Podospora anserina mutations inhibiting several developmental alternatives and growth renewal.

A mutation (modG) was selected on the basis of the suppression of a defect resulting from a mutation of modD gene. The modG mutation shows the same developmental consequences as modD mutations: the absence of protoperithecia and aerial hyphae, the non-renewal of growth from stationary cells and the non-germination of ascospores. Investigations of heterokaryotic mycelia showed that the action of modD and modG mutations on the formation of protoperithecia and aerial hyphae is autonomous. Furthermore, taking advantage of the thermosensitivity of a modD mutation, it was shown that the mutations have no incidence on cell differentiation prior to the achievement of stationary physiology. These findings lead to suggest the existence, in Podospora anserina, of a stage of cell totipotency, which we call the switch stage, that derives from the stationary state through the action of modD and mode genes. Accordingly, the switch stage would be the intermediate in the process of growth renewal from stationary cells and the basic stage for the selection of the developmental alternatives (aerial hyphae, protoperithecia ...) of Podospora mycelia.