Genes, Helminth, Glycosylation, Gonads, Metalloendopeptidases, Molecular Sequence Data, Muscles, Mutation, Protein Structure, Tertiary, Recombinant Fusion Proteins, Sequence Alignment, Transgenes
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Date: Aug. 03, 2010
PubMed ID: 20682837
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