ELUCIDATION OF THE MOLECULAR-GENETIC AND BIOCHEMICAL BASIS OF N-MEDIATED TMV RESISTANCE B.J. BAKER1,2, C. CORRl, M. DUITONl, H.- H.CHANGl, F. L. ERICKSO&l, SP HOLZBERG3, SP DINESH-KUMAR, A. A. CALDERON- URREA5, C. USTACH1, S. WHITHAM4 1) Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA; 2) Plant Gene Expression Center, University of Cahfomia and United States Department of Agriculture-Agriculture Research Service, Albany, CA 947 10, USA; 3) Dept. of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94710 USA, 4) Institute of Biological Chemistry, Washington State University, Pullman, WA, 99164-6340, 5) USA, Dept. of Biology, California State University, Fresno, CA 93740 USA. Our goal is to elucidate the mechanism of R gene-mediated plant resistance to athogen e (R) genes, diseases. The cloning and characterization of several plant disease resistanc P including the N gene from our lab is leading to the elucidation of the molecular basis of disease resistance to a wide range of phytopathogens. Our research is directed at determination of how R gene products specifically recognize pathogen elicitors, how signals are transduced leading to resistance and defense responses, identification of defense response genes and elucidation of how the plant defense responses block pathogen growth and protect the plant from other invading pathogens. We are also interested in isolating new R genes for molecular mechanism studies and for crop protection. The results of our basic research on the mechanism of disease resistance gene action will allow the manipulation of defense pathways for expression of broad spectrum disease resistance to phytopathogens. We hypothesize that N encodes a cytoplasmic receptor or a critical component of a protein complex that specifically recognizes a TMV protein and triggers signal transduction leading to induction of the hypersensitive response (HR), restriction of virus spread and systemic acquired resistance (SAR). To unravel the mechanisms of N-mediated resistance we are investigating (1) regulatio n of N gene expression (2) the structure-function relationship of the s, (3) the structure, biochemical properties and cellular localization of cation and characterization of the TMV protein required for tance (5) identification of components of the resistance signal transduction pathway by genetic dissection of the N resistance pathway and by (6) identification of cellular, N-interacting proteins, and (7) identification of genes with structural and/or functional similarities for comparative studies and for isolation of new genes for crop protection applications. References 1 - Whitham S, Dinesh-Kumar SP, Choi D, Hehl R, Corr C, Baker B, 1994. Cell 78, 1101 --1115. 2. Whitham S., McCormick S, Baker B, 1996. Proc. Natl. Acad. Sci. USA 98, 8776-8781. 3. Baker B, Zambryski P, Staskawicz B, Dinesh-Kumar SP, 1997. Science 276, 726-733.