Role of OsNPR1 in rice defense program as revealed by genome-wide expression analysis
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NPR1 is a central regulator of salicylic-acid (SA)-mediated defense signaling in Arabidopsis. Here, we report the characterization of OsNPR1, an Oryzae sativa (rice) ortholog of NPR1, focusing on its role in blast disease resistance and identification of OsNPR1-regulated genes. Blast resistance tests using OsNPR1 knockdown and overexpressing rice lines demonstrated the essential role of OsNPR1 in benzothiadiazole (BTH)-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 BTH responsiveness, thereby indicating that OsNPR1 plays a more vital role in gene downregulation. The OsNPR1-dependently downregulated genes included many of those involved in photosynthesis and in chloroplast translation and transcription. Reduction of photosynthetic activity after BTH treatment and its negation by OsNPR1 knockdown were indeed reflected in the changes in Fv/Fm values in leaves. These results imply the role of OsNPR1 in the reallocation of energy and resources during defense responses. We also examined the OsNPR1-dependence of SA-mediated suppression of ABA-induced genes.
KeywordsBenzothiadiazole Blast resistance OsNPR1 NPR1 Photosynthesis Abscisic acid
This work was supported by grants from the Ministry of Agriculture, Forestry, and Fisheries of Japan (Green Technology Project, IP-4006, and Genomics for Agricultural Innovation, PMI-0008). We are grateful for the excellent technical support provided by Ms. M. Ishikawa and Ms. T. Yasuhara. We thank Prof. K. Shimamoto for providing the RNAi vector pANDA; Dr. S. Toki and Ms. K. Ono, for technical advice; and Mr. T. Numa, for advice on microarray data analysis. We also thank the Rice Genome Resource Center at NIAS for the use of the rice microarray analysis system, as well as Dr. Y. Nagamura and Ms. R. Motoyama for their technical support.
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