OsNPR1-dependent rice genes

NPR1 is a central positive regulator of salicylic-acid (SA)-mediated defense signaling in Arabidopsis. Here, we report characterization of OsNPR1, an Oryzae sativa (rice) ortholog of NPR1, focusing on its role in blast disease resistance and identification of OsNPR1-regulated genes followed by their comparison with NPR1-regulated genes in Arabidopsis. Blast resistance tests using OsNPR1–knockdown and –overexpressing rice lines indicated that OsNPR1 plays an essential role in benzothiadiazole-induced blast resistance. Genome-wide transcript profiling using OsNPR1–knockdown lines revealed that 358 genes out of 1,228 BTH-upregulated genes and 724 genes out of 1,069 BTH-downregulated genes were OsNPR1 dependent with respect to their BTH responsiveness, indicating that OsNPR1 plays a major role in the downregulation. Inspection of OsNPR1-dependent genes revealed that many genes involved in photosynthesis and chloroplastic translation and transcription were downregulated by BTH in an OsNPR1 dependent manner, indicating that photosynthesis and chloroplast activities is coordinately suppressed by OsNPR1 in response to BTH-induced activation of SA-signaling pathway. ABA-responsive genes were also OsNPR1-dependently downregulated, suggesting antagonistic interaction of SA signaling on ABA signaling. None of 11 BTH-upregulated genes for WRKY transcription factors was OsNPR1 dependent, whereas most of those are NPR1-dependently upregulated in Arabidopsis, indicating that the role of OsNPR1 is distinct from that of NPR1 in Arabidopsis. We discuss the significance of OsNPR1-regulated gene expression in SA-regulated defense program and the role of OsNPR1 in rice SA-signaling pathway that is branched to OsNPR1- and rice WRKY45-dependent sub-pathways. mock-treated wild-type (Nipponbare) rice, benzothiadiazole (BTH)-treated wild-type rice, mock-treated WRKY45-knockdown rice (2 lines) and BTH-treated WRKY45-knockdown rice (2 lines) were analyzed in four biological replicates.