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Abstract Detail


ABA and Ethylene

Stone, Sophia [1], Williams, Luis [2], Farmer, Lisa [3], Vierstra, Richard [3], Callis, Judy [2].

KEG, a Novel RING E3/Kinase/Ankyrin Protein Essential for Arabidopsis Growth and Development is Involved in Abscisic Acid Signaling.

Ubiquitin-dependent protein degradation regulates numerous eukaryotic cellular processes by selectively targeting proteins for degradation by the 26S proteasome. Recent studies have highlighted the role of ubiquitination, specifically E3 ligases, in plant growth and development, hormone signaling and photomorphogenesis. The Arabidopsis proteome contains 469 RING-type E3 ligases, which are further classified into 30 different sub-groups based on domain organization. Of particular interest is the KEG protein, which belongs to the RING-ankyrin sub-group. In addition to the RING-HCa domain and nine ankyrin repeats, KEG also contains a serine/threonine kinase domain as well as a twelve previously unidentified HERC2-like repeats. Both the RING and kinase domains were functional in in vitro ubiquitination and phosphorylation assays, respectively. To determine the function of KEG we analyzed four independent T-DNA insertional lines. keg seedlings exhibit characteristics of post-germinative growth arrest, such as inhibited cotyledon greening and expansion, indicative of elevated abscisic acid (ABA) signaling, a major phytohormone that plays a key role in plant development and survival under unfavorable conditions. As expected, keg seedlings are hypersensitive to exogenous sugars and keg roots are extremely sensitive to the inhibitory effects of ABA on root growth. The observations that KEG accumulates high levels of ABSCISIC ACID-INSENSITIVE5 (ABI5) without exogenous ABA, interacts with ABI5 in vitro, and that loss of ABI5 rescues the growth-arrest phenotype of keg seedlings point to a central role for KEG in regulating ABI5 protein levels and ABA signaling.


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1 - Dalhousie University, Department of Biology, 1355 Oxford Street, 5134 Life Science Center, Halifax, NS, B3H 4J1, Canada
2 - University of California-Davis, Section of Molecular and Cellular Biology
3 - University of Wisconsin-Madison, Deparment of Genetics

Keywords:
RING E3 ligase
ubiquitination
Abscisic Acid
kinase
ABI5
Hormone signaling
Phosphorylation
Post-germination development
protein degradation
Ankyrin repeats
Stress response.

Presentation Type: ASPB Minisymposium
Session: M24
Location: Continental B/Hilton
Date: Wednesday, July 11th, 2007
Time: 8:55 AM
Number: M24002
Abstract ID:711


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