A permeable cuticle is associated with the release of reactive oxygen species and induction of innate immunity

This study provides an explanation for the strong resistance to B. cinerea observed in wounded plants or plants with cuticular defects. We have observed that a production of ROS and a permeable cuticle is common to all these situations. ROS, that include hydrogen peroxide, are known inducers of resistance and can also act directly against the invading fungus. Degradation of the cuticle by exposure to cutinase also results in the production of ROS and resistance. These observations lead to a model where the cuticle plays a central role as a barrier against water-soluble elicitors from the surface. Under normal circumstances, the cuticle does not allow the passage of elicitors and no responses are induced. Under conditions where the cuticular barrier is broken, ROS and resistance are induced. This illustrates why plants that are in fact permanently exposed to potential elicitors do not constantly induce immune responses: this only takes place once the cuticle has been permeabilized, for example after an infection with a pathogen. This study also demonstrates how a cuticle-degrading pathogen avoids the generation of ROS by producing an effector that interferes with ROS production. Removal of this effector restores both ROS and resistance.