| The object of this study was to genetically dissect plant disease resistance using Arabidopsis thaliana and the bacterial pathogen Pseudomonas syringae. Genetic and molecular approaches were used to identify components involved in this pathway. A screen was conducted to look for Arabidopsis mutants that failed to display the hypersensitive response (HR) in response to P. syringae expressing avrRpt2. Fourteen mutants were isolated. These mutants were divided into five groups based on their HR phenotype and other morphological changes: the rps2 mutants, HR{dollar}sp-{dollar} mutants, lesion mimic mutants, mixed HR mutants, and fertilization-defective mutants. The HR{dollar}sp-{dollar} mutants failed to produce an HR in response to multiple P. syringae strains carrying different avr genes, but retained their gene-for-gene disease resistance. Because of this phenotype, the mutant loci were named dnd, for "defense, no death". The dnd mutants also exhibited constitutive expression of defense-related genes, elevated levels of endogenous salicylic acid, and enhanced resistance to a wide range of virulent pathogens. Preliminary mapping experiments placed DND1 in a {dollar}sim{dollar}1.6 cM interval between markers CHS1 and nga106 on the top arm of chromosome 5. Results from characterization of the mixed HR mutants N13 and D8 suggested a weaker dnd phenotype in these mutants. |
