Arabidopsis WRKY50 and TGA Transcription Factors Synergistically Activate Expression of PR1

Arabidopsis is a salicylic acid (SA) inducible marker gene for systemic acquired resistance (SAR). However, the regulation of in plants is poorly understood. In this study, we showed that AtWRKY50 transcription factor binds to two promoter elements of via its DNA binding domain. Interestingly, the DNA-binding sites for AtWRKY50 deviate significantly from the consensus WRKY binding W-box. The binding sites are located in close proximity to the binding sites for TGA transcription factors. Transactivation experiments in Arabidopsis protoplasts derived from wild type, and mutant plants indicated that AtWRKY50 alone was able to induce expression of a ::β- (GUS) reporter gene, independent of TGAs or NPR1. However, co-expression of TGA2 or TGA5 with AtWRKY50 synergistically enhanced expression to high levels. Yeast-2-hybrid assays and bimolecular fluorescence complementation (BiFC) experiments revealed that AtWRKY50 could interact with TGA2 and TGA5. Using electrophoretic mobility shift assays (EMSA) it was established that AtWRKY50 and TGA2 or TGA5 simultaneously bind to the promoter. Taken together, these results support a role of AtWRKY50 in SA-induced expression of . AtWRKY50 specifically binds to LS10 region of promoter and interacts with TGAs to synergistically activate expression.