Genetic dissection of N mediated signal transduction in tomato

(Amy deHart, University of California, Berkeley)
We are interested in isolating components on the N-mediated signal transduction pathway. Our approach is to isolate and characterize N gene suppressor mutants. We anticipate that this work will lead to a better understanding of the molecular mechanisms of plant disease resistance.The N gene confers a temperature sensitive hypersensitive response to tobacco mosaic virus (TMV) and effectively restricts TMV to sites of inoculation in transgenic tomato, as it does in tobacco (Whitham et al, 1996). The ability to reconstruct the N-mediated resistance response to TMV in tomato demonstrates that all the components necessary for N-mediated resistance are conserved in tomato, making it an ideal genetic system to isolate and study components of the N signal transduction pathway.Based on the temperature-sensitive nature of N, we have developed an efficient seedling lethal screen for isolation of N-suppressor mutants. The transgenic tomato::NN line has been mutagenized with fast-neutrons, and the seedling lethal screen has been successfully employed to isolate putative N-suppressors. One fast-neutron mutant, son1, has been identified and characterized. Cloning of the gene corresponding to son1 should lead to a better understanding of the mechanism N-mediated TMV resistance.