| Plants have evolved a complex network of signaling pathways to defend against the attacks of various microorganisms. To understand how various pathogens trigger different defense responses, how these pathways are regulated and how various pathways interact and cross talk with each other, we have used a genetic approach. Using Arabidopsis thaliana as a model system, various mutants that are compromised in different disease response pathways, have been identified.; In this work I have tried to understand the roles of some of the regulatory genes involved in controlling the defense response pathways. I have described the characterization of two mutants, the enhanced disease susceptibility mutant eds4 and the phytoalexin deficient mutant pad2, which show defects in the salicylic mediated defense responses, after infection by the bacterial pathogen Psm ES4326. Further, I have described the cloning of the PAD2 gene, which has been found to be a novel gene of unknown functions. My studies on these two mutants explain the roles of these genes in plant defense responses. There is also an emerging hypothesis about the cross-talk and interactions among different signaling pathways that are controlled by different plant hormones like salicylic acid, jasmonic acid and ethylene. This work also describes evidence of synergy and antagonism between the salicylic acid and the jasmonic acid/ethylene mediated defense responses. |
