Figure 1.

The regulon. In experiments involving Blumeria graminis f. sp. hordei, Erysiphe cichoracearum, Golovinomyces orontii, a structural, biochemical and physiological apparatus referred to as the regulon has been designated to refer to a defense apparatus involving the PENETRATION1-3 proteins. (A) The spore has germinated producing a neck that is attached to the appressorium which begins to push through the cell wall resulting in a plant cell response that leads to callose deposition. (B) The haustorium develops and pushes through the callose during a susceptible response. (C) Golgi-drived vesicles deliver the PEN1-3 proteins to the infection site, leading to a successful defense response that includes increased deposition of callose.^{5,6,8,15,16,254-266}