Supplementation of exogenous lipids via liposomes improves coral larvae settlement post-cryopreservation and nano-laser warming.

Coral reefs worldwide are receding because of detrimental human activities, and cryopreservation of coral larvae would ensure that their genetic biodiversity is not irremediably lost. In recent years, the vitrification and laser warming of coral propagules has demonstrated promising results. During cryopreservation, cellular membranes undergo substantial reconfigurations that may affect survival. Fat enrichment may alter the physical proprieties of cell membranes and improve resistance to low temperatures. Therefore, the aim of this study was to determine whether supplementation of exogenous lipids using liposomes would improve cryosurvival and further development of the vitrified and laser-warmed coral larvae of Seriatopora caliendrum and Pocillopora verrucosa. A vitrification solution (VS) composed of 2 M ethylene glycol (EG), 1 M propylene glycol (PG), 40% (w/v) Ficoll, and 10% gold nanoparticles (at a final concentration of 1.2 × 1018 particles/m3 and an optimised emission wavelength of 535 nm) was chosen. Coral larvae were subjected to vitrification with VS incorporating one of four lipid classes: phosphatidylcholine (PC), phosphatidylethanolamine (PE), erucic acid (EA), and linoleic acid (LA). Warming was achieved using a single laser pulse (300 V, 10 ms pulse width, 2 mm laser beam diameter). A significantly higher vitality rate was observed in S. caliendrum larvae subjected to vitrification and laser warming with EA-incorporated VS, and P. verrucosa larvae vitrified and laser warmed using PE-incorporated VS achieved a significantly higher settlement rate. Our study demonstrated that supplementation of exogenous lipids with liposomes enhances coral larvae cryotolerance and improves cryopreservation outcomes. Lipid enrichment may play a key role in cryobanking coral propagules, and in propagule development after thawing.

Lipid consumption in coral larvae differs among sites: a consideration of environmental history in a global ocean change scenario.

The success of early life-history stages is an environmentally sensitive bottleneck for many marine invertebrates. Responses of larvae to environmental stress may vary due to differences in maternal investment of energy stores and acclimatization/adaptation of a population to local environmental conditions. In this study, we compared two populations from sites with different environmental regimes (Moorea and Taiwan). We assessed the responses of Pocillopora damicornis larvae to two future co-occurring environmental stressors: elevated temperature and ocean acidification. Larvae from Taiwan were more sensitive to temperature, producing fewer energy-storage lipids under high temperature. In general, planulae in Moorea and Taiwan responded similarly to pCO2 Additionally, corals in the study sites with different environments produced larvae with different initial traits, which may have shaped the different physiological responses observed. Notably, under ambient conditions, planulae in Taiwan increased their stores of wax ester and triacylglycerol in general over the first 24 h of their dispersal, whereas planulae from Moorea consumed energy-storage lipids in all cases. Comparisons of physiological responses of P. damicornis larvae to conditions of ocean acidification and warming between sites across the species' biogeographic range illuminates the variety of physiological responses maintained within P. damicornis, which may enhance the overall persistence of this species in the light of global climate change.

Dual-compartmental transcriptomic + proteomic analysis of a marine endosymbiosis exposed to environmental change.

As significant anthropogenic pressures are putting undue stress on the world's oceans, there has been a concerted effort to understand how marine organisms respond to environmental change. Transcriptomic approaches, in particular, have been readily employed to document the mRNA-level response of a plethora of marine invertebrates exposed to an array of simulated stress scenarios, with the tacit and untested assumption being that the respective proteins show a corresponding trend. To better understand the degree of congruency between mRNA and protein expression in an endosymbiotic marine invertebrate, mRNAs and proteins were sequenced from the same samples of the common, Indo-Pacific coral Seriatopora hystrix exposed to stable or upwelling-simulating conditions for 1 week. Of the 167 proteins downregulated at variable temperature, only two were associated with mRNAs that were also differentially expressed between treatments. Of the 378 differentially expressed genes, none were associated with a differentially expressed protein. Collectively, these results highlight the inherent risk of inferring cellular behaviour based on mRNA expression data alone and challenge the current, mRNA-focused approach taken by most marine and many molecular biologists.

