Direct visualization of protein interactions in plant cells

The protein NPR1/NIM1 is required for the induction of systemic acquired re sistance (SAR) in plants and has been shown to interact with members of the TGA/OBF family of basic leucine zipper (bZIP) transcription factors. Howev er, to date, there is no method available to monitor such interactions in p lant cells. We report here an in vivo protein fragment complementation assa y (PCA), based on association of reconstituted murine dihydrofolate reducta se (mDHFR) with a fluorescent probe to detect protein-protein interaction i n planta. We demonstrate that the interaction between Arabidopsis NPR1/NIM1 and the bZIP factor TGA2 is induced by the regulators of SAR, salicylic ac id (SA), and its analog 2,6-dichloroisonicotinic acid (INA) with distinct s pecific specific responses. Furthermore, the induced interaction is localiz ed predominantly in the nucleus. Protein fragment complementation assays co uld be of value to agricultural research by providing a system for high-thr oughput biochemical pathway mapping and for screening of small molecules th at modulate protein interactions.