Chloroplast acquisition without the gene transfer in kleptoplastic sea slugs, Plakobranchus ocellatus

Examining interactions of animal cells with chloroplasts and their light-induced responses in in vitro cell culture systems

Chloroplasts are organelles that convert light energy into chemical energy in plants. The potential to integrate chloroplasts into animal cells presents an exciting frontier in synthetic biology, allowing for photo-controllable biochemical processes within these cells. However, the lack of well-established in vitro experimental systems to study chloroplast-animal cell interactions remains a significant challenge. This study investigates the behavior of human cervical cancer HeLa cells and mouse macrophage-like J774.1 cells, along with the light-induced responses of these cells, when introduced into culture media containing spinach-derived chloroplasts. Additionally, we examine isolated cells from Elysia marginata, a sacoglossan sea slug known for its unique ability to acquire and retain functional chloroplasts through a process known as kleptoplasty. Our results show that HeLa cells primarily adhere to chloroplasts with minimal intracellular uptake, while J774.1 cells actively engulf them. Co-incubation with chloroplasts increases the rate of cell death upon light irradiation. In contrast, naturally chloroplast-containing cells from E. marginata exhibit minimal light-induced damage. Excessive reactive oxygen species (ROS) production is observed in HeLa and J774.1 cells co-incubated with chloroplasts under light exposure, suggesting that photoinduced ROS generation contributes to cytotoxicity. These findings highlight three different patterns of interactions between animal cells and chloroplasts and underscore the importance of considering ROS generation induced by light exposure when analyzing chloroplast-animal cell interactions in vitro experimental systems.

Long-term functional kleptoplasty in benthic foraminifera

Foraminifera are highly diverse rhizarian protists, with some lineages having developed the ability to retain chloroplasts from algal prey (kleptoplasty). Recently, we revealed the evolutionary relationship between kleptoplasty and algal symbiosis in the benthic foraminifera Hauerina diversa. In this study, we explored fundamental aspects of host-kleptoplast interactions. The photosynthetic rates of H. diversa show the sequestered kleptoplast activity under a wide range of light intensities with no signs of photoinhibition. This lack of photoinhibition response may be attributed to the loss of key elements responsible for this process during the acquisition of kleptoplasts. Our study demonstrates the stability and notably extended retention of kleptoplasty in H. diversa, evidenced by its plastid retention under conditions of heterotrophic feeding deprivation for 50 days. The host-kleptoplast interactions suggest that H. diversa is highly committed to this partnership and that this kleptoplasty species likely relies on similar kleptoplast/alga maintenance mechanisms as symbiont-bearing foraminifera.

Advances in euglenoid genomics: unravelling the fascinating biology of a complex clade

Euglenids have long been studied due to their unique physiology and versatile metabolism, providing underpinnings for much of our understanding of photosynthesis and biochemistry, and a growing opportunity in biotechnology. Until recently there has been a lack of genetic studies due to their large and complex genomes, but recently new technologies have begun to unveil their genetic capabilities. Whilst much research has focused on the model organism Euglena gracilis, other members of the euglenids have now started to receive due attention. Currently only poor nuclear genome assemblies of E. gracilis and Rhabdomonas costata are available, but there are many more plastid genome sequences and an increasing number of transcriptomes. As more assemblies become available, there are great opportunities to understand the fundamental biology of these organisms and to exploit them for biotechnology.

Incorporation of photosynthetically active algal chloroplasts in cultured mammalian cells towards photosynthesis in animals

Chloroplasts are photosynthetic organelles that evolved through the endosymbiosis between cyanobacteria-like symbionts and hosts. Many studies have attempted to isolate intact chloroplasts to analyze their morphological characteristics and photosynthetic activity. Although several studies introduced isolated chloroplasts into the cells of different species, their photosynthetic activities have not been confirmed. In this study, we isolated photosynthetically active chloroplasts from the primitive red alga Cyanidioschyzon merolae and incorporated them in cultured mammalian cells via co-cultivation. The incorporated chloroplasts retained their thylakoid structure in intracellular vesicles and were maintained in the cytoplasm, surrounded by the mitochondria near the nucleus. Moreover, the incorporated chloroplasts maintained electron transport activity of photosystem II in cultured mammalian cells for at least 2 days after the incorporation. Our top-down synthetic biology-based approach may serve as a foundation for creating artificially photosynthetic animal cells.