Different strategies of energy storage in cultured and freshly isolated Symbiodinium sp.

The endosymbiotic relationship between cnidarians and Symbiodinium is critical for the survival of coral reefs. In this study, we developed a protocol to rapidly and freshly separate Symbiodinium from corals and sea anemones. Furthermore, we compared these freshly-isolated Symbiodinium with cultured Symbiodinium to investigate host and Symbiodinium interaction. Clade B Symbiodinium had higher starch content and lower lipid content than those of clades C and D in both freshly isolated and cultured forms. Clade C had the highest lipid content, particularly when associated with corals. Moreover, the coral-associated Symbiodinium had higher protein content than did cultured and sea anemone-associated Symbiodinium. Regarding fatty acid composition, cultured Symbiodinium and clades B, C, and D shared similar patterns, whereas sea anemone-associated Symbiodinium had a distinct pattern compared coral-associated Symbiodinium. Specifically, the levels of monounsaturated fatty acids were lower than those of the saturated fatty acids, and the level of polyunsaturated fatty acids (PUFAs) were the highest in all examined Symbiodinium. Furthermore, PUFAs levels were higher in coral-associated Symbiodinium than in cultured Symbiodinium. These results altogether indicated that different Symbiodinium clades used different energy storage strategies, which might be modified by hosts.

Compartment-specific transcriptomics in a reef-building coral exposed to elevated temperatures.

Although rising ocean temperatures threaten scleractinian corals and the reefs they construct, certain reef corals can acclimate to elevated temperatures to which they are rarely exposed in situ. Specimens of the model Indo-Pacific reef coral Pocillopora damicornis collected from upwelling reefs of Southern Taiwan were previously found to have survived a 36-week exposure to 30°C, a temperature they encounter infrequently and one that can elicit the breakdown of the coral-dinoflagellate (genus Symbiodinium) endosymbiosis in many corals of the Pacific Ocean. To gain insight into the subcellular pathways utilized by both the coral hosts and their mutualistic Symbiodinium populations to acclimate to this temperature, mRNAs from both control (27°C) and high (30°C)-temperature samples were sequenced on an Illumina platform and assembled into a 236 435-contig transcriptome. These P. damicornis specimens were found to be ~60% anthozoan and 40% microbe (Symbiodinium, other eukaryotic microbes, and bacteria), from an mRNA-perspective. Furthermore, a significantly higher proportion of genes from the Symbiodinium compartment were differentially expressed after two weeks of exposure. Specifically, at elevated temperatures, Symbiodinium populations residing within the coral gastrodermal tissues were more likely to up-regulate the expression of genes encoding proteins involved in metabolism than their coral hosts. Collectively, these transcriptome-scale data suggest that the two members of this endosymbiosis have distinct strategies for acclimating to elevated temperatures that are expected to characterize many of Earth's coral reefs in the coming decades.

Nutrient limitation in Auxenochlorella protothecoides induces qualitative changes of fatty acid and expression of caleosin as a membrane protein associated with oil bodies.

Oil bodies formed in Auxenochlorella protothecoides induced during limited nutrition had a coating of caleosin. The total lipid content obtained from A. protothecoides in unstressed cultures (first week) was ~210 mg/g compared to the 231 mg/g obtained in the third week (nutrient limited) and 290 mg/g obtained in the fourth week (nutrient limited). The proportion of total saturated fatty acids increased from 28 to 46 %, whereas that of total polyunsaturated fatty acids decreased from 52 to 35 %. The expression levels of the 28 kDa caleosin protein in A. protothecoides rose to a maximum up to 4 weeks; immunolocalization studies showed that caleosin was predominantly associated with the membranes of oil bodies.

