Rice blast is an economically important disease caused by the fungus Magnaporthe grisea, which enters leaves by developing specialized structures called appressoria. Veneault-Fourrey et al. show that during invasion, the fungus undergoes a form of programmed cell death that involves autophagy. Thus, fungal pathogens can use cell death for cellular differentiation and remodeling during host infection. Fungal virulence, the ability of opportunistic fungal pathogens to thrive in mammals, is associated with a transformation from a filamentous, pseudohyphal form that grows at 25°C into a yeast form at 37°C. Using the plant pathogen Agrobacterium tumefaciens as a tool for T-DNA insertional mutagenesis, Nemecek et al. identified mutants that locked the organism in the filamentous form. One mutant that could not make the yeast form also showed defects in cell-wall formation, sporulation, and expression of virulence factors. The defect lay in a gene encoding a histidine kinase, which appeared to be the global regulator for morphological switching and virulence in several species of dimorphic fungi.
C. Veneault-Fourrey, M. Barooah, M. Egan, G. Wakley, N. J. Talbot, Autophagic fungal cell death is necessary for infection by the rice blast fungus. Science 312, 580-583 (2006). [Abstract] [Full Text]