Chromosome-level genome assembly of the sacoglossan sea slug Elysia timida (Risso, 1818)

BACKGROUND

Sequencing and annotating genomes of non-model organisms helps to understand genome architecture, the genetic processes underlying species traits, and how these genes have evolved in closely-related taxa, among many other biological processes. However, many metazoan groups, such as the extremely diverse molluscs, are still underrepresented in the number of sequenced and annotated genomes. Although sequencing techniques have recently improved in quality and quantity, molluscs are still neglected due to difficulties in applying standardized protocols for obtaining genomic data.

RESULTS

In this study, we present the chromosome-level genome assembly and annotation of the sacoglossan sea slug species Elysia timida, known for its ability to store the chloroplasts of its food algae. In particular, by optimizing the long-read and chromosome conformation capture library preparations, the genome assembly was performed using PacBio HiFi and Arima HiC data. The scaffold and contig N50s, at 41.8 Mb and 1.92 Mb, respectively, are approximately 30-fold and fourfold higher compared to other published sacoglossan genome assemblies. Structural annotation resulted in 19,904 protein-coding genes, which are more contiguous and complete compared to publicly available annotations of Sacoglossa with respect to metazoan BUSCOs. We found no evidence for horizontal gene transfer (HGT), i.e. no photosynthetic genes encoded in the sacoglossan nucleus genome. However, we detected genes encoding polyketide synthases in E. timida, indicating that polypropionates are produced. HPLC-MS/MS analysis confirmed the presence of a large number of polypropionates, including known and yet uncharacterised compounds.

CONCLUSIONS

We can show that our methodological approach helps to obtain a high-quality genome assembly even for a "difficult-to-sequence" organism, which may facilitate genome sequencing in molluscs. This will enable a better understanding of complex biological processes in molluscs, such as functional kleptoplasty in Sacoglossa, by significantly improving the quality of genome assemblies and annotations.

Food shaped photosynthesis: Photophysiology of the sea slug Elysia viridis fed with two alternative chloroplast donors

Background

Some Sacoglossa sea slugs steal and integrate chloroplasts derived from the algae they feed on into their cells where they continue to function photosynthetically, a process termed kleptoplasty. The stolen chloroplasts - kleptoplasts - can maintain their functionality up to several months and support animal metabolism. However, chloroplast longevity can vary depending on sea slug species and algal donor. In this study, we focused on Elysia viridis, a polyphagous species that is mostly found associated with the macroalga Codium tomentosum, but that was reported to eat other macroalgae, including Chaetomorpha sp.

Methods

We have investigated the changes in E. viridis physiology when provided with the two different food sources to evaluate to which extent the photosynthetic and photoprotective mechanisms of the algae chloroplasts matched those of the plastids once in the animal cells. To perform the study, we rely on the evaluation of chlorophyll a variable fluorescence to study the photophysiological state of the integrated kleptoplasts and high-performance liquid chromatography (HPLC) to study variations in the photosynthetic pigments.

Results

We observed that the photosynthetic efficiency of E. viridis is lower when fed with Chaetomorpha. Also, significant differences were observed in the non-photochemical quenching (NPQ) abilities of the sea slugs. While sea slugs fed with C. tomentosum react similarly to high-light stress as the alga, E. viridis hosting Chaetomorpha chloroplasts were unable to properly recover from photoinhibition or perform a functional xanthophyll cycle (XC).