The effects of a variable temperature regime on the physiology of the reef-building coral Seriatopora hystrix: results from a laboratory-based reciprocal transplant.

To understand the effects of global climate change on reef-building corals, a thorough investigation of their physiological mechanisms of acclimatization is warranted. However, static temperature manipulations may underestimate the thermal complexity of the reefs in which many corals live. For instance, corals of Houbihu, Taiwan, experience changes in temperature of up to 10°C over the course of a day during spring-tide upwelling events. To better understand the phenotypic plasticity of these corals, a laboratory-based experiment was conducted whereby specimens of Seriatopora hystrix from an upwelling reef (Houbihu) and conspecifics from a non-upwelling reef (Houwan) were exposed to both a stable seawater temperature (26°C) regime and a regime characterized by a 6°C fluctuation (23-29°C) over a 12 h period for 7 days. A suite of physiological and molecular parameters was measured in samples of both treatments, as well as in experimental controls, to determine site of origin (SO) and temperature treatment (TT) responses. Only chlorophyll a (chl a) concentration and growth demonstrated the hypothesized trend of higher levels when exposed to a TT that mimicked SO conditions. In contrast, chl a, maximum dark-adapted quantum yield of photosystem II (F(v)/F(m)), and Symbiodinium ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL), photosystem I (psI, subunit III) and phosphoglycolate phosphatase (pgpase) mRNA expression demonstrated significant TT effects. Specifically, levels of these response variables were higher in samples exposed to a variable temperature regime, suggesting that S. hystrix may acclimate to fluctuating temperatures by increasing its capacity for photosynthesis.

Assessment of metabolic modulation in free-living versus endosymbiotic Symbiodinium using synchrotron radiation-based infrared microspectroscopy.

The endosymbiotic relationship between coral hosts and dinoflagellates of the genus Symbiodinium is critical for the growth and productivity of coral reef ecosystems. Here, synchrotron radiation-based infrared microspectroscopy was applied to examine metabolite concentration differences between endosymbiotic (within the anemone Aiptasia pulchella) and free-living Symbiodinium over the light-dark cycle. Significant differences in levels of lipids, nitrogenous compounds, polysaccharides and putative cell wall components were documented. Compared with free-living Symbiodinium, total lipids, unsaturated lipids and polysaccharides were relatively enriched in endosymbiotic Symbiodinium during both light and dark photoperiods. Concentrations of cell wall-related metabolites did not vary temporally in endosymbiotic samples; in contrast, the concentrations of these metabolites increased dramatically during the dark photoperiod in free-living samples, possibly reflecting rhythmic cell-wall synthesis related to light-driven cell proliferation. The level of nitrogenous compounds in endosymbiotic cells did not vary greatly across the light-dark cycle and in general was significantly lower than that observed in free-living samples collected during the light. Collectively, these data suggest that nitrogen limitation is a factor that the host cell exploits to induce the biosynthesis of lipids and polysaccharides in endosymbiotic Symbiodinium.

Lipid bodies in coral-dinoflagellate endosymbiosis: proteomic and ultrastructural studies.

Gastrodermal lipid bodies (LBs) are organelles involved in the regulation of the mutualistic endosymbiosis between reef-building corals and their dinoflagellate endosymbionts (genus Symbiodinium). As their molecular composition remains poorly defined, we herein describe the first gastrodermal LB proteome and examine in situ morphology of LBs in order to provide insight into their structure and function. After tissue separation of the tentacles of the stony coral Euphyllia glabrescens, buoyant LBs of the gastroderm encompassing a variety of sizes (0.5-4 µm in diameter) were isolated after two cycles of subcellular fractionation via stepwise sucrose gradient ultracentrifugation and detergent washing. The purity of the isolated LBs was demonstrated by their high degree of lipid enrichment and as well as the absence of contaminating proteins of the host cell and Symbiodinium. LB-associated proteins were then purified, subjected to SDS-PAGE, and identified by MS using an LC-nano-ESI-MS/MS. A total of 42 proteins were identified within eight functional groups, including metabolism, intracellular trafficking, the stress response/molecular modification and development. Ultrastructural analyses of LBs in situ showed that they exhibit defined morphological characteristics, including a high-electron density resulting from a distinct lipid composition from that of the lipid droplets of mammalian cells. Coral LBs were also characterized by the presence of numerous electron-transparent inclusions of unknown origin and composition. Both proteomic and ultrastructural observations seem to suggest that both Symbiodinium and host organelles, such as the ER, are involved in LB biogenesis.

