Figure 7.

Working Model for the Regulation of TGA2 by NPR1 and Stoichiometry of the TGA2-NPR1 Enhanceosome.

Left panel: In untreated cells, where NPR1 does not interact with TGA2, TGA2 would form an oligomer capable of binding to its cognate TGACG sequence in the promoter of target genes. This oligomer would repress transcription by a mechanism yet to be identified. Oligomerization of TGA2 on DNA involves the leucine zipper and the N-terminal repression domain. Right panel: After a rise in SA, the NPR1 BTB/POZ domain (POZ) would either assist in disassembling the TGA2 oligomer or assist in recruiting TGA2 dimers to cognate DNA, while excluding TGA2 tetramers and oligomers from binding DNA. The TGA2-NPR1 enhanceosome is likely to have a stoichiometry of 2:2 (TGA2:NPR1). The BTB/POZ domain of NPR1 dimerizes and interacts with the N-terminal repression domain of TGA2 (gray) to mask its capacity to form an oligomer on DNA. The ankyrin repeats (ANK) are the major interfaces stabilizing the TGA2-NPR1 complex, while the C-terminal region of NPR1 contains the transactivation domain (TA) of the enhanceosome.