Conclusions

Our results showed that, even if the sea slugs fed with the two algae show photosynthetic activities like the respective algal donors, not all the photoprotective mechanisms present in Chaetomorpha can be maintained in E. viridis. This indicates that the functionality of the kleptoplasts does not depend solely on their origin but also on the degree of compatibility with the animal species integrating them.

Food shaped photosynthesis: Photophysiology of the sea slug Elysia viridis fed with two alternative chloroplast donors

BACKGROUND

Some Sacoglossa sea slugs steal and integrate chloroplasts derived from the algae they feed on into their cells where they continue to function photosynthetically, a process termed kleptoplasty. The stolen chloroplasts - kleptoplasts - can maintain their functionality up to several months and support animal metabolism. However, chloroplast longevity can vary depending on sea slug species and algal donor. In this study, we focused on Elysia viridis, a polyphagous species that is mostly found associated with the macroalga Codium tomentosum, but that was reported to eat other macroalgae, including Chaetomorpha sp.

METHODS

We have investigated the changes in E. viridis physiology when provided with the two different food sources to evaluate to which extent the photosynthetic and photoprotective mechanisms of the algae chloroplasts matched those of the plastids once in the animal cells. To perform the study, we rely on the evaluation of chlorophyll a variable fluorescence to study the photophysiological state of the integrated kleptoplasts and high-performance liquid chromatography (HPLC) to study variations in the photosynthetic pigments.

RESULTS

We observed that the photosynthetic efficiency of E. viridis is lower when fed with Chaetomorpha. Also, significant differences were observed in the non-photochemical quenching (NPQ) abilities of the sea slugs. While sea slugs fed with C. tomentosum react similarly to high-light stress as the alga, E. viridis hosting Chaetomorpha chloroplasts were unable to properly recover from photoinhibition or perform a functional xanthophyll cycle (XC).

CONCLUSIONS

Our results showed that, even if the sea slugs fed with the two algae show photosynthetic activities like the respective algal donors, not all the photoprotective mechanisms present in Chaetomorpha can be maintained in E. viridis. This indicates that the functionality of the kleptoplasts does not depend solely on their origin but also on the degree of compatibility with the animal species integrating them.

The genome and transcriptome of the snail Biomphalaria sudanica s.l.: immune gene diversification and highly polymorphic genomic regions in an important African vector of Schistosoma mansoni

BACKGROUND

Control and elimination of schistosomiasis is an arduous task, with current strategies proving inadequate to break transmission. Exploration of genetic approaches to interrupt Schistosoma mansoni transmission, the causative agent for human intestinal schistosomiasis in sub-Saharan Africa and South America, has led to genomic research of the snail vector hosts of the genus Biomphalaria. Few complete genomic resources exist, with African Biomphalaria species being particularly underrepresented despite this being where the majority of S. mansoni infections occur. Here we generate and annotate the first genome assembly of Biomphalaria sudanica sensu lato, a species responsible for S. mansoni transmission in lake and marsh habitats of the African Rift Valley. Supported by whole-genome diversity data among five inbred lines, we describe orthologs of immune-relevant gene regions in the South American vector B. glabrata and present a bioinformatic pipeline to identify candidate novel pathogen recognition receptors (PRRs).

RESULTS

De novo genome and transcriptome assembly of inbred B. sudanica originating from the shoreline of Lake Victoria (Kisumu, Kenya) resulted in a haploid genome size of ~ 944.2 Mb (6,728 fragments, N50 = 1.067 Mb), comprising 23,598 genes (BUSCO = 93.6% complete). The B. sudanica genome contains orthologues to all described immune genes/regions tied to protection against S. mansoni in B. glabrata, including the polymorphic transmembrane clusters (PTC1 and PTC2), RADres, and other loci. The B. sudanica PTC2 candidate immune genomic region contained many PRR-like genes across a much wider genomic region than has been shown in B. glabrata, as well as a large inversion between species. High levels of intra-species nucleotide diversity were seen in PTC2, as well as in regions linked to PTC1 and RADres orthologues. Immune related and putative PRR gene families were significantly over-represented in the sub-set of B. sudanica genes determined as hyperdiverse, including high extracellular diversity in transmembrane genes, which could be under pathogen-mediated balancing selection. However, no overall expansion in immunity related genes was seen in African compared to South American lineages.

