The immune systems that plants use to defend against pathogens normally deflect attack. However, Lorang et al. have identified a rearguard susceptibility that a necrotrophic fungus exploits. The fungal toxin victorin interacts with the defense protein LOV1 in Arabidopsis and activates it, but the result, counterintuitively, is that the plant succumbs to the disease rather than fighting it off. What seems to be happening is that victorin targets a thioredoxin that regulates the systemic acquired resistance pathway. That interaction triggers activity of LOV1, which in turn incites cell death. The invading fungus then benefits from the ready access to dead cells.
J. Lorang, T. Kidarsa, C. S. Bradford, B. Gilbert, M. Curtis, S.-C. Tzeng, C. S. Maier, T. J. Wolpert, Tricking the guard: Exploiting plant defense for disease susceptibility. Science 338, 659–662 (2012). [Abstract] [Full Text]