Characterization of the High Affinity Salicylic Acid-Binding Protein 2 in Plant Disease Resistance

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Intellectual Merit: Broad-spectrum resistance to a wide array of pathogens, know as systemic acquired resistance (SAR), can be activated by infection with a pathogen or treatment with SAR-inducing natural chemicals such as salicylic acid (SA) and its synthetic functional analogues, INA or BTH. Salicylic acid (SA) is an important endogenous signal required for the activation of various local and systemic defense responses associated with plant innate immunity. To investigate how the SA signal is transduced, a tobacco SA-binding protein (SABP)2 that binds SA with high affinity has been identified. SABP2 shows strong esterase activity for methyl SA (MeSA), its preferred substrate. SA is a potent inhibitor of this catalysis. These observations are consistent with crystal structure analyses showing that MeSA readily fits into SABP2's active site and that SA also binds this site. Since silencing of SABP2 suppresses disease resistance, particularly SAR, SABP2 likely functions to convert biologically inactive MeSA into active SA as part of the signal transduction pathways that activate SAR and perhaps also local defense responses. The long-term objectives of this proposal are to decipher SABP2's role(s) in disease resistance and its mechanism(s) of action, thereby testing the above hypothesis. To achieve these objectives, the effect of altered SABP2 expression on disease resistance is being determined and whether or not MeSA is SABP2's natural substrate is being assessed. Using a novel complementation approach together with mutational analysis the importance of SABP2's esterase and SA-binding activities will be addressed. In addition, whether SABP2 is involved in producing/transmitting the mobile SAR signal or responding to this signal will be assessed.Broader Impacts: Plant disease causes an estimated loss worldwide of $100B annually. A variety of strategies are being developed to protect plants against disease. One approach is to induce the plant's own natural defenses. This strategy is attractive since it can provide protection against a broad spectrum of pathogens. The development of strategies that control disease by manipulating endogenous plant defense responses will be very important for sustaining agricultural production and improving our environment and health. The proposed research will provide a stimulating training environment for graduate and postdoctoral students, where they are exposed to a large repertoire of biochemical, molecular, genetic, pharmacological, and physiological approaches to address a complex biological question. In addition, this project will continue to provide undergraduates with opportunities to experience first-hand the excitement of discovery under the close mentorship of a postdoctoral fellow, research associate or graduate student during the academic year or in the BTI/Cornell Summer Internship Program. It also enables these graduate and postgraduate students to develop their teaching and mentoring skills.