Transcriptional characterisation of the Aiptasia pallida pedal disc

Background Biological adhesion (bioadhesion), enables organisms to attach to surfaces as well as to a range of other targets. Bioadhesion evolved numerous times independently and is ubiquitous throughout the kingdoms of life. To date, investigations have focussed on various taxa of animals, plants and bacteria, but the fundamental processes underlying bioadhesion and the degree of conservation in different biological systems remain poorly understood. This study had two aims: 1) To characterise tissue-specific gene regulation in the pedal disc of a basal metazoan; the model cnidarian Aiptasia pallida, and 2) to elucidate the specific genes involved in pedal disc adhesion. Results Five hundred and forty-seven genes were differentially expressed in the pedal disc compared to the rest of the animal. Four hundred and twenty-seven genes were significantly upregulated and one hundred and twenty genes were significantly downregulated. Forty-one condensed gene ontology terms and 19 protein superfamily classifications were enriched in the pedal disc. Eight condensed gene ontology terms and 11 protein superfamily classifications were depleted. Enriched superfamilies were consistent with classifications identified previously as important for the bioadhesion of unrelated marine invertebrates. A host of genes involved in regulation of extra cellular matrix generation and degradation were identified, as well as others related to development and immunity. Ab initio prediction identified 173 upregulated genes that putatively code for extracellularly secreted proteins. Conclusion The analytical workflow facilitated identification of genes involved in adhesion, immunity, defence and development of the A. pallida pedal disc. When defence, immunity and development-related genes were identified, those remaining corresponded most closely to formation of the extracellular matrix (ECM), implicating ECM in the adhesion of anemones to surfaces. This study therefore provides a valuable high-throughput resource for the bioadhesion community and lays a foundation for further targeted research to elucidate bioadhesion in the Cnidaria.

Reduced representation sequencing for symbiotic anthozoans: are reference genomes necessary to eliminate endosymbiont contamination and make robust phylogeographic inference?

Anthozoan cnidarians form the backbone of coral reefs. Their success relies on endosymbiosis with photosynthetic dinoflagellates in the family Symbiodiniaceae. Photosymbionts represent a hurdle for researchers using population genomic techniques to study these highly imperiled and ecologically critical species because sequencing datasets harbor unknown mixtures of anthozoan and photosymbiont loci. Here we use range-wide sampling and a double-digest restriction-site associated DNA sequencing (ddRADseq) of the sea anemone Bartholomea annulata to explore how symbiont loci impact the interpretation of phylogeographic patterns and population genetic parameters. We use the genome of the closely related Exaiptasia diaphana (previously Aiptasia pallida) to create an anthozoan-only dataset from a genomic dataset containing both B. annulata and its symbiodiniacean symbionts and then compare this to the raw, holobiont dataset. For each, we investigate spatial patterns of genetic diversity and use coalescent model-based approaches to estimate demographic history and population parameters. The Florida Straits are the only phylogeographic break we recover for B. annulata, with divergence estimated during the last glacial maximum. Because B. annulata hosts multiple members of Symbiodiniaceae, we hypothesize that, under moderate missing data thresholds, de novo clustering algorithms that identify orthologs across datasets will have difficulty identifying shared non-coding loci from the photosymbionts. We infer that, for anthozoans hosting diverse members of Symbiodinaceae, clustering algorithms act as de facto filters of symbiont loci. Thus, while at least some photosymbiont loci remain, these are swamped by orders of magnitude greater numbers of anthozoan loci and thus represent genetic “noise,” rather than contributing genetic signal.

Multi-omics analysis of thermal stress response in a zooxanthellate cnidarian reveals the importance of associating with thermotolerant symbionts

Corals and their endosymbiotic dinoflagellates of the genus Symbiodinium have a fragile relationship that breaks down under heat stress, an event known as bleaching. However, many coral species have adapted to high temperature environments such as the Red Sea (RS). To investigate mechanisms underlying temperature adaptation in zooxanthellate cnidarians we compared transcriptome- and proteome-wide heat stress response (24 h at 32°C) of three strains of the model organism Aiptasia pallida from regions with differing temperature profiles; North Carolina (CC7), Hawaii (H2) and the RS. Correlations between transcript and protein levels were generally low but inter-strain comparisons highlighted a common core cnidarian response to heat stress, including protein folding and oxidative stress pathways. RS anemones showed the strongest increase in antioxidant gene expression and exhibited significantly lower reactive oxygen species (ROS) levels in hospite . However, comparisons of antioxidant gene and protein expression between strains did not show strong differences, indicating similar antioxidant capacity across the strains. Subsequent analysis of ROS production in isolated symbionts confirmed that the observed differences of ROS levels in hospite were symbiont-driven. Our findings indicate that RS anemones do not show increased antioxidant capacity but may have adapted to higher temperatures through association with more thermally tolerant symbionts.

