SARD1 is an activator of plant immunity that promotes production of the hormone salicylic acid (SA) and activation of defense gene expression. SARD1 itself is strongly inducible by infection. Here, we investigated the transcriptional control of SARD1. We used yeast one-hybrid assays to identify WRKY70. The WRKY70 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. WRKY70 binds to a GACTTTT motif in the SARD1 promoter in yeast and Arabidopsis protoplasts. Plants with wrky70 mutations have elevated expression of SARD1 in the absence of pathogens, but not when infected. Expression profiling revealed that WRKY70 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 SARD1 orthologs within the Brassicaceae. WRKY70 represses SARD1 by binding the motif GACTTTT in the absence of pathogens. Conservation of the WRKY70 binding among the Brassicaceae suggests that WRKY70 repression of SARD1 is important for fitness.
Bibliographical noteFunding Information:
We thank for Dr Thomas Eulgem for wrky70-1 and wrky70-3 seeds, Dr Fabian Machens for helpful information about purifying WRKY70, Dr Bill Gray for the yeast strain YM4271, Dr Nakagawa Tsuyoshi for pUGW2 and pUGW435 vectors, Dr Bo Xia for help on bioinformatics analysis, and the University of Minnesota Genomics Center for generating RNA-seq data. This work was supported by grants IOS-1353854 to J.G. and IOS-1121425 and MCB-1518058 to F.K. from the National Science Foundation.
© 2017 The Authors. New Phytologist © 2017 New Phytologist Trust
- Pseudomonas syringae
- calmodulin-binding protein
- salicylic acid (SA)
- transcription factors