Function of the Phytotoxin Coronatine in P. syringae DC3000/Plant Interactions

Washington University, Saint Louis MO

Investigators

Abstract

Coronatine (COR) is a phytotoxin produced by the plant pathogenic bacterium Pseudomonas syringae. COR contributes to the virulence of P. syringae; however, a precise mode of action for COR has not been defined. COR has a unique structure consisting of two distinct compounds: (1) coronafacic acid (CFA), and (2) coronamic acid (CMA). CFA is structurally similar to jasmonic acid (JA), a plant hormone involved in plant defense, and functions as a molecular mimic of this endogenous plant signaling molecule. CMA is a structural analog of aminocyclopropyl carboxylic acid (ACC), the immediate precursor to ethylene, another endogenous plant hormone involved in plant defense. The structural and functional similarities between COR and compounds involved in plant defense signaling (JA and ACC/ethylene) suggest that COR may promote pathogen virulence by interfering with host defense responses and/or with other physiological processes in the plant. Furthermore, we have previously shown that COR is important for early colonization events in host plants, a finding consistent with the suppression or modulation of host defense responses. In the proposed work, a genetic approach that encompasses both host and pathogen will be used to define the role of COR in the pathogenesis of Arabidopsis and tomato. For this purpose, the PI and Co-PI have developed the first well-defined CFA- and CMA- mutants of P. syringae pv. tomato DC3000, a pathogen of Arabidopsis and tomato. The unique expertise and tools in the PI and Co-PI's laboratories will be used to integrate studies of the host (how does COR modulate susceptibility?) with the pathogen (how does COR contribute to virulence?). Specifically, we will: 1) characterize the COR genes in P. syringae pv. tomato strain DC3000 and study the structure and regulation of these genes; 2) investigate the role of COR, CFA and CMA in the pathogenesis of Arabidopsis and tomato by utilizing mutants deficient for production of CFA, CMA, or both molecules; 3) utilize functional genomics (microarray studies) and the DC3000 COR- mutants to investigate the role of COR, CFA, and CMA on modulating host cell processes and defense responses; and 4) analyze the effect of COR, CFA, and CMA on plant cell biology. These studies will contribute to our understanding of the mechanisms involved in disease development in plants. By taking advantage of a system where we can simultaneously study both the pathogen and plant host we will be able to identify and study the mechanisms by which COR alters normal plant cell processes. These studies will provide insight into the molecular basis of COR function in other plant hosts, a contribution that could result in the development of improved strategies for preventing or controlling plant disease in agricultural and horticultural systems.