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Post-translational regulation of AB13, a key mediator of ABA signaling


Hormones are implicated in almost every aspect of plant growth. Selective proteindegradation by the ubiquitin-proteasome pathway has emerged as a powerful regulatorymechanism in hormone signal transduction. A clear role for ubiquitin-mediated proteolysis o fthe AUX/IAA transcriptional repressers is already demonstrated. Recent studies providedpreliminary evidence for the involvement of ubiquitin-mediated proteolysis in the signalingpathways of other classical plant hormones like cytokinins, gibberellins, eth ylene and ABA.Genetic approaches have generated a number of mutants in ABA biosynthesis or ABAaction. One of the cloned genes encodes ABA-INSENSITIVE3 (ABI3), a positive regulator ofthe late maturation programme in embryogenesis, and simultaneously as a ne gativeregulator of germination programmes. Four ABIS-interacting proteins (AlPs) were identifiedin a yeast 2-hybrid screen. One of these encoded a protein (AIP2) with a C3HC4 RING fingermotif at its C-terminus. As RING-finger proteins are likely to functio n as E3 ligases, anessential component of the ubiquitination machinery, it is reasonable to hypothesize thatAIP2 attenuates ABA signals by down regulating ABI3. In this proposal this hypothesis willbe tested. The interaction between AIP2 and ABI3 will be v erified and other AIP2-interactingproteins will be identified using yeast two-hybrid technology. Their interacting domains willbe identified. To investigate if AIP2 has E3 activity and specifically targets ABI3 as asubstrate, recombinant AIP2 will be used as a source of E3 in an in vitro ubiquitinationexperiment with ABI3 as a substrate. Transgenic plants overexpressing AIP2 will beproduced and analysed together with mutants in AIP2. The expression profiles of AIP2 willbe analysed using transgenic plants ca rrying a fusion protein of the AIP2 promotor and theß-glucuronidase or GFP-gene. Using pull-down experiments, in vitro and in vivo #

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Rijvisschestraat 120

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