OsWRKY26 negatively regulates bacterial blight resistance by suppressing OsXa39 expression

Plants are susceptible to infection by various pathogens with high epidemic potential. <i>Xanthomonas oryzae</i> pv<i>. oryzae</i> (<i>Xoo</i>) causes bacterial blight in rice, one of the most significant diseases in both temperate and tropical regions. In this study, we report the identification and characterization of <i>OsWRKY26</i>, a sucrose-inducible transcription factor, that plays a role in the plant defense responses following <i>Xoo</i> infection. We found that mutant plants with defective <i>OsWRKY26</i> showed enhanced defense response specifically to <i>Xoo</i>, indicating that this transcription factor acts as a negative defense regulator. In contrast, mutant plants did not exhibit higher resistance compared to wild-type (WT) plants when infected with the rice blast fungal pathogen <i>Magnaporthe oryzae</i>. Transcriptomic analysis of mutant and WT plants revealed that several pathogen resistance genes were upregulated in mutants. Of these, we selected <i>OsXa39</i> for further analysis. Transient expression experiments in rice protoplasts showed that OsWRKY26 repressed the expression of a <i>Luciferase</i> reporter gene driven by the <i>OsXa39</i> promoter. Chromatin immunoprecipitation analysis revealed that OsWRKY26 binds directly to the promoter region of <i>OsXa39</i>. These findings suggest that OsWRKY26 negatively regulates the defense response during <i>Xoo</i> infection by repressing <i>OsXa39</i> as well as other pathogen-related genes such as <i>OsXa47</i>, <i>OsBBR1</i>, <i>OsRSR1</i>, <i>OsPR1a</i>, <i>OsPR1-11</i>, <i>OsPR2</i>, and <i>OsPR4c.</i>