The Crippled Growth epigenetic cell degeneration of Podospora anserina, an overview

Fungi frequently undergo phenotypic changes. In the case of filamentous fungi, the change often manifests itself as sectors of different morphology and color on the thallus. These changes may have a genetic or an epigenetic origin. For 20 years, my lab has been studying a complex and intriguing phenotypic change: the Crippled Growth (CG) cell degeneration of Podospora anserina. Early analysis revealed CG to be epigenetic and linked to the spreading in hyphae of a cytoplasmic and infectious factor. This factor can be at will induced and cured by simple stimuli, stationary phase and stress, respectively. Through a classical genetic approach, i.e., the search of mutants altering CG, we have been able to show that the degeneration likely stems from the abnormal activation of the “Cell Wall Integrity” MAP kinase cascade. I will summarized what we know about CG, especially I will present our analyses of the IDC mutant affected in the MASTRINO complex that are unable to undergo CG, but also that of what is likely the master locus enabling this cell degeneration by promoting the growth- and stress-regulated misactivation of the MAP kinase cascade.