WRKY70 prevents axenic activation of plant immunity by direct repression of SARD1

Summary SARD 1 is an activator of plant immunity that promotes production of the hormone salicylic acid ( SA ) and activation of defense gene expression. SARD 1 itself is strongly inducible by infection. Here, we investigated the transcriptional control of SARD 1 . We used yeast one‐hybrid assays to identify WRKY 70. The WRKY 70 binding site was defined using electrophoretic mobility shift assays, and its importance was investigated using an Arabidopsis thaliana protoplast system. The effect of wrky70 mutations was studied by measurements of pathogen growth, SA concentrations, and gene expression by RNA ‐seq. WRKY 70 binds to a GACTTTT motif in the SARD 1 promoter in yeast and Arabidopsis protoplasts. Plants with wrky70 mutations have elevated expression of SARD 1 in the absence of pathogens, but not when infected. Expression profiling revealed that WRKY 70 represses many pathogen‐inducible genes in the absence of pathogens, yet is required for activation of many other pathogen‐inducible genes in infected plants. The GACTTTT motif is enriched in the promoters of both these gene sets, and conserved in SARD 1 orthologs within the Brassicaceae . WRKY 70 represses SARD 1 by binding the motif GACTTTT in the absence of pathogens. Conservation of the WRKY 70 binding among the Brassicaceae suggests that WRKY 70 repression of SARD 1 is important for fitness.