Mitigation of coral bleaching by antioxidants

Coral bleaching, loss of symbiotic dinoflagellate algae from the coral holobiont, is a complex phenomenon that can result in coral death and reef degradation. Reactive oxygen species (ROS) have been suggested as a possible mechanism underlying this event. To determine if antioxidants can be used to reduce ROS production and coral bleaching, we tested the effects of thermal stress in Aiptasia pallida a model system for coral bleaching studies, and the scleractinian coral, Porites astreoides. We analyzed host ROS levels, symbiont dark-adapted quantum yield of photosystem II, and symbiont loss in the presence or absence of antioxidants. We found that a single dose of the antioxidant catechin, significantly reduced ROS levels in the hosts, mitigated the degradation of the symbionts quantum yield and reduced the loss of symbionts from thermally stressed P. astreoides but not from A. pallida. Taken together, these results support a key role of ROS and that antioxidants can prevent symbiont degradation and loss during thermally-induced bleaching in P. astreoides.

Comparative demography elucidates the longevity of parasitic and symbiotic relationships

Parasitic and symbiotic relationships govern vast nutrient and energy flows1,2, but controversy surrounds their longevity. Enduring relationships may engender parallel phylogenies among hosts and parasites3,4, but so may more ephemeral relationships when parasites disproportionately colonize related hosts5. When considering these relationships’ temporal durability, it would be useful to understand whether parasite and host populations have grown and contracted in concert. Here, we devised methods to compare demographic histories, derived from genomic data6. We used these methods to compare the historical growth of the agent of severe human malaria, Plasmodium falciparum, to human and primate histories7,8 and to that of their mosquito vector Anopheles gambiae9, thereby discerning long-term parallels and anthropogenic population explosions10,11. The growth history of Trichinella spiralis, a zoonotic parasite disseminated by swine domestication12,13, proved regionally-specific, paralleling distinctive growth histories for wild boar in Asia and Europe14. Parallel histories were inferred for an anemone and its algal symbiont (Aiptasia pallida15 and Symbiodinium minutum16). Concerted growth in potatoes and the agent of potato blight (Solanum tuberosum17 and Phytophthora infestans18) did not commence until the age of potato domestication, helping date the acquisition of this historically consequential fungal plant pathogen. Therefore, comparative historical demography provides a powerful new means by which to interrogate the history of myriad ecological relationships, enriching our understanding of their origins and durability.

Actividad hemolítica de la Anémona Marina Aiptasia Pallida (Cnidaria: Actiniaria: Actiniidae) de Costa Rica

El filo Cnidaria incluye organismos considerados dentro de los más venenosos en la naturaleza. Más específicamente, alrededor de 32 especies de anémonas marinas han sido reportadas como productoras de péptidos y proteínas citolíticas. Este estudio fue llevado a cabo para evaluar la actividad hemolítica del extracto crudo de la anémona marina Aiptasia pallida en Costa Rica. El material biológico fue colectado, triturado, homogenizado y posteriormente centrifugado para la obtención del extracto crudo. El mismo fue caracterizado a través de una evaluación de su actividad hemolítica (HA) con glóbulos rojos de sangre humana (RBC). Interesantemente, los resultados de HA no mostraron rompimiento de los eritrocitos, sin embargo hubo un incremento de la absorbancia en función del tiempo. El extracto crudo reveló la existencia de una banda de proteína alrededor de 30 kDa por SDS-PAGE, no se encontró banda características de actinoporinas en A. pallida. Estos resultados podrían estar asociados con una concentración sub-lítica de otra familia de proteínas las cuales alteran el equilibrio osmótico y cambian el volumen de las células, sin un efecto letal a las concentraciones ensayadas.

A diverse host thrombospondin-type-1 repeat protein repertoire promotes symbiont colonization during establishment of cnidarian-dinoflagellate symbiosis

The mutualistic endosymbiosis between cnidarians and dinoflagellates is mediated by complex inter-partner signaling events, where the host cnidarian innate immune system plays a crucial role in recognition and regulation of symbionts. To date, little is known about the diversity of thrombospondin-type-1 repeat (TSR) domain proteins in basal metazoans or their potential role in regulation of cnidarian-dinoflagellate mutualisms. We reveal a large and diverse repertoire of TSR proteins in seven anthozoan species, and show that in the model sea anemone Aiptasia pallida the TSR domain promotes colonization of the host by the symbiotic dinoflagellate Symbiodinium minutum. Blocking TSR domains led to decreased colonization success, while adding exogenous TSRs resulted in a ‘super colonization’. Furthermore, gene expression of TSR proteins was highest at early time-points during symbiosis establishment. Our work characterizes the diversity of cnidarian TSR proteins and provides evidence that these proteins play an important role in the establishment of cnidarian-dinoflagellate symbiosis.