Klessig 9723952 Characterization of the Salicylic Acid Signal Transduction Pathway in Plant Defense Responses An ever increasing body of evidence indicates that salicylic acid (SA) is an important endogenous signal required for activation and/or potentiation of defense responses in both local and systemic resistance. This research will continue studies to identify, clone, and characterize the components of the SA signal transduction pathway(s) which lead to activation of defense responses, in particular pathogenesis-related (PR) gene expression. Two major objectives will continue to be pursued: i) characterization of Arabidopsis mutants with altered SA signal transduction and ii) characterization of PR-2d promoter binding proteins potentially involved in SA responsiveness. A combination of genetic, molecular, and biochemical approaches are being utilized in Arabidopsis and Nicotiana tabacum (tobacco). Genetic approaches include isolation and characterization of Arabidopsis mutants and construction of transgenic Arabidopsis and tobacco plants to identify and characterize cis- and trans-acting components of the SA/defense signaling pathway(s). Molecular approaches include cloning, DNA sequencing, Southern, northern, and western blotting, yeast one- and two-hybrid screening, site-directed mutagenesis, and production of recombinant proteins. Protein purification, enzyme analysis, and characterization of protein-DNA or protein-protein interactions represent some of' the biochemical tools that are being used to further characterize potential pathway components. Both viral (tobacco mosaic virus TMV and turnip crinkle virus TCV ) and bacterial (Pseudomonas syringae pv tomato, maculicola, or tabaci) pathogens are being used to activate the defense pathway(s) and study its components. A key difference between resistant and susceptible plants is the timely recognition of the invading pathogen and the rapid and effective activation of host defenses. Thus, one of the major aims of stu dying plant disease resistance is to identify and characterize plant components which are crucial for the signal transduction processes leading to activation of these host defenses. Identification and characterization of these components are essential to our understanding of the mechanisms of disease resistance. Furthermore, their manipulation through genetic and molecular approaches offers the exciting prospect of enhancing plant disease resistance.
