Plasmogamy

Plasmogamy is the initial stage of cytoplasmic fusion in many sexually reproducing fungi and some other organisms. It involves the fusion of the cytoplasm from two genetically compatible haploid cells, producing a cell that contains two genetically distinct haploid nuclei. This pairing can result in a dikaryon (two nuclei per cell) or a more general heterokaryon, in which the nuclei remain separate but share the same cytoplasm. Unlike karyogamy, plasmogamy does not immediately fuse the nuclei.

In the life cycles of many basidiomycete and ascomycete fungi, plasmogamy is followed by a prolonged dikaryotic stage, during which the two haploid nuclei divide without fusing. The dikaryotic mycelium often forms the dominant vegetative phase and leads to the development of fruiting bodies in which karyogamy eventually occurs, producing a diploid zygote that undergoes meiosis to form haploid spores. In some organisms, plasmogamy can proceed rapidly to karyogamy, but in most fungi the two nuclei remain separate for an extended period.

Mechanistically, plasmogamy is typically driven by mating-type recognition and pheromone signaling that promotes cytoplasmic fusion between compatible partners. The resulting cytoplasm may exchange organelles and metabolites, while the nuclei remain distinct until subsequent nuclear fusion occurs. The process is a key step in sexual reproduction and genetic recombination, contributing to genetic diversity and ecological adaptability in fungal populations.