Fig. 3.

Vegetative incompatibility. a Hyphae of vegetatively incompatible filamentous fungi grow towards each other by chemotaxis. b Hyphal fusion occurs, resulting in a heterokaryon. c Expression of incompatible het genes in the heterokaryon leads to sealing of septal pores, autophagy, and programmed cell death. Vacuolization and the formation of additional septa (not pictured) also occur. Autophagy (represented by small circles in the cytoplasm of the heterokaryon) may prevent the spread of pro-death signals and is not thought to contribute to the cell death process. Thinning of the heterokaryotic filament accompanies cell death