Research is proposed to investigate the intracellular signal transduction pathways that regulate the synthesis of defensive proteinase inhibitor proteins in plant leaves in response to herbivore and pathogen attacks. Our previous research has provided strong evidence that the inducible signalling pathways that regulate two proteinase inhibitor genes in tomato, potato, and alfalfa plants, and likely in other plants as well, involve a lipid-based system that results in the production of jasmonic acid as a key signalling molecule. The evidence suggests that insect or pathogen attacks produce extracellular signals that interact with the plant cell membrane to release linolenic acid. Linolenic acid is known to be converted to jasmonic acid through several biochemical steps. Both linolenic acid and jasmonic acid are powerful inducers of the inhibitor genes when placed on leaf surfaces, indicating their involvement in the signalling pathway. The research funded by this grant will seek the mechanism within the plant membranes that releases linolenic acid in response to signals produced by insect or pathogen attacks and will establish the biochemical events leading to the synthesis of jasmonic acid. The mechanism by which jasmonic acid can activate proteinase inhibitor gene expression in the plant cell nucleus will also be studied. The fate of jasmonic acid and its receptor will be sought, and its role in gene activation will be investigated. The information will be utilized to understand the biochemical basis of inducible plant defenses against insects and pathogens.
