Figure 4:

A Model for the Regulation and Activation of R-Protein Mediated Defense Signaling in Arabidopsis.

A) In the absence of a pathogen, R-proteins are held in an inactive state. This conformation is the result of protein-proteins interaction(s), and as a consequence of these associations, binding of ATP/GTP to the NB domain is blocked.

B) Following perception of the pathogen, via the activity of secreted effector molecules, an induced conformational change in the R-protein complex is induced. This change results in a possible shift in the stoichiometry of protein-protein interactions, leading to the binding of ATP/GTP to the R-protein NB domain.

C) Once a pathogen effector is recognized, the activation of ETI results in the initiation of defense signaling, ultimately leading to the abrogation of pathogen growth. Once perturbations to the R-protein surveillance system are no longer perceived, the system resets back to the resting state depicted in “A”.