Molecular Characterization of the Ethylene Receptor ETR1 From Arabidopsis

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The plant hormone ethylene regulates many aspects of growth and development. A family of proteins that act as receptors for ethylene have been identified from Arabidopsis. This research is focused on gaining an understanding of the mechanism by which this family of receptors perceives and transduces the ethylene signal. Expression of the ETR 1 receptor protein in yeast provides a model system in which to study the structure/function relationships of the ethylene binding site. Site directed mutagenesis of the ethylene binding domain of ETR1 and assessment of effects on ethylene binding activity in yeast provides a method for testing and refining a structural model of the ethylene binding domain. Expression in yeast will also continue to provide a source of the ETR1 protein for direct biochemical analysis of receptor function, including continuing analysis of the involvement of copper as a co-factor for binding and investigations into the relationship between ethylene binding and signal output by the transmitter domain of the receptor. Co-expression of different isoforms of the receptor in the same yeast line will allow the investigation of whether heterodimerization of receptor isoforms plays a role in signaling The work in yeast will be complemented by experiments performed in mutant and transgenic plants that will provide a functional context for testing hypotheses concerning receptor function. Dominant effects of introduced mutations in receptor isoforms will be assessed by transferring altered forms of the receptor into wild-type plants and evaluating the effects on the ethylene signaling in vivo using a seedling growth-response assay. Receptor-null mutant backgrounds provide a method for evaluating the effects of recessive mutations in a similar way. Ethylene binding assays in plant tissues in the receptor-null genetic backgrounds will provide information on the contribution each isoform makes to the overall binding activity of plant tissues. These experiments will be supported by the development of isoform-specific antibodies. This research on the first available plant hormone receptor will provide novel information on how ethylene works as a hormone signal and will provide a model for the investigation of other hormone receptors in plants.