Abstract
Radiolarians are a group of ubiquitous, yet poorly understood, large protists that often harbor photosymbionts. We studied the solitary radiolarian Thalassicolla nucleata by analyzing the transcriptome of its holobiont. We found that T. nucleata contained two dinoflagellate symbionts, one photosymbiont Brandtodinium sp., and one putative Peridiniales parasite. Through comparisons of gene expressions of Brandtodinium sp. and those of a close relative from a free-living culture, we found that the Brandtodinium sp. maintained its photosynthetic activities, but altered its carbon metabolism dramatically in hospite. Gene expression data also suggested carbon and nitrogen exchange between the host and photosymbiont and that lectin-glycan interaction might play an important role in host-symbiont recognition.
Highlights
Radiolarians are single-celled, heterotrophic protists from the phylum Retaria of the supergroup Rhizaria
It is estimated that roughly half of the radiolarian species in oceanic surface waters harbor photosynthetic symbionts, and primary production by the symbionts can account for up to 80% of the carbon budgets of the holobionts (Caron et al, 1995)
Solitary radiolarians were individually transferred into a multi-welled culture dish filled with 0.22 um-filtered seawater, incubated for 12 h, during which time they were moved with Agilent 2100 Bioanalyzer using a High Sensitivity DNA chip and quantified with Qubit 3.0 DNA High Sensitivity Assay
Summary
Radiolarians are single-celled, heterotrophic protists from the phylum Retaria of the supergroup Rhizaria They are abundant and widespread throughout broad expanses of pelagic oceanic ecosystems, and can account for a significant portion of the planktonic community (Dennett et al, 2002; Biard et al, 2016). Radiolarians containing photosynthetic symbionts have been shown to have exceptionally high rates of photosynthesis, and it has been demonstrated that photosynthate from the photosymbionts is translocated to the host cytoplasm (Anderson et al, 1983; Caron et al, 1995). These studies imply that symbiont-derived photosynthates are an important source of nutrition for their hosts. The most commonly observed parasites belong to marine alveolates Syndiniales, such as Merodinium, Solenodinium, and Syndinium (Anderson, 1983; Coats, 1999; Dolven et al, 2007)
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