The conserved Xanthomonas effector XopM targets allene oxide synthase OsAOS3 and interferes with jasmonate-mediated defense in rice1

Bacterial blight (BB) of rice caused by the phytopathogenic bacterium Xanthomonas oryzae pv. oryzae ( Xoo ) is a disease of global importance. Xoo utilizes the type III secretion system (T3SS) and its effectors for virulence, and XopM is a conserved T3SS effector in Xanthomonas spp. However, the virulence function of XopM is largely unknown. In this study, we show that XopM contributes to Xoo virulence in rice. We demonstrate that XopM interacts with allene oxide synthase OsAOS3, a key enzyme involved in jasmonic acid (JA) biosynthesis. The expression levels of OsAOS3 and three homologues of OsAOS were elevated after Xoo infection. Knockout mutants of OsAOS3 exhibited decreased JA accumulation and reduced resistance to Xoo and X. oryzae pv. oryzicola . Moreover, JA-related defense genes were downregulated in osaos3 mutants during Xoo infection. Based on our results, we propose a model showing how XopM hijacks OsAOS3 to interfere with JA-mediated defenses, leading to a suppression of rice immunity. Our findings reveal a novel virulence strategy where Xanthomonas pathogens interfere with the JA pathway and modulate the host defense response.