Although the potential of nonhost resistance in protecting crops from plant diseases is well-documented, the underlying mechanism of nonhost resistance to Xoo, which causes a serious disease of rice, remains unclear. One aim of this study was to establish an efficient system to screen for genes required for nonhost resistance to Xoo. Thus it was essential to identify a suitable plant that was a nonhost of Xoo, and N. benthamiana was selected based on several considerations. N. benthamiana is easily grown, produces seed quickly, is amenable to manipulation, and a draft of the genome has been recently released (http://solgenomics.net/). The pathogen Xoo has a narrow host range that consists of rice, several species of wild rice, and a number of graminaceous weeds [11]. Thus, the plants infected by Xoo are not related to N. benthamiana and the latter can be regarded as a nonhost of Xoo. Inoculation of a given pathogenic bacterium into nonhost plants is generally accompanied by nonhost resistance and a macroscopically visible HR [36]–[37].