MCB-9603679 Schaller Technical The simple gas ethylene functions as an endogenous growth regulator in plants, and affects seed germination, seedling growth, abscission, senescence, fruit ripening, and pathogen responses. The initial steps by which plants perceive and transduce the ethylene signal have begun to be elucidated by studies in the plant Arabidopsis thaliana. From this work it has been demonstrated that a family of ethylene receptors exist in plants that are related to bacterial histidine kinases. Additional evidence indicates that downstream of the ethylene receptors lies a MAP kinase pathway. Thus, signal transduction elements characteristic of both prokaryotic and eukaryotic systems have been combined in a single pathway. The proposed research is designed to determine how the ethylene signal is transduced through the receptor and passed to downstream elements in the signaling pathway. Ethylene receptors will be characterized in reference to their bacterial counterparts. The membrane location of the ethylene receptors in plants will be determined by biochemical fractionation methods. The postulated kinase activity of the receptors will be examined following transgenic expression and purification of the protein from bacteria and yeast. Purification of full-length ethylene receptors from transgenic yeast will allow analysis as to how binding of ethylene regulates kinase activity. In addition, the mechanism of action of the ethylene receptors will be examined in detail by transforming mutant versions back into Arabidopsis and determining how ethylene signal transduction is affected. Ethylene receptors are hypothesized to function through a response regulator protein that feeds into the MAP kinase pathway, and potential response regulators have been identified in Arabidopsis. Their role in ethylene signal transduction will be characterized by knock-out mutations and the ability to interact with known elements in the pathway. This wo rk will clarify the early steps in ethylene signal transduction and provide a framework for engineering modifications into these steps. Modifications of ethylene sensitivity will enhance our ability to regulate such processes as abscission and fruit-ripening in crops of agronomic importance. In a broader context, these studies will also help elucidate how the bacterial histidine kinases have been adapted to function in a eukaryotic system. Nontechnical The gas ethylene is a plant hormone that both signals and induces a variety of responses including ripening and senescence. The efflux of ethylene from some cells stimulates the response of adjacent cells and plants. Ethylene is widely used to induce ripening of some fruit such as tomato and the interruption of ethylene production has been shown to extend the shelf life of transgenic tomatoes that are now commercially available. This project will investigate the fundamental mechanism of how ethylene is perceived by targeted cells. Ethylene is detected by a protein on the surface of plant cells and signals the cell to undertake the stimulation of a number of genes that mediate the ripening and senesence response. This project will elucidate the mechanism of signaling that occurs as a consequence of ethylene detection. The elucidation of the signaling mechanism for ethylene will be an important advance in the understanding of the fundamental biology of plants and it will present the prospect of producing new and useful changes in food and floral crops to permit controlled ripening and longer-lived produce and flowers.