CONCLUSIONS

The B. sudanica genome and analyses presented here will facilitate future research in vector immune defense mechanisms against pathogens. This genomic/transcriptomic resource provides necessary data for the future development of molecular snail vector control/surveillance tools, facilitating schistosome transmission interruption mechanisms in Africa.

A chromosome-level genome for the nudibranch gastropod Berghia stephanieae helps parse clade-specific gene expression in novel and conserved phenotypes

BACKGROUND

How novel phenotypes originate from conserved genes, processes, and tissues remains a major question in biology. Research that sets out to answer this question often focuses on the conserved genes and processes involved, an approach that explicitly excludes the impact of genetic elements that may be classified as clade-specific, even though many of these genes are known to be important for many novel, or clade-restricted, phenotypes. This is especially true for understudied phyla such as mollusks, where limited genomic and functional biology resources for members of this phylum have long hindered assessments of genetic homology and function. To address this gap, we constructed a chromosome-level genome for the gastropod Berghia stephanieae (Valdés, 2005) to investigate the expression of clade-specific genes across both novel and conserved tissue types in this species.

RESULTS

The final assembled and filtered Berghia genome is comparable to other high-quality mollusk genomes in terms of size (1.05 Gb) and number of predicted genes (24,960 genes) and is highly contiguous. The proportion of upregulated, clade-specific genes varied across tissues, but with no clear trend between the proportion of clade-specific genes and the novelty of the tissue. However, more complex tissue like the brain had the highest total number of upregulated, clade-specific genes, though the ratio of upregulated clade-specific genes to the total number of upregulated genes was low.

CONCLUSIONS

Our results, when combined with previous research on the impact of novel genes on phenotypic evolution, highlight the fact that the complexity of the novel tissue or behavior, the type of novelty, and the developmental timing of evolutionary modifications will all influence how novel and conserved genes interact to generate diversity.

A reference genome for the long-term kleptoplast-retaining sea slug Elysia crispata morphotype clarki

Several species of sacoglossan sea slugs possess the incredible ability to sequester chloroplasts from the algae they consume. These "photosynthetic animals" incorporate stolen chloroplasts, called kleptoplasts, into the epithelial cells of tubules that extend from their digestive tracts throughout their bodies. The mechanism by which these slugs maintain functioning kleptoplasts in the absence of an algal nuclear genome is unknown. Here, we report a draft genome of the sacoglossan slug Elysia crispata morphotype clarki, a morphotype native to the Florida Keys that can retain photosynthetically active kleptoplasts for several months without feeding. We used a combination of Oxford Nanopore Technologies long reads and Illumina short reads to produce a 786-Mb assembly (N50 = 0.459 Mb) containing 68,514 predicted protein-coding genes. A phylogenetic analysis found no evidence of horizontal acquisition of genes from algae. We performed gene family and gene expression analyses to identify E. crispata genes unique to kleptoplast-containing slugs that were more highly expressed in fed versus unfed developmental life stages. Consistent with analyses in other kleptoplastic slugs, our investigation suggests that genes encoding lectin carbohydrate-binding proteins and those involved in regulation of reactive oxygen species and immunity may play a role in kleptoplast retention. Lastly, we identified four polyketide synthase genes that could potentially encode proteins producing UV- and oxidation-blocking compounds in slug cell membranes. The genome of E. crispata is a quality resource that provides potential targets for functional analyses and enables further investigation into the evolution and mechanisms of kleptoplasty in animals.

