Heterokaryon incompatibility in fungi - More than just another way to die

In filamentous fungi heterokaryon (vegetative) compatibility is regulated by a number of different loci. Vegetative incompatibility is most often detected as the inability to form a prototrophic heterokaryon under forcing conditions, or as the formation of a barrage when two incompatible strains interact. Vegetative compatibility has been used as a multilocus phenotype in analysis oi fungal populations. In some highly clonal populations the vegetative-compatibility phenotype is correlated with pathogenicity. The molecular basis for vegetative compatibility is not well understood. Four her loci have been cloned from Neurospora crassa or Podospora anserina, but no two are alike and it is clear that the her genes themselves do not encode the gene products that are directly responsible for cell death. We suggest that a broader view of vegetative compatibility would include genes that are responsible for prefusion, fusion, and postfusion activities. Postfusion activities could include the fungal apoptotic apparatus since microscopic observations of cell death resemble those in higher plants and animals.