Figure 6.

Proposed Model for the Regulatory Mechanism of TGA2 in SAR-Related Gene Expression.

(A) In wild-type plants, NPR1 forms complexes with TGA2 and other TGA factors (TGA?). Under noninducing conditions, these complexes are unable to bind to DNA. Upon SAR induction (+SA), more NPR1 becomes available to form the NPR1-TGA2 complex. Through an unknown mechanism, NPR1 enhances the DNA binding activity of TGA2, leading to PR gene induction.

(B) In an npr1 mutant, the NPR1–TGA2 interaction is disrupted, so TGA2 cannot bind to DNA. Some TGA factors (TGA?) may be able to bind to DNA in the absence of NPR1, but they are not active in inducing PR gene expression.