The characteristics of host lipid body biogenesis during coral-dinoflagellate endosymbiosis.

Intracellular lipid body (LB) biogenesis depends on the symbiosis between coral hosts and their Symbiodinaceae. Therefore, understanding the mechanism(s) behind LB biosynthesis in corals can portentially elucide the drivers of cellular regulation during endosymbiosis. This study assessed LB formation in the gastrodermal tissue layer of the hermatypic coral Euphyllia glabrescens. Diel rhythmicity in LB size and distribution was observed; solar irradiation onset at sunrise initiated an increase in LB formation, which continued throughout the day and peaked after sunset at 18:00. The LBs migrated from the area near the mesoglea to the gastrodermal cell border near the coelenteron. Micro-LB biogenesis occurred in the endoplasmic reticulum (ER) of the host gastrodermal cells. A transcriptomic analysis of genes related to lipogenesis indicated that binding immunoglobulin protein (BiP) plays a key role in metabolic signaling pathways. The diel rhythmicity of LB biogenesis was correlated with ER-localized BiP expression. BiP expression peaked during the period with the largest increase in LB formation, thereby indicating that the chaperoning reaction of abnormal protein folding inside the host ER is likely involved in LB biosynthesis. These findings suggest that the host ER, central to LB formation, potentially facilitates the regulation of endosymbiosis between coral hosts and Symbiodiniaceae.

Proteomic analysis of symbiosome membranes in Cnidaria-dinoflagellate endosymbiosis.

Symbiosomes are specific intracellular membrane-bound vacuoles containing microalgae in a mutualistic Cnidaria (host)-dinoflagellate (symbiont) association. The symbiosome membrane is originally derived from host plasma membranes during phagocytosis of the symbiont; however, its molecular components and functions are not clear. In order to investigate the protein components of the symbiosome membranes, homogenous symbiosomes were isolated from the sea anemone Aiptasia pulchella and their purities and membrane intactness examined by Western blot analysis for host contaminants and microscopic analysis using various fluorescent probes, respectively. Pure and intact symbiosomes were then subjected to biotinylation by a cell impermeant agent (Biotin-XX sulfosuccinimidyl ester) to label membrane surface proteins. The biotinylated proteins, both Triton X-100 soluble and insoluble fractions, were subjected to 2-D SDS-PAGE and identified by MS using an LC-nano-ESI-MS/MS. A total of 17 proteins were identified. Based on their different subcellular origins and functional categories, it indicates that symbiosome membranes serve as the interface for interaction between host and symbiont by fulfilling several crucial cellular functions such as those of membrane receptors/cell recognition, cytoskeletal remodeling, ATP synthesis/proton homeostasis, transporters, stress responses/chaperones, and anti-apoptosis. The results of proteomic analysis not only indicate the molecular identity of the symbiosome membrane, but also provide insight into the possible role of symbiosome membranes during the endosymbiotic association.

A shift away from mutualism under food-deprived conditions in an anemone-dinoflagellate association.