The genome and transcriptome of the snail Biomphalaria sudanica s.l.: Immune gene diversification and highly polymorphic genomic regions in an important African vector of Schistosoma mansoni

Background

Control and elimination of schistosomiasis is an arduous task, with current strategies proving inadequate to break transmission. Exploration of genetic approaches to interrupt Schistosoma mansoni transmission, the causative agent for human intestinal schistosomiasis in sub-Saharan Africa and South America, has led to genomic research of the snail vector hosts of the genus Biomphalaria. Few complete genomic resources exist, with African Biomphalaria species being particularly underrepresented despite this being where the majority of S. mansoni infections occur. Here we generate and annotate the first genome assembly of Biomphalaria sudanica sensu lato, a species responsible for S. mansoni transmission in lake and marsh habitats of the African Rift Valley. Supported by whole-genome diversity data among five inbred lines, we describe orthologs of immune-relevant gene regions in the South American vector B. glabrata and present a bioinformatic pipeline to identify candidate novel pathogen recognition receptors (PRRs).

Results

De novo genome and transcriptome assembly of inbred B. sudanica originating from the shoreline of Lake Victoria (Kisumu, Kenya) resulted in a haploid genome size of ~944.2 Mb (6732 fragments, N50=1.067 Mb), comprising 23,598 genes (BUSCO=93.6% complete). The B. sudanica genome contains orthologues to all described immune genes/regions tied to protection against S. mansoni in B. glabrata. The B. sudanica PTC2 candidate immune genomic region contained many PRR-like genes across a much wider genomic region than has been shown in B. glabrata, as well as a large inversion between species. High levels of intra-species nucleotide diversity were seen in PTC2, as well as in regions linked to PTC1 and RADres orthologues. Immune related and putative PRR gene families were significantly over-represented in the sub-set of B. sudanica genes determined as hyperdiverse, including high extracellular diversity in transmembrane genes, which could be under pathogen-mediated balancing selection. However, no overall expansion in immunity related genes were seen in African compared to South American lineages.

Conclusions

The B. sudanica genome and analyses presented here will facilitate future research in vector immune defense mechanisms against pathogens. This genomic/transcriptomic resource provides necessary data for the future development of molecular snail vector control/surveillance tools, facilitating schistosome transmission interruption mechanisms in Africa.

A 1.5-Mb continuous endogenous viral region in the arbuscular mycorrhizal fungus Rhizophagus irregularis

Most fungal viruses are RNA viruses, and no double-stranded DNA virus that infects fungi is known to date. A recent study detected DNA polymerase genes that originated from large dsDNA viruses in the genomes of basal fungi, suggestive of the existence of dsDNA viruses capable of infecting fungi. In this study, we searched for viral infection signatures in chromosome-level genome assemblies of the arbuscular mycorrhizal fungus Rhizophagus irregularis. We identified a continuous 1.5-Mb putative viral region on a chromosome in R. irregularis strain 4401. Phylogenetic analyses revealed that the viral region is related to viruses in the family Asfarviridae of the phylum Nucleocytoviricota. This viral region was absent in the genomes of four other R. irregularis strains and had fewer signals of fungal transposable elements than the other genomic regions, suggesting a recent and single insertion of a large dsDNA viral genome in the genome of this fungal strain. We also incidentally identified viral-like sequences in the genome assembly of the sea slug Elysia marginata that are evolutionally close to the 1.5-Mb putative viral region. In conclusion, our findings provide strong evidence of the recent infection of the fungus by a dsDNA virus.

