Different patterns of gene expression in rice varieties undergoing a resistant or susceptible interaction with the bacterial leaf streak pathogen
The rice line carrying the nonhost gene Rxo1, which was cloned from maize, exhibits a rapid hypersensitive response (HR) to Xanthomonas oryzae pv. oryzicola (Xoc). In this study, a microarray experiment was carried out to analyze the genome-wide gene expression responses to Xoc at the early stage in the rice transgenic line and its wild type. 175 and 379 differentially regulated genes (DRGs) were detected in 9804-Rxo1 and 9804 at 36 h post-inoculation (hpi), respectively. The patterns of DRGs induced by Xoc in the transgenic rice line and its wild type were distinctly different: 92.00% of the DRGs were up-regulated in inoculated 9804-Rxo1 and 48.22% of the DRGs were sorted as defense-related genes. In contrast, 40.69% of the DRGs were up-regulated in inoculated 9804 and 40.00% were sorted as injury-induced genes. Some genes specifically up-regulated in infected 9804-Rxo1 were defenserelated, including the genes encoding pathogenesis-related protein, terpene synthase family, transcription factors (TFs) AP2 domain containing protein, myb-like deoxyribonucleic acid (DNA)- binding domain containing protein, and C2H2-type zinc-finger transcription factors. Six peroxidase (POD) genes were significantly up-regulated and POD activity consistently rose in the inoculated 9804- Rxo1, whereas seven POD genes were down-regulated in its wild type, indicating that POD may also play a role in the complex process of resistant response to Xoc in the transgenic line. Instead of focusing only on the R-gene-mediated defense, this study also discusses the susceptible response in the wild types to virulent pathogen infection in transcription level.
Key words: Rice bacterial leaf streak, nonhost resistance, expression profile, Rxo1.