The mutualistic symbiosis between anthozoans and intra-gastrodermal dinoflagellates of the family Symbiodiniaceae is the functional basis of all coral reef ecosystems, with the latter providing up to 95% of their fixed photosynthate to their hosts in exchange for nutrients. However, recent studies of sponges, jellyfish, and anemones have revealed the potential for this mutualistic relationship to shift to parasitism under stressful conditions. Over a period of eight weeks, we compared the physiological conditions of both inoculated and aposymbiotic anemones (Exaiptasia pallida) that were either fed or starved. By the sixth week, both fed groups of anemones were significantly larger than their starved counterparts. Moreover, inoculated and starved anemones tended to disintegrate into "tissue balls" within eight weeks, and 25% of the samples died; in contrast, starved aposymbiotic anemones required six months to form tissue balls, and no anemones from this group died. Our results show that the dinoflagellates within inoculated anemones may have posed a fatal metabolic burden on their hosts during starvation; this may be because of the need to prioritize their own metabolism and nourishment at the expense of their hosts. Collectively, our study reveals the potential of this dynamic symbiotic association to shift away from mutualism during food-deprived conditions.

First instance of settlement by cryopreserved coral larvae in symbiotic association with dinoflagellates.

Coral reefs are suffering on a global scale due to human impacts, thereby necessitating cryopreservation efforts. The objective of this study was to develop a suitable vitrification and laser warming protocol for larvae of the scleractinian coral Seriatopora caliendrum, which inherit their dinoflagellate algal symbionts vertically. Toxicity experiments were conducted with the cryoprotectants (CPAs) ethylene glycol (EG), propylene glycol (PG), dimethyl sulfoxide (DMSO), glycerol (GLY), and methanol (METH; listed in order from least to most toxic), and larvae were subjected to vitrification and laser warming using 2 M EG + 1 M PG and 2 M EG + 1 M DMSO. Vitrification and laser warming (300 V, 10 ms pulse width, 2 mm beam diameter) using a vitrification solution of 2 M EG + 1 M PG, 40% w/v Ficoll, and 10% v/v gold nanobars (GNB) at a final concentration of 1.2 × 1018 GNB/mL and a characteristic wavelength of 535 nm resulted in larvae with vitality and settlement percentages of 55 and 9%, respectively. This represents the first successful instance of cryopreservation of coral larvae that proceeded to settle upon warming, and suggests that the vitrification and ultra-fast laser warming approach may be applicable to other threatened marine species.

The proteomic response of the reef coral Pocillopora acuta to experimentally elevated temperatures.

Although most reef-building corals live near the upper threshold of their thermotolerance, some scleractinians are resilient to temperature increases. For instance, Pocillopora acuta specimens from an upwelling habitat in Southern Taiwan survived a nine-month experimental exposure to 30°C, a temperature hypothesized to induce stress. To gain a greater understanding of the molecular pathways underlying such high-temperature acclimation, the protein profiles of experimental controls incubated at 27°C were compared to those of conspecific P. acuta specimens exposed to 30°C for two, four, or eight weeks, and differentially concentrated proteins (DCPs) were removed from the gels and sequenced with mass spectrometry. Sixty unique DCPs were uncovered across both eukaryotic compartments of the P. acuta-dinoflagellate (genus Symbiodinium) mutualism, and Symbiodinium were more responsive to high temperature at the protein-level than the coral hosts in which they resided at the two-week sampling time. Furthermore, proteins involved in the stress response were more likely to be documented at different cellular concentrations across temperature treatments in Symbiodinium, whereas the temperature-sensitive host coral proteome featured numerous proteins involved in cytoskeletal structure, immunity, and metabolism. These proteome-scale data suggest that the coral host and its intracellular dinoflagellates have differing strategies for acclimating to elevated temperatures.

Setting the pace: host rhythmic behaviour and gene expression patterns in the facultatively symbiotic cnidarian Aiptasia are determined largely by Symbiodinium.

