Molecular characterization of Oryza sativa WRKY6, which binds to W‐box‐like element 1 of the Oryza sativa pathogenesis‐related (PR) 10a promoter and confers reduced susceptibility to pathogens

Summary WRKY proteins are transcription factors ( TF s) that regulate the expression of defense‐related genes. The salicylic acid ( SA )‐inducible Oryza sativa WRKY6 (OsWRKY6) was identified as a positive regulator of Oryza sativa pathogenesis‐related 10a ( OsPR10a ) by transient expression assays. A physical interaction between Os WRKY 6 and W‐box‐like element 1 ( WLE 1), which positively regulates Os PR 10a/ probenazole induced protein 1 expression, was verified in vitro . Several pathogenesis‐related ( PR ) genes were constitutively activated, including Os PR 10a , and transgenic rice ( Oryza sativa ) plants overexpressing (ox) Os WRKY 6 exhibited enhanced disease resistance to pathogens. By contrast, PR gene induction was compromised in transgenic Os WRKY 6 ‐ RNA i lines, suggesting that Os WRKY 6 is a positive regulator of defense responses. Os WRKY 6‐ox lines displayed leaf lesions, and increased Os WRKY 6 levels caused cell death. Salicylic acid ( SA ) concentrations were higher in Os WRKY 6 ‐ox lines than in wild‐type ( WT ) plants, and transcript levels of Oryza sativa isochorismate synthase 1 ( OsICS1 ), which encodes a major enzyme involved in SA biosynthesis, were higher in Os WRKY 6 ‐ox lines than in WT . Os WRKY 6 directly bound to the Os ICS 1 promoter in vivo . This indicates that Os WRKY 6 can directly regulate Os ICS 1 expression and thereby increase SA concentrations. Os WRKY 6 autoregulates its own expression. Os WRKY 6 protein degradation is possibly regulated by ubiquitination. Our results suggest that Os WRKY 6 positively regulates defense responses through activation of Os ICS 1 expression and Os WRKY 6 stabilization.