Phaeocystis microbiome
Oceanic photosymbiosis represents a key ecological and evolutionary process whereby eukaryotic organisms can acquire photosynthesis via symbiotic microalgae, hence contributing to carbon fluxes in oligotrophic waters. Besides the well-studied reef symbioses, planktonic photosymbioses (e.g. Foraminifera, Radiolaria) remain poorly understood. Recent work on the symbiotic association between host radiolaria (i.e. Acantharia) and the endosymbiont haptophyte Phaeocystis sp. shows that photosynthesis and carbon fixation are enhanced in symbiosis. This boosted photosynthesis is very likely beneficial for the host, however, the mechanisms by which photosynthetic products, and in particular sugars that is the main symbiotic currency, are transferred from symbiont to the host cell are unknown, nor if these mechanisms evolved with symbiosis. This study aims at 1) identifying the set of cell membrane transporters in the microalga Phaeocystis sp. constituting the “transportome” 2) test the hypothesis if this microalga exhibits specific genomic footprint of symbiosis (e.g. transporters) compared to non-symbiotic microalgae. We built a “transportome” database consisting of sequence data from genomes and associated in silico characterization (e.g. structure, predicted localization) of a total of ~1400 transporters per species of which ~100 candidate sugar transporters. For instance, we found a higher number of genes belonging to the MST family (sugar transport) and TPT (sugar transport from chloroplast to cytosol) within Phaeocystis genome compared to others species (non-symbiotic haptophytes, and cryptophytes). Next, we analyzed the expression of these genes between symbiotic and non-symbiotic Phaeocystis transcriptomes and found that Glucose transporters are upregulated within symbiosis. This preliminary work highlights some candidate genes that could sustain the sugar transport mechanisms between symbiotic partners and might be key to explain a potential interaction (co)evolution.