N-Linked Surface Glycan Biosynthesis, Composition, Inhibition, and Function in Cnidarian-Dinoflagellate Symbiosis

Abstract

The success of symbioses between cnidarian hosts (e.g. corals and sea anemones) and microalgal symbionts hinges on the molecular interactions that govern the establishment and maintenance of intracellular mutualisms. As a fundamental component of innate immunity, glycan-lectin interactions impact the onset of marine endosymbioses, but our understanding of the effects of cell surface glycome composition on symbiosis establishment remains limited. In this study, we examined the canonical N-glycan biosynthesis pathway in the genome of the dinoflagellate symbiont Breviolum minutum (family Symbiodiniaceae) and found it to be conserved with the exception of the transferase GlcNAc-TII (MGAT2). Using coupled liquid chromatography-mass spectrometry (LC-MS/MS), we characterized the cell surface N-glycan content of B. minutum, providing the first insight into the molecular composition of surface glycans in dinoflagellates. We then used the biosynthesis inhibitors kifunensine and swainsonine to alter the glycan composition of B. minutum. Successful high-mannose enrichment via kifunensine treatment resulted in a significant decrease in colonization of the model sea anemone Aiptasia (Exaiptasia pallida) by B. minutum. Hybrid glycan enrichment via swainsonine treatment, however, could not be confirmed and did not impact colonization. We conclude that functional Golgi processing of N-glycans is critical for maintaining appropriate cell surface glycan composition and for ensuring colonization success by B. minutum.

Symbiosis maintenance in the facultative coral, Oculina arbuscula, relies on nitrogen cycling, cell cycle modulation, and immunity

“… 29 – 32 ). Work in these systems has uncovered key mechanisms for control of symbiont densities 33 – 35 , lectin and other proteins involved in symbiont recognition and endocytosis 36 , 37 , as well as differences in the repression of the host immune system by symbionts of different genera 38 . Still, much can be learned from studying adult calcifying corals in a naturally aposymbiotic state.…”

Heat Stress of Algal Partner Hinders Colonization Success and Alters the Algal Cell Surface Glycome in a Cnidarian-Algal Symbiosis

“…Several specific glycan moieties have been characterized in Symbiodiniaceae. High-mannoside glycans are the most abundant type of N-glycan in B. minutum , but increasing the abundance of high-mannoside glycans with inhibitors for glycan maturation pathways can decrease the colonization capacity of B. minutum ( 12 ). Similarly, Tortorelli et al ( 13 ) found higher abundances of high-mannoside glycans as measured by lectin array in nonnative species of algae, Cladocopium goreaui , and Fugacium kawagutii , compared to B. minutum , suggesting that an overabundance of high-mannoside glycans can inhibit symbiosis.…”

“…Similarly, Tortorelli et al ( 13 ) found higher abundances of high-mannoside glycans as measured by lectin array in nonnative species of algae, Cladocopium goreaui , and Fugacium kawagutii , compared to B. minutum , suggesting that an overabundance of high-mannoside glycans can inhibit symbiosis. The second-most abundant group of N-glycans in B. minutum are galactosylated glycans ( 12 ). These glycans are less abundant in nonnative species of algae, Symbiodinium pilosum , C. goreaui , and F. kawagutii , as measured by lectin array compared to B. minutum ( 11 , 13 ).…”

“…This supports the hypothesis that galactosylation is a marker for a compatible symbiont in Aiptasia ( 11 , 13 ). Sialylated glycans have also been detected in Symbiodiniaceae in several recent studies, but their role in symbiosis remains unclear, and their abundance is low ( 11 – 13 ). While sialylation has numerous biological roles in the deuterostomes, its presence in other eukaryotic lineages has only recently been acknowledged ( 25 – 27 ).…”

“…While sialylation has numerous biological roles in the deuterostomes, its presence in other eukaryotic lineages has only recently been acknowledged ( 25 – 27 ). Crucially, genes involved in sialylation have been found in Symbiodiniaceae and cnidarians, including scleractinian corals and Aiptasia, suggesting that sialylated glycans play a role in symbiotic interactions ( 12 , 28 ).…”