Vesicle trafficking pathways in defence-related cell wall modifications - papillae and encasements.

Filamentous pathogens that cause plant diseases such as powdery mildew, rust, anthracnose, and late blight continue to represent an enormous challenge for farmers worldwide. Interestingly, these pathogens, although phylogenetically distant, initiate pathogenesis in a very similar way by penetrating the cell wall and establishing a feeding structure inside the plant host-cell. To prevent pathogen ingress, the host-cell responds by forming defense structures known as papillae and encasements that are thought to mediate pre- and post-invasive immunity, respectively. This form of defense is evolutionarily conserved in land plants and is highly effective and durable against a broad selection of non-adapted filamentous pathogens. As most pathogens have evolved strategies to overcome the defenses of only a limited range of hostplants, the papilla/encasement response could hold the potential for becoming an optimal transfer of resistance from one plant species to another. With this review I will try to lay out the current knowledge on the involvement of membrane trafficking that forms these important defense structures and highlight some of the questions that still need to be solved.