Vegetative cell fusion and a new stage in the life cycle of the Aphelida (Opisthosporidia)

Abstract The aphelids, intracellular parasitoid of algae, play significant role in the ponds communities regulating the algae blooms. They represent a large cluster of OTUs sister to Fungi at the molecular phylogenetic tree sharing a common ancestor with fungi. Their vegetative life cycle being similar to that of chytridiomycetes includes opisthokont uniflagellar zoospores, cysts, phagotrophic intracellular stage, and multinuclear plasmodium producing zoospores. The sexual part of life cycle is not known, and, as we can see now, the asexual part is also understudied. We have found in the Aphelidium insulamus and other ahelid species a new stage – big multiflagellar, or amoeboid cells, which can be considered both, the result of zoospore fusion, or the remnant of plasmodium after zoospore formation. A study of this phenomenon lead us to the conclusion, that after multicellular infection the trophic stages of different parasitoids fuse in one plasmodium having different sorts of nuclei. Some of them become the nuclei of zoospores, while the others left in the remnant of plasmodium, which becomes a monster. The families of protein encoded genes involved in the vegetative cell fusion was also discussed.