Whole Genome Duplication and Gene Evolution in the Hyperdiverse Venomous Gastropods

The diversity of venomous organisms and the toxins they produce have been increasingly investigated, but taxonomic bias remains important. Neogastropods, a group of marine predators representing almost 22% of the known gastropod diversity, evolved a wide range of feeding strategies, including the production of toxins to subdue their preys. However, whether the diversity of these compounds is at the origin of the hyperdiversification of the group and how genome evolution may correlate with both the compounds and species diversities remain understudied. Among the available gastropods genomes, only eight, with uneven quality assemblies, belong to neogastropods. Here, we generated chromosome-level assemblies of two species belonging to the Tonnoidea and Muricoidea superfamilies (Monoplex corrugatus and Stramonita haemastoma). The two obtained high-quality genomes had 3 and 2.2 Gb, respectively, and 92-89% of the total assembly conformed 35 pseudochromosomes in each species. Through the analysis of syntenic blocks, Hox gene cluster duplication, and synonymous substitutions distribution pattern, we inferred the occurrence of a whole genome duplication event in both genomes. As these species are known to release venom, toxins were annotated in both genomes, but few of them were found in homologous chromosomes. A comparison of the expression of ohnolog genes (using transcriptomes from osphradium and salivary glands in S. haemastoma), where both copies were differentially expressed, showed that most of them had similar expression profiles. The high quality of these genomes makes them valuable reference in their respective taxa, facilitating the identification of genome-level processes at the origin of their evolutionary success.

Genome assembly of the Korean intertidal mud-creeper Batillaria attramentaria

Batillaridae is a common gastropod family that occurs abundantly in the shallow coastal zone of the intertidal mudflats of the northwest Pacific Ocean, Australasia, and North America. In this family, Batillaria attramentaria is known for its biological invasion and colonization in estuarine and intertidal zones. It can endure and adapt the harsh intertidal conditions such as frequent temperature alteration, salinity, and air exposure. Therefore, we sequenced and assembled this Korean batillariid genome to get insight into its intertidal adaptive features. Approximately 53 Gb of DNA sequences were generated, and 863 scaffolds were assembled into a draft genome of 0.715 Gb with 97.1% BUSCO completeness value. A total of 40,596 genes were predicted. We estimated that B. attramentaria and Conus consors diverged about 230 million years ago (MYA) based on the phylogenetic analysis of closely related gastropod species. This genome study sets the footstep for genomics studies among native and introduced Batillaria populations and the Batillaridae family members.

Identification of three elevenin receptors and roles of elevenin disulfide bond and residues in receptor activation in Aplysia californica

Neuropeptides are ubiquitous intercellular signaling molecules in the CNS and play diverse roles in modulating physiological functions by acting on specific G-protein coupled receptors (GPCRs). Among them, the elevenin signaling system is now believed to be present primarily in protostomes. Although elevenin was first identified from the L11 neuron of the abdominal ganglion in mollusc Aplysia californica, no receptors have been described in Aplysia, nor in any other molluscs. Here, using two elevenin receptors in annelid Platynereis dumerilii, we found three putative elevenin GPCRs in Aplysia. We cloned the three receptors and tentatively named them apElevR1, apElevR2, and apElevR3. Using an inositol monophosphate (IP1) accumulation assay, we demonstrated that Aplysia elevenin with the disulfide bond activated the three putative receptors with low EC50 values (ranging from 1.2 to 25 nM), supporting that they are true receptors for elevenin. In contrast, elevenin without the disulfide bond could not activate the receptors, indicating that the disulfide bond is required for receptor activity. Using alanine substitution of individual conserved residues other than the two cysteines, we showed that these residues appear to be critical to receptor activity, and the three different receptors had different sensitivities to the single residue substitution. Finally, we examined the roles of those residues outside the disulfide bond ring by removing these residues and found that they also appeared to be important to receptor activity. Thus, our study provides an important basis for further study of the functions of elevenin and its receptors in Aplysia and other molluscs.