BACKGROUND: All organisms employ biological clocks to anticipate physical changes in the environment; however, the integration of biological clocks in symbiotic systems has received limited attention. In corals, the interpretation of rhythmic behaviours is complicated by the daily oscillations in tissue oxygen tension resulting from the photosynthetic and respiratory activities of the associated algal endosymbiont Symbiodinium. In order to better understand the integration of biological clocks in cnidarian hosts of Symbiodinium, daily rhythms of behaviour and gene expression were studied in symbiotic and aposymbiotic morphs of the sea-anemone Aiptasia diaphana. RESULTS: The results showed that whereas circatidal (approx. 12-h) cycles of activity and gene expression predominated in aposymbiotic morphs, circadian (approx. 24-h) patterns were the more common in symbiotic morphs, where the expression of a significant number of genes shifted from a 12- to 24-h rhythm. The behavioural experiments on symbiotic A. diaphana displayed diel (24-h) rhythmicity in body and tentacle contraction under the light/dark cycles, whereas aposymbiotic morphs showed approximately 12-h (circatidal) rhythmicity. Reinfection experiments represent an important step in understanding the hierarchy of endogenous clocks in symbiotic associations, where the aposymbiotic Aiptasia morphs returned to a 24-h behavioural rhythm after repopulation with algae. CONCLUSION: Whilst some modification of host metabolism is to be expected, the extent to which the presence of the algae modified host endogenous behavioural and transcriptional rhythms implies that it is the symbionts that influence the pace. Our results clearly demonstrate the importance of the endosymbiotic algae in determining the timing and the duration of the extension and contraction of the body and tentacles and temporal gene expression.

Identifying corals displaying aberrant behavior in Fiji's Lau Archipelago.

Given the numerous threats against Earth's coral reefs, there is an urgent need to develop means of assessing reef coral health on a proactive timescale. Molecular biomarkers may prove useful in this endeavor because their expression should theoretically undergo changes prior to visible signs of health decline, such as the breakdown of the coral-dinoflagellate (genus Symbiodinium) endosymbiosis. Herein 13 molecular- and physiological-scale biomarkers spanning both eukaryotic compartments of the anthozoan-Symbiodinium mutualism were assessed across 70 pocilloporid coral colonies sampled from reefs of Fiji's easternmost province, Lau. Eleven colonies were identified as outliers upon employment of a detection method based partially on the Mahalanobis distance; these corals were hypothesized to have been displaying aberrant sub-cellular behavior with respect to their gene expression signatures, as they were characterized not only by lower Symbiodinium densities, but also by higher levels of expression of several stress-targeted genes. Although these findings could suggest that the sampled colonies were physiologically compromised at the time of sampling, further studies are warranted to state conclusively whether these 11 scleractinian coral colonies are more stress-prone than nearby conspecifics that demonstrated statistically normal phenotypes.

Biomarker profiling in reef corals of Tonga's Ha'apai and Vava'u archipelagos.

Given the significant threats towards Earth's coral reefs, there is an urgent need to document the current physiological condition of the resident organisms, particularly the reef-building scleractinians themselves. Unfortunately, most of the planet's reefs are understudied, and some have yet to be seen. For instance, the Kingdom of Tonga possesses an extensive reef system, with thousands of hectares of unobserved reefs; little is known about their ecology, nor is there any information on the health of the resident corals. Given such knowledge deficiencies, 59 reefs across three Tongan archipelagos were surveyed herein, and pocilloporid corals were sampled from approximately half of these surveyed sites; 10 molecular-scale response variable were assessed in 88 of the sampled colonies, and 12 colonies were found to be outliers based on employment of a multivariate statistics-based aberrancy detection system. These outliers differed from the statistically normally behaving colonies in having not only higher RNA/DNA ratios but also elevated expression levels of three genes: 1) Symbiodinium zinc-induced facilitator-like 1-like, 2) host coral copper-zinc superoxide dismutase, and 3) host green fluorescent protein-like chromoprotein. Outliers were also characterized by significantly higher variation amongst the molecular response variables assessed, and the response variables that contributed most significantly to colonies being delineated as outliers differed between the two predominant reef coral species sampled, Pocillopora damicornis and P. acuta. These closely related species also displayed dissimilar temporal fluctuation patterns in their molecular physiologies, an observation that may have been driven by differences in their feeding strategies. Future works should attempt to determine whether corals displaying statistically aberrant molecular physiology, such as the 12 Tongan outliers identified herein, are indeed characterized by a diminished capacity for acclimating to the rapid changes in their abiotic milieu occurring as a result of global climate change.

