Abstract: Hypersensitive response （HR） is an effective way of plants against pathogens. Lesion mimic mutants spontaneously exhibit HR-like cell death in absence of pathogens， and are of great significance in dissecting the molecular mechanisms of disease resistance in plants. In this study， it was found that the resistance against 4 Philippine races and 10 Chinese races was significantly enhanced in the spl5 mutant， indicating that the spl5 mutant displays a broad-spectrum resistance to Xoo. Reactive oxygen species （ROS） were significantly accumulated in spl5 leaves， which is an early feature of HR with reactive oxygen burst， meanwhile, activities of ROS scavenging enzymes such as SOD， POD and CAT significantly changed in spl5， indicating that the imbalance of ROS metabolism might trigger HR occurrence in spl5. In addition， RT-PCR-based assay showed that transcriptional levels of EDS1， AOS2 and LOX2， key regulators in salicylic acid （SA） and jasmonic acid （JA） signaling pathways， respectively， and their downstream pathogenesis-related genes such as PR1a and PR1b were up\|regulated in spl5. Taken together， these results clearly indicated that spl5 mutation might activate both SA and JA signaling pathways and consequently trigger systematic defense responses in plants．

Key words: rice, lesion mimic, spl5, disease-resistant