Outer fold is sole effective tissue among three mantle folds with regard to oyster shell colour

Molluscs constitute the second largest phylum of animals in the world, and shell colour is one of their most important phenotypic characteristics. In this study, we found among three folds on the mantle edge of oyster, only the outer fold had the same colour as the shell. Transcriptome and mantle cutting experiment indicated that the outer fold may be mainly reflected in chitin framework formation and biomineralisation. There were obvious differences in SEM structure and protein composition between the black and white shell periostraca. The black shell periostraca had more proteins related to melanin biosynthesis and chitin binding. Additionally, we identified an uncharacterized protein gene (named as CgCBP) ultra-highly expressed only in the black outer fold and confirmed its function of chitin-binding and CaCO₃ precipitation promoting. RNAi also indicated that CgCBP knockdown could change the structure of shell periostracum and reduce shell pigmentation. All these results suggest that the mantle outer fold plays multiple key roles in shell periostraca bioprocessing, and shell periostracum structure affected by chitin-binding protein is functionally correlated with shell pigmentation. The investigation of oyster shell periostracum structure and shell colour will provide a better understanding in pigmentation during biological mineralisation in molluscs.

Asfarviruses and Closely Related Giant Viruses

Acanthamoeba polyphaga mimivirus, so called because of its "mimicking microbe", was discovered in 2003 and was the founding member of the first family of giant viruses isolated from amoeba. These giant viruses, present in various environments, have opened up a previously unexplored field of virology. Since 2003, many other giant viruses have been isolated, founding new families and taxonomical groups. These include a new giant virus which was isolated in 2015, the result of the first co-culture on Vermamoeba vermiformis. This new giant virus was named "Faustovirus". Its closest known relative at that time was African Swine Fever Virus. Pacmanvirus and Kaumoebavirus were subsequently discovered, exhibiting phylogenetic clustering with the two previous viruses and forming a new group with a putative common ancestor. In this study, we aimed to summarise the main features of the members of this group of giant viruses, including Abalone Asfarvirus, African Swine Fever Virus, Faustovirus, Pacmanvirus, and Kaumoebavirus.

Effect of static magnetic field on marine mollusc Elysia leucolegnote

Artificial magnetic fields are unavoidable environment for offshore marine organisms. With the substantially increasing submarine cables, the impact of magnetic field generated by cables on marine organisms has gradually attracted people's attention. However, there are few studies on the effect of magnetic field on molluscs. To explore whether magnetic fields could interfere with the physiological functions of offshore molluscs, here we systematically analyzed the change of metabolism and transcriptome of Elysia leucolegnote exposed to either geomagnetic field or 1.1 T static magnetic field. The blood glucose and lipid levels, as well as the activities of antioxidant enzymes in E. leucolegnote were significantly increased upon the exposure to high static magnetic field for 10 days. Meanwhile, the activities of enzymes related to digestive performance and liver functions were decreased. Possible mechanisms were further revealed through comparative transcriptome analysis. A total of 836 differentially expressed genes were identified, 352 of which were up-regulated and 484 of which were down-regulated after exposure to the high static magnetic field. The up-regulated differential genes were mainly concentrated in lysosomal and apoptotic pathways, and down-regulated differential genes were mainly involved in digestive and immune systems including phagocytosis. This pattern was further confirmed by RT-qPCR analysis. In conclusion, prolonged exposure to a 1.1 T static magnetic field increased oxidative stress and blood glucose and lipid levels, and decreased immunity and physiological conditions in E. leucolegnote. The data we presented here provides a comprehensive view of metabolism change and gene expression pattern of E. leucolegnote exposed to static magnetic field. It may expand our knowledge on the magnetic field effects on offshore mollusc at molecular level, and contribute to clarification of the interaction between marine animals and artificial magnetic fields, which is certainly ecologically important.

Kleptoplasty: Getting away with stolen chloroplasts

Kleptoplasty, the process by which a host organism sequesters and retains algal chloroplasts, is relatively common in protists. The origin of the plastid varies, as do the length of time it is retained in the host and the functionality of the association. In metazoa, the capacity for long-term (several weeks to months) maintenance of photosynthetically active chloroplasts is a unique characteristic of a handful of sacoglossan sea slugs. This capability has earned these slugs the epithets "crawling leaves" and "solar-powered sea slugs." This Unsolved Mystery explores the basis of chloroplast maintenance and function and attempts to clarify contradictory results in the published literature. We address some of the mysteries of this remarkable association. Why are functional chloroplasts retained? And how is the function of stolen chloroplasts maintained without the support of the algal nucleus?

