Fig. 7: Schematic comparison of prey–predator, transient endosymbiotic (kleptoplasty), and permanent endosymbiotic relationships.

Predators start digesting algae immediately after phagocytic ingestion of algae (left). Kleptoplastic species retain the ingested algae for days to weeks in the cell before digesting them in some cases, including that of N. aeruginosum, with the nucleus of the algae (middle). The present study shows that the ingested nucleus is polyploidized in the host cell, which increases mRNA levels. The ingested nucleus almost loses transcriptional regulation. These changes were also common to the course of establishment of nucleomorph and chloroplast (also other types of plastids) as obligate endosymbionts in eukaryotes (right).