Characterization of Salicylic Acid-Binding Proteins in Plant Defense Responses

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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. 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. 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.It is now well established that SA plays a key role(s) in the development of resistance in many, but not all, plant-pathogen systems. While our understanding of SA function(s) in disease resistance is far from complete, it is becoming increasingly clear that its role(s) is complex. This increase in the complexity of SA function(s) in defense is matched by the discovery in tobacco of multiple proteins with which SA interacts. An understanding of SA function(s) in defense against microbial pathogens will require the identification and characterization of these proteins, the major objective of this research. This project focuses on SABP2 and SABP3. SABP3 was recently shown to be the tobacco carbonic anhydrase (CA) that is located in the chloroplasts. The first objective is the completion of the cloning of SABP2. The sequence of seven peptides of SABP2 have been obtained and are being used to clone its gene. High priority will be to determine SABP2's role in disease resistance. This will be done by silencing its expression using the PVX-based silencing system and/or by obtaining a knockout mutation in the corresponding gene in Arabidopsis. The second major objective of this project is to determine the nature of SABP3/CA's anti-oxidant activity and whether SA alters this activity. Several approaches will be used. Currently there are available antisense CA transgenic tobacco, which have 98-99% reduction in their carbonic anhydrase enzymatic activity. These plants will be tested for their sensitivity to oxidative stress and resistance to pathogens. In addition, the effects on tobacco SABP3/CA's anti-oxidant activity will be tested. For this a mutant strain of yeast, designated Dnce103, will be employed. Dnce103 is very sensitive to oxidative stress due to a deletion of its CA-like gene. SABP3/CA expressed in this mutant overcomes its sensitivity to oxygen. It is hoped that SA will alter SABP3/CA's effect on this mutant.