Abstract
We screened for mutants of Arabidopsis thaliana that displayed enhanced disease resistance to the powdery mildew pathogen Erysiphe cichoracearum and identified the edr3 mutant, which formed large gray lesions upon infection with E. cichoracearum and supported very little sporulation. The edr3-mediated disease resistance and cell death phenotypes were dependent on salicylic acid signaling, but independent of ethylene and jasmonic acid signaling. In addition, edr3 plants displayed enhanced susceptibility to the necrotrophic fungal pathogen Botrytis cinerea, but showed normal responses to virulent and avirulent strains of Pseudomonas syringae pv. tomato. The EDR3 gene was isolated by positional cloning and found to encode Arabidopsis dynamin-related protein 1E (DRP1E). The edr3 mutation caused an amino acid substitution in the GTPase domain of DRP1E (proline 77 to leucine) that is predicted to block GTP hydrolysis, but not GTP binding. A T-DNA insertion allele in DRP1E did not cause powdery mildew-induced lesions, suggesting that this phenotype is caused by DRP1E being locked in the GTP-bound state, rather than by a loss of DRP1E activity. Analysis of DRP1E-green fluorescent protein fusion proteins revealed that DRP1E is at least partially localized to mitochondria. These observations suggest a mechanistic link between salicylic acid signaling, mitochondria and programmed cell death in plants.