How many single-copy orthologous genes from whole genomes reveal deep gastropod relationships?

The Gastropoda contains 80% of existing mollusks and is the most diverse animal class second only to the Insecta. However, the deep phylogeny of gastropods has been controversial for a long time. Especially the position of Patellogastropoda is a major uncertainty. Morphology and some mitochondria studies concluded that Patellogastropoda is likely to be sister to all other gastropods (Orthogastropoda hypothesis), while transcriptomic and other mitogenomic studies indicated that Patellogastropoda and Vetigastropoda are sister taxa (Psilogastropoda). With the release of high-quality genomes, orthologous genes can be better identified and serve as powerful candidates for phylogenetic analysis. The question is, given the current limitations on the taxon sampling side, how many markers are needed to provide robust results. Here, we identified single-copy orthologous genes (SOGs) from 14 gastropods species with whole genomes available which cover five main gastropod subclasses. We generated different datasets from 395 to 1610 SOGs by allowing species missing in different levels. We constructed gene trees of each SOG, and inferred species trees from different collections of gene trees. We found as the number of SOGs increased, the inferred topology changed from Patellogastropoda being sister to all other gastropods to Patellogastropoda being sister to Vetigastropoda + Neomphalina (Psilogastropoda s.l.), with considerable support. Our study thus rejects the Orthogastropoda concept showing that the selection of the representative species and use of sufficient informative sites greatly influence the analysis of deep gastropod phylogeny.

Acquisition of bioluminescent trait by non-luminous organisms from luminous organisms through various origins

Bioluminescence is a natural light emitting phenomenon that occurs due to a chemical reaction between luciferin and luciferase. It is primarily an innate and inherited trait in most terrestrial luminous organisms. However, most luminous organisms produce light in the ocean by acquiring luminous symbionts, luciferin (substrate), and/or luciferase (enzyme) through various transmission pathways. For instance, coelenterazine, a well-known luciferin, is obtained by cnidarians, crustaceans, and deep-sea fish through multi-level dietary linkages from coelenterazine producers such as ctenophores, decapods, and copepods. In contrast, some non-luminous Vibrio bacteria became bioluminescent by obtaining lux genes from luminous Vibrio species by horizontal gene transfer. Various examples detailed in this review show how non-luminescent organisms became luminescent by acquiring symbionts, dietary luciferins and luciferases, and genes. This review highlights three modes (symbiosis, ingestion, and horizontal gene transfer) that allow organisms lacking genes for autonomous bioluminescent systems to obtain the ability to produce light. In addition to bioluminescence, this manuscript discusses the acquisition of other traits such as pigments, fluorescence, toxins, and others, to infer the potential processes of acquisition.

Photosynthesis from stolen chloroplasts can support sea slug reproductive fitness

Some sea slugs are able to steal functional chloroplasts (kleptoplasts) from their algal food sources, but the role and relevance of photosynthesis to the animal host remain controversial. While some researchers claim that kleptoplasts are slowly digestible 'snacks', others advocate that they enhance the overall fitness of sea slugs much more profoundly. Our analysis shows light-dependent incorporation of 13C and 15N in the albumen gland and gonadal follicles of the sea slug Elysia timida, representing translocation of photosynthates to kleptoplast-free reproductive organs. Long-chain polyunsaturated fatty acids with reported roles in reproduction were produced in the sea slug cells using labelled precursors translocated from the kleptoplasts. Finally, we report reduced fecundity of E. timida by limiting kleptoplast photosynthesis. The present study indicates that photosynthesis enhances the reproductive fitness of kleptoplast-bearing sea slugs, confirming the biological relevance of this remarkable association between a metazoan and an algal-derived organelle.