Figure 1. Schematic representation of the events occurring in the cell wall during a fungal attack of a plant tissue.

Polygalacturonase (PG) secreted by the pathogen breaches the wall by degrading the pectin component. In the presence of the inhibitor PGIP degradation is slowed down and the formation of signal molecules (OG) for the activation of immunity is favoured. Expression under a pathogen-inducible promoter of a PG-PGIP fusion protein named OG-machine enhances the accumulation of OG and immunity.