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- Title
Abscisic Acid Increases Arabidopsis ABI5 Transcription Factor Levels by Promoting KEG E3 Ligase Self-Ubiquitination and Proteasomal Degradation.
- Authors
Liu, Hongxia; Stone, Sophia L.
- Abstract
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.
- Subjects
TRANSCRIPTION factors; UBIQUITIN ligases; ABSCISIC acid; KINASE inhibitors; UBIQUITINATION
- Publication
Plant Cell, 2010, Vol 22, Issue 8, p2630
- ISSN
1040-4651
- Publication type
Article
- DOI
10.1105/tpc.110.076075