Identification of caleosin and oleosin in oil bodies of pine pollen.

Unique proteins including steroleosin, caleosin, oleosin-L, and oleosin-G have been identified in seed oil bodies of pine (Pinus massoniana). In this study, mature pollen grains with wing-like bladders were collected from pine (Pinus elliottii). Ultrastructural studies showed that oil bodies were present in pollen grains, but not the attached bladders, and the presence of oil bodies was further confirmed by fluorescent staining with BODIPY 493/503. Stable oil bodies were successfully purified from pine pollen grains, and analyzed to be mainly composed of triacylglycerols. Putative oleosin and caleosin in pine pollen oil bodies were detected by immunoassaying with antibodies against sesame seed caleosin and lily pollen oleosin. Complete cDNA fragments encoding these two pollen oil-body proteins were obtained by PCR cloning. Sequence alignment showed that pine pollen caleosin (27 kDa) was highly homologous to pine seed caleosin (28 kDa) except for the lack of an appendix of eight residues at the C-terminus in accord with the 1 kDa difference in their molecular masses. Pine pollen oleosin (15 kDa) was highly homologous to pine seed oleosin-G (14 kDa) except for an insertion of eight residues at the N-terminus in accord with the 1 kDa difference in their molecular masses.

A detailed observation of the ejection and retraction of defense tissue acontia in sea anemone (Exaiptasia pallida).

Acontia, located in the gastrovascular cavity of anemone, are thread-like tissue containing numerous stinging cells which serve as a unique defense tissue against predators of the immobile acontiarian sea anemone. Although its morphology and biological functions, such as defense and digestion, have been studied, the defense behavior and the specific events of acontia ejection and retraction are unclear. The aim of this study is to observe and record the detailed process of acontia control in anemones. Observations reveal that the anemone, Exaiptasia pallida, possibly controls a network of body muscles and manipulates water pressure in the gastrovascular cavity to eject and retract acontia. Instead of resynthesizing acontia after each ejection, the retraction and reuse of acontia enables the anemone to respond quickly at any given time, thus increasing its overall survivability. Since the Exaiptasia anemone is an emerging model for coral biology, this study provides a foundation to further investigate the biophysics, neuroscience, and defense biology of this marine model organism.

Coral lipid bodies as the relay center interconnecting diel-dependent lipidomic changes in different cellular compartments.

Lipid bodies (LBs) in the coral gastrodermal tissues are key organelles in the regulation of endosymbiosis and exhibit a diel rhythmicity. Using the scleractinian Euphyllia glabrescens collected across the diel cycle, we observed temporally dynamic lipid profiles in three cellular compartments: host coral gastrodermal cells, LBs, and in hospite Symbiodinium. Particularly, the lipidome varied over time, demonstrating the temporally variable nature of the coral-Symbiodinium endosymbiosis. The lipidome-scale data highlight the dynamic, light-driven metabolism of such associations and reveal that LBs are not only lipid storage organelles but also act as a relay center in metabolic trafficking. Furthermore, lipogenesis in LBs is significantly regulated by coral hosts and the lipid metabolites within holobionts featured predominantly triacylglycerols, sterol esters, and free fatty acids. Given these findings through a time-varied lipidome status, the present study provided valuable insights likely to be crucial to understand the cellular biology of the coral-Symbiodinium endosymbiosis.