Fate of Parasite and Host Organelle DNA during Cellular Transformation of Red Algae by Their Parasites

The transfer of a nucleus into a cytoplasm of a genetically foreign cell and its subsequent multiplication in the cytoplasm of this cell characterize most parasitic red algal species and their interactions with specific red algal hosts. Nuclei enter the host's cytoplasm upon cell fusion of parasite and host cell; here, they replicate, are spread to contiguous host cells, and ultimately are packaged into spores that reinfect other host thalli. In this study, we examined whether the proplastids and mitochondria that occur in these red algal adelphoparasites are acquired from their host or whether they are unique to the parasite and are brought into the host along with the parasite nucleus. To establish their origins and fates, plastid and mitochondrial restriction fragment length polymorphisms (RFLPs) of parasite cells were compared with those of their host plastid and mitochondrial DNA in three host and parasite pairs. For plastids, no RFLP differences were found between hosts and parasites, supporting an earlier conclusion, based on microscopic studies, that the proplastids of parasites are acquired from their hosts. For mitochondria, characteristic RFLP differences were detected between host and parasite for two of the pairs of species but not for the third. Evidence of the evolutionary difference between hosts and their parasites was shown by RFLP differences between nuclear ribosomal repeat regions.