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

• 
  

• 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 (电泳迁移率变动分析法), and its importance was investigated using an Arabidopsis thaliana protoplast system (原生质体系统). 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.

SARD1是植物免疫的激活子，会促进植物激素水杨酸SA的产量，激活防御基因的表达。SARD1基因本身是受到侵染的强烈诱导。本文研究了SARD1基因的转录调控。

作者利用了酵母单杂试验来鉴定WRKY70。电泳迁移率变动分析法鉴定WRKY70的结合位点，并利用拟南芥的原生质体系统来研究其重要性。通过对wrky70突变体上病原菌的生长、SA浓度及基因表达研究WRKY70基因的功能。

在酵母和拟南芥的原生质体中，WRKY70会结合到SARD1基因启动子的GACTTTT基序。wrky70突变体植株会在病原菌未侵染时提升SARD1基因的表达，反而在病原菌侵染时不提升SARD1基因的表达。基因表达谱研究显示WRKY70会在病原菌未侵染时抑制许多病原菌诱导基因的表达，WRKY70基因在侵染植物中其它许多病原菌诱导基因的激活起作用。在这些基因中的启动子区富含GACTTTT基序，并且在十字花科植物SARD1同源基因之间十分保守。

研究方向：拟南芥防御响应基因组学研究。

doi: 10.1111/nph.14846