Polypeptide Signaling in Plants: Structure, Function, Evolution and Mechanism of Action of Systemin and Its Precursor, Prosystemin

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9601099 Ryan The objective of this research is to understand the fundamental processes involved in the synthesis and storage of the 200 amino acid prohormone protein, prosystemin, and the mechanisms of processing, release and mode of reception of the 18 amino acid polypeptide hormone, systemin, that is derived from prosystemin in response to wounding by herbivore attacks. The specific cell types in which prosystemin is synthesized will be identified and the sites of its inter- or intracellular storage will be established. The mechanism by which wounding causes processing and release of systemin from prosystemin will be studied, and research to identify the specific novel processing enzymes will be carried out. The processing enzymes will be purified and characterized. The mode of transport of systemin in tomato plants will be investigated and the mechanism(s) of its reception in target cells will be studied at the biochemical and subcellular levels. The full spectrum of proteins that are activated by systemin will be identified, purified and cloned. Prosystemin protein, produced in an E. coli expression system, will be produced in mg quantities to determine its three dimensional structure, and to relate the stuctural features to its storage and processing. The occurrence of prosystemin homologs throughout the plant kingdom will be systematically sought using prosystemin antibodies, cDNA hybridization analyses, and PCR analyses. The role of prosystemin and systemin in systemically activating defense genes in plant species other than tomato will be studied. The possiblity that polypeptide hormones other than systemin may be derived from the prosystemin protein will be examined. Systemin is the only peptide hormone identified in plants to date. It has a role in plant defense against insects and other insults. This research will contribute to our fundamental understanding of how plants cope with stresses that they encounter during their life cycle.