WRKY Transcription Factor Functions as a Transcriptional Regulator of Xylanase Inhibitor RIXI, Involved in Rice Disease Resistance to Magnaporthe oryzae

Xylanase inhibitors are known to play important roles in response to fungal pathogens attack. WRKY transcription factors are also involved in plant defence against pathogens. However, whether WRKY transcription factors interacting with rice xylanase inhibitor RIXI remains unknown. 13 W-boxes, binding sites for WRKY transcription factors were found in RIXI promoter sequence of rice by analyzing RIXI promoter. ChIP-PCR analysis and dual luciferase reporter system assay were used to identify interaction between xylanase inhibitor RIXI and WRKY transcription factors. Results showed OsWRKY6 and OsWRKY46 directly bound to RIXI promoter and regulated RIXI expression differently. Over-expressing OsWRKY6 and OsWRKY46 transgenic plants were achieved, and OsWRKY6 and OsWRKY46 overexpressed transgenic lines showed higher expression levels of RIXI and higher resistance to Magnaporthe oryzae G11 ( M. oryzae G11) compared to wild type (WT) . Increased RIXI expression in OsWRKY6 and OsWRKY46 overexpressed transgenic lines was accompanied by up-regulation of pathogenesis-related genes ( PR genes ). Moreover, higher levels of H 2 O 2 and higher activities of antioxidant enzymes were found in transgenic lines compared to WT plants. Results indicated that over-expression of OsWRKY6 and OsWRKY46 in transgenic lines maybe enhanced rice disease resistance by regulating RIXI expression.