Abstract:

【Objective】 The genome bioinformatics of X. oryzae pv. oryzicola (Xoc), which is the causal agent of bacterial leaf streak in rice, reveals that there is a XopQ1Xoc in the pathogen homologous to HopQ1-1 secreted through type-Ⅲ secretion system (T3S) in Pseudomonas syringae pv. tomato DC3000, causing bacterial speck diseases in tomato. However, it is unclear whether XopQ1Xoc is a T3S effector or not and what roles it takes in virulence of Xoc in rice. 【Method】The mutant of Xoc in the xopQ1Xoc gene was generated by knocking-out technique through marker-exchange. 【Result】 Pathogenicity assays demonstrated that the virulence of the mutant in rice was stronger than that caused by Xoc wild-type strain RS105 and the bacterial growth of the mutant in rice tissue was enhanced. Intriguingly, the xopQ1Xoc mutant at 108 CFU/mL still induced hypersensitive response in tobacco, but caused necrosis lesions at 104 CFU/mL after injected into tobacco leaves for 8 days. The complementation assay indicated that the xopQ1Xoc gene restored virulence and bacterial growth in rice and the ability not to cause nescrosis lesions in tobacco to the wild-type RS105. Immunobloting assay confirmed that XopQ1Xoc was not secreted through T3S apparatus if the component HrcV was mutated. 【Conclusion】 These results strongly suggested that XopQ1Xoc is a T3S effector of X. oryzae pv. oryzicola contributing strong virulence to the pathogen in rice by suppressing an unknown target in plant immunity system. This study has provided a basis to understand molecular mechanisms in Xoc-rice interactions.

Key words: Xanthomonas oryzae pv. oryzicola, xopQ1Xoc gene, pathogenicity, T3SS