Ultrastructural and transcriptional changes during a giant virus infection of a green alga

The genome of Oceanusvirus kaneohense isolate, Tetraselmis virus 1 (TetV-1), was previously sequenced, but little was known about its infection cycle. We determined the eclipse period (4-8 h), latent period (16 h), and burst size (~1000), and observed ultrastructural changes in the host during infection. Putative viral factories and inclusion bodies appear in the cytoplasm by 8 and 16 h post-infection, respectively. Of 830 viral transcripts detected, those related to transcription, DNA synthesis, and host immune repression appeared earlier (0.25 and 4 h), and virus structural genes appeared later (8-16 h). Host lipid metabolism and endocytosis-related transcripts were upregulated during the early phase, while protein modification genes were downregulated. In the later stages, host transcripts associated with basic cellular processes were relatively more common, while developmental genes became less so. Many highly expressed host and virus genes were of unknown function, highlighting a need for additional functional studies.