Cell wall responses to biotrophic fungal pathogen invasion

To a plant the surrounding environment is filled with microbial organisms looking to take advantage of the bountiful resources held within. In order for a pathogen to access the internal nutrients it must gain entry through the plant cell outer layers that consist of the cuticular wax and the plant cell wall. This barrier is a complex structure composed of diverse waxes, lipids, polysaccharides, proteins, lignin, and antimicrobial compounds and plays many crucial roles during plant defence, growth, and development. We now have more evidence than ever about the dynamic nature of the cell wall providing various interaction-dependent passive and active defence responses, hence justifying a necessity of evolving such a complex structure. Here we summarise the current understanding of this multi-layered defence system, using the biotrophic interaction between barley and the causal agent of powdery mildew, Blumeria graminis f. sp. hordei (Bgh).