The Acantharia-Phaeocystis symbiosis: an investigation of eukaryotic photosymbiosis and its ecological role in oligotrophic surface water

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During the fiscal year 2019 I completed my PhD thesis and thesis defense. I presented my final thesis chapter as a poster at the Ocean Sciences Meeting in California. In addition, I submitted 3 first author manuscripts for publication; they are under review and are openly available as preprints on bioRxiv. The chapter investigated gene expression in symbiotic Phaeocystis (Haptyophyta) while living inside Acantharian (Rhizaria) hosts. I performed single-holobiont RNA-seq with individual acantharian hosts. I then performed RNA-seq with 3 biological replicates each from two cultured Phaeocystis species, which I used to create reference transcriptomes and map symbiont transcripts from the holobionts. I then performed differential expression analyses for the two symbiont species. Results showed that symbionts upregulated photosynthesis and gene expression, but down regulated DNA replication and cell cycle progression. Importantly, symbiont gene expression did not suggest that symbionts were at all nutrient limited, which is a common method hosts use to limit symbiont cell division. Instead, hosts must be deploying a nutrient independent control mechanism.