【Objective】 Xanthomonas outer proteins (Xops) are conservatively virulent effectors or virulence-assistant components secreted by the type Ⅲ secretion system in plant-pathogenic bacteria that falls into the Xanthomonas genus, including the rice bacterial blight pathogen. Xops were secreted to the outside of bacterial cells, and then transported to plant cells to play a pathological role. One of these proteins, XopN, secreted by the standard strain PXO99^A of the rice pathogen, has been implicated in the bacterial virulence by subverting plant immunity, but the specificity in the virulence role of XopN is unclear. 【Method】 By using the double crossover homologous-recombination technique, the XopN gene-knockout mutant ∆XopN and genetically complemented strain ∆XopN/XopN were generated under the background of the bacterial wild-type strain PXO99^A. By comparing both recombinant strains with PXO99^A in terms of bacterial multiplication in nutrition broth, the role of XopN in the bacterial multiplication was evaluated. Based on literatures, 14 varieties of rice were chosen for experimental assessments on the contribution of XopN to the spectrum of the bacterial virulence. By quantitative analyses of gene expression, the virulence of XopN was related to the effects of bacterial infection on foliar expression of the OsSWEET11 gene or its homologs in different rice varieties. 【Result】 The bacteria gain better multiplication in the medium with the presence of the XopN gene, in contrast to the gene-knockout mutation, which highly impairs the bacterial propagation level. Based on bacterial populations of PXO99^A, ∆XopN and ∆XopN/XopN multiplied in rice leaves, as well as severities of subsequently developed leaf blight symptoms, the 14 rice varieties fall into two categories. 1) Ten of the rice varieties (IRBB1, IRBB3, IRBB8, IRBB10, IRBB14, IR24, IRBB203, IRBB204, IRBB205 and IRBB211) display similar susceptibility to the bacteria no matter whether the XopN gene is present or not. 2)By contrast, the bacteria depend on XopN to cause strong virulence on rice varieties IRBB208, Asominori and Nipponbare. The bacteria also depend on XopN to perform a relatively low level of virulence on the rice variety IRBB13. In IRBB13 leaves, the virulence role of XopN is coincident with a marked suppression of the recessive resistance gene OsSWEET11/xa13 by the bacterial infection. On the contrary, the bacterial infection causes enhanced expression of the dominant disease-susceptibility gene OsSWEET11/Xa13 in leaves of Nipponbare and enhanced expression of the gene homologs in IRBB208 and Asominori leaves. In essence, the transcriptional promotion or inhibition of the OsSWEET11 homologs is provided by the bacterial strains PXO99^A and ∆XopN/XopN, instead of ∆XopN, suggesting the critical role of XopN in inducing the gene expression. In addition, XopN is also required for the bacteria to effectively induce hypersensitive response in leaves of the non-host plant tobacco. While a high extent of the hypersensitive response is induced by PXO99^A or ∆XopN/XopN strain, the response incurs a substantial reduction by ∆XopN. 【Conclusion】 XopN is a multifunctional effector and plays a virulence role in rice varieties that possess OsSWEET11 or its homologs. XopN is also necessary to the bacterial multiplication and has an additive contribution to the induction of hypersensitive response by the bacteria in a non-host plant.