NPR1 differentially interacts with members of the TGA/OBF family of transcription factors that bind an element of the PR-1 gene required for induction by salicylic acid

NPR1 is a critical component of the salicylic acid (SA)mediated signal tran sduction pathway leading to the induction of defense genes, such as the pat hogenesis-related (PR)-1 gene, and enhanced disease resistance. Using a yea st two-hybrid screen, we identified several NPR1-interacting proteins (NIPs ), Two of these NIPs are members of the TGA/OBF family of basic leucine zip per (bZIP) transcription factors; this family has been implicated in the ac tivation of SA-responsive genes, including PR-1, Six TGA family members wer e tested and shown to differentially interact with NPR1: TGA2 and TGA3 show ed strong affinity for NPR1; TGA5 and TGA6 exhibited weaker affinity; and T GA1 and TGA4 displayed little or no detectable interaction with NPR1, respe ctively. Interestingly, the amino-termini of these factors were found to de crease their stability in yeast and differentially affect their apparent af finity toward NPR1, The interacting regions on NPR1 and the TGA factors wer e also defined. Each of four point mutations in NPR1 that disrupt SA signal ing in Arabidopsis completely blocked interaction of NPR1 with TGA2 and TGA 3, TGA2 and TGA3 were also found to bind the SA-responsive element of the A rabidopsis PR-1 promoter. These results directly link NPR1 to SA-induced PR -1 expression through members of the TGA family of transcription factors.