Evidence for a role of protein phosphorylation in the maintenance of the cnidarian–algal symbiosis

Abstract

The endosymbiotic relationship between cnidarians and photosynthetic dinoflagellate algae provides the foundation of coral reef ecosystems. This essential interaction is globally threatened by anthropogenic disturbance. As such, it is important to understand the molecular mechanisms underpinning the cnidarian–algal association. Here we investigated phosphorylation‐mediated protein signalling as a mechanism of regulation of the cnidarian–algal interaction, and we report on the generation of the first phosphoproteome for the coral model system Aiptasia. Mass spectrometry‐based phosphoproteomics using data‐independent acquisition allowed consistent quantification of over 3,000 phosphopeptides totalling more than 1,600 phosphoproteins across aposymbiotic (symbiont‐free) and symbiotic anemones. Comparison of the symbiotic states showed distinct phosphoproteomic profiles attributable to the differential phosphorylation of 539 proteins that cover a broad range of functions, from receptors to structural and signal transduction proteins. A subsequent pathway enrichment analysis identified the processes of “protein digestion and absorption,” “carbohydrate metabolism,” and “protein folding, sorting and degradation,” and highlighted differential phosphorylation of the “phospholipase D signalling pathway” and “protein processing in the endoplasmic reticulum.” Targeted phosphorylation of the phospholipase D signalling pathway suggests control of glutamate vesicle trafficking across symbiotic compartments, and phosphorylation of the endoplasmic reticulum machinery suggests recycling of symbiosome‐associated proteins. Our study shows for the first time that changes in the phosphorylation status of proteins between aposymbiotic and symbiotic Aiptasia anemones may play a role in the regulation of the cnidarian–algal symbiosis. This is the first phosphoproteomic study of a cnidarian–algal symbiotic association as well as the first application of quantification by data‐independent acquisition in the coral field.

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

“…Consistent with previous work (e.g. 68 , 69 ), several genes involved in glutamate synthesis pathways, including glutamate and glutamine synthetases and glutamate dehydrogenases were all significantly upregulated in symbiotic branches (Fig. 3 A).…”

Surface Topography, Bacterial Carrying Capacity, and the Prospect of Microbiome Manipulation in the Sea Anemone Coral Model Aiptasia

“…Symbiotic anemones were generated by infecting aposymbiotic animals with strain SSB01 (Breviolum minutum, former Clade B) (Xiang et al, 2013). Of note, the algal symbiont strain SSB01 is not the native symbiont of Aiptasia CC7 but has been previously used as a stable and characterized Aiptasia host-algal symbiont combination (Röthig et al, 2016a;Wolfowicz et al, 2016;Simona et al, 2019). To obtain symbiotic CC7-SSB01 Aiptasia, individual anemones were exposed to 10 5 Symbiodiniaceae cells/ml for 24 h, fed with Artemia nauplii after 48 h, and seawater was exchanged thereafter.…”

“…Therefore, they may not comprise an ideal model for corals, since association with Symbiodiniaceae affects bacterial assemblage (Ainsworth et al, 2015;Röthig et al, 2016a;Lawson et al, 2018;Maire et al, 2021). To this end, the sea anemone Aiptasia is gaining increasing traction as a coral model due to harboring the same or similar Symbiodiniaceae as scleractinian corals, its simplicity of culturing and clonal propagation, and the fact that Aiptasia anemones can be kept indefinitely in symbiotic and aposymbiotic states (i.e., with and without their microalgal partners) (Weis et al, 2008;Voolstra, 2013), allowing to study the mechanistic underpinnings of the cnidarian-dinoflagellate symbiosis in detail (Baumgarten et al, 2015;Biquand et al, 2017;Cziesielski et al, 2018;Rädecker et al, 2018;Gegner et al, 2019;Simona et al, 2019). Of note, the name Aiptasia refers to the colloquial model system name, given that different researchers across the world use different strains, and likely species (Weis et al, 2008;Baumgarten et al, 2015;Oakley et al, 2015;Biquand et al, 2017;Dungan et al, 2020).…”

Broad scale proteomic analysis of heat-destabilised symbiosis in the hard coral Acropora millepora

“…Recent analytical advancements and the broader uptake of ‘omics approaches have accelerated our understanding of the metabolic maintenance and regulation of this important partnership. Transcriptomic 25 – 27 and proteomic 28 – 30 studies comparing symbiotic and aposymbiotic Aiptasia have uncovered symbiosis-specific genes, proteins and metabolic pathways, highlighting nutrient exchange and transport processes 26 , 28 , 30 , as well as protein phosphorylation status 31 , as notable indicators of symbiotic state. Investigations into the cellular response of the cnidarian host ( Aiptasia or coral) and/or its dinoflagellate symbiont to thermal stress have also been targeted with transcriptomic 22 , 32 , proteomic 29 , 33 , 34 and metabolomic 35 – 37 analyses.…”