Plants are continuously exposed to pathogen challenge. The most common defense response to pathogenic microorganisms is the nonhost response, which is usually accompanied by transcriptional changes. In order to identify genes involved in nonhost resistance, we evaluated the tobacco transcriptome profile after infection with Xanthomonas axonopodis pv. citri (Xac), a nonhost phytopathogenic bacterium. cDNA-amplified fragment length polymorphism was used to identify differentially expressed transcripts in tobacco leaves infected with Xac at 2, 8 and 24 h post-inoculation. From a total of 2087 transcript-derived fragments (TDFs) screened (approximately 20% of the tobacco transcriptome), 316 TDFs showed differential expression. Based on sequence similarities, 82 differential TDFs were identified and assigned to different functional categories: 56 displayed homology to genes with known functions, 12 to proteins with unknown functions and 14 did not have a match. Real-time PCR was carried out with selected transcripts to confirm the expression pattern obtained. The results reveal novel genes associated with nonhost resistance in plant-pathogen interaction in tobacco. These novel genes could be included in future strategies of molecular breeding for nonhost disease resistance. (C) 2010 Elsevier GmbH. All rights reserved.