Polypeptide Signaling in Plants

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Research is proposed to investigate the extent and roles of polypeptide signaling in plants. Animals and yeast utilize polypeptide signals for regulating a host of physiological processes, including stress, reproduction, development and defense, and many others. Until 1991, when this laboratory discovered the first polypeptide signal in plants, the accepted dogma was that plants did not utilize polypeptide signals, but used small chemical hormones such as auxin, cytokinins, gibberillins, ethylene and abscisic acid as regulators of physiological processes. Since the first isolation of a polypeptide signal in 1991, four new polypeptide signals have been identified in other laboratories, and five more have been identified and purified in our laboratory. The signaling polypeptides in plants reported to date are involved in defense, development, and reproduction. Thus, we expect many more to be identified in the near future. We have developed a novel, rapid assay to identify polypeptide signals in plants using suspension-cultured cells, which respond to receptor-mediated polypeptide signals by causing the pH of the cell culture medium to increase. Using the assay to monitor the signaling polypeptides during purification, we have identified five receptor-mediated polypeptide signals from tobacco, tomato and alfalfa and are utilizing the assay to investigate the presence of polypeptides throughout the plant kingdom. We have extensively studied the first discovered polypeptide defense signal that is released upon herbivore and pathogen attacks. It is an 18 amino acid polypeptide isolated from tomato, that is derived from a 200 amino acid precursor. We have published extensively on its signaling pathway in plants and have identified and isolated its receptor on tomato cell membranes. We are currently isolating the receptor gene for studies of the structure and function of the receptor in tomato cells. We are also seeking the genes for the new polypeptides we have isolated to determine their precursors, the mode of release and action, and their localization in plants. We will continue to identify and isolate the receptors of these polypeptides and begin to learn the broad fundamental principles that underlie polypeptide signaling in plants. Our studies of signaling polypeptides and their receptors in plants will provide an entirely new understanding of plant signaling for defense and development, with important relevance to ecology and agriculture.