Protoplasmic Incompatibility and Cell Lysis in PODOSPORA ANSERINA. I. Genetic Investigations on Mutations of a Novel Modifier Gene That Suppresses Cell Destruction.

In Podospora anserina, protoplasmic incompatibility (a phenomenon that prevents heterokaryon formation because of the destruction of the fused cells) can be studied in homokaryotic strains that combine nonallelic incompatibility genes or carry mutations at the lys loci. In these strains cell destruction occurs early in development and is associated with an arrest of growth.-From the self-lysing strains lysA(1) and RV (R and V are nonallelic incompatibility genes) mutations have been selected that suppress the self-lysing trait, i.e., that prevent cell destruction and remove growth inhibition. Some of them were derived from a novel modifier locus, modC, located near the mating-type locus.-In C/D and C/E incompatibility systems, modC mutations, which per se have no obvious effect, were considered in addition to mutations in the previously identified modifier loci, modA and modB. The demonstration of a functional interdependence among the three mod genes suggested that modC is not the structural gene for the protease associated with cell lysis, but is involved, like modA and modB, in its control.-All three modC mutant strains investigated exhibit defects in the formation of protoperithecia, suggesting that the modC gene function is essential to the occurrence or development of the female organs. This is the third argument that supports the hypothesis ( Boucherie, Bégueret and Bernet 1976) that protoplasmic incompatibility and female organ formation might be related phenomena.