IN PODOSPORA-ANSERINA, PROTOPLASMIC INCOMPATIBILITY GENES ARE INVOLVED IN CELL-DEATH CONTROL VIA MULTIPLE GENE INTERACTIONS

Protoplasmic incompatibility in Podospora anserina manifests itself as the destruction of cells following anastomosis between hyphae of unlike genotypes. Non-allelic gene interactions between the genes of at least nine loci are involved in this phenomenon. An investigation of five of these loci (c, d, e, r and v) shows that the corresponding genes are components of a genetic system that controls the growth of mycelium aerial structures (especially protoperithecia and perithecia) via c/d, c/e and r/v gene interactions. Perithecium development, after fertilization, depends on the action of the c and v genes in developing perithecia on their corresponding d/e and r genes in the vegetative cells. An analysis of the life span of stationary phase cells showed that the same gene interactions are involved in the premature death of cells which is a response to the genetic conditions that cause perithecium development. These results support the idea that protoplasmic incompatibility is a deviant expression of the cell death associated with the growth of mycelial aerial structures, especially perithecia. This means, in particular, that the degradative activities (especially proteases) associated with protoplasmic incompatibility are responsible for cell death. It is therefore concluded that the genes of the c-v incompatibility loci are part of a multiple gene system. This system regulates, in association with protoperithecium and perithecium development, via the action of two regulatory genes, the production of catabolite activities that convert vegetative cells from quiescence to a source of nutrient available to the female developmental cycle until spore production.