Transcriptome sequencing of sea cucumber (Apostichopus japonicus) and the identification of gene-associated markers

Morpho-functional characterisation of cœlomocytes in the aquacultivated sea cucumber Holothuria scabra: From cell diversity to transcriptomic immune response

Holothuria scabra is one of the most valuable species of sea cucumber owing to its exploitation as a seafood product. This study aims to describe the main molecular and cellular actors in the immunology of this species. First, a detailed description of the immune cells - the cœlomocytes - is provided, highlighting five main cell types including phagocytes, small round cells (SRCs), spherulocytes, fusiform cells, and crystal cells, with a further five subtypes identified using transmission electron microscopy. Cœlomocyte aggregates were also described morphologically, yielding two main types, one comprising three successive maturation stages. A comparison of the concentration and proportion of cell populations was carried out between the two main body fluids, namely the hydrovascular fluid of the Polian vesicle (HF) and the perivisceral fluid of the general cavity (PF), and no clear relation could be highlighted. Next, the cœlomocyte immune response was studied 24 h after lipopolysaccharide (LPS) injection in the two body fluids. Firstly, the fluctuation in cell populations was assessed, and despite a high inter-individual variability, it shows a decrease in the phagocyte proportion and an increase in the SRC proportion. Secondly, the differential gene expression of PF cœlomocytes was studied by de novo RNA-sequencing between LPS-injected and control-injected individuals: 945 genes were differentially expressed, including 673 up-regulated and 272 down-regulated in the LPS-injected individuals. Among these genes, 80 had a presumed function in immunity based on their annotation, covering a wide range of immune mechanisms. Overall, this study reveals a complex immune system at both molecular and cellular levels and constitutes a baseline reference on H. scabra immunity, which may be useful for the development of sustainable aquaculture and provides valuable data for comparative immunology.

Genetic diversity assessment of cucumber landraces using molecular signatures

Genetic profiling of the biodiversity in cultivated crop plants is necessary to preserve important genes and utilize them in a breeding program. Cucumber is used as a model plant to study various characteristics of Cucurbitaceae. Its adaptation to a wide range of climatic conditions suggested analyzing the landraces. The present study was conducted to evaluate the differences, at the genetic level, among landraces spanning five continents. DNA extracted from fifty-six landraces selected from USDA germplasm bank to cover a global representative sample of world cucumber landraces was used for polymerase chain reaction using twenty-eight polymorphic expressed sequence tags simple sequence repeat (EST-SSR) markers. Twenty-eight EST-SSR markers covering all seven chromosomes yielded 98 bands with an average of 3.42 bands per marker. Polymorphic information content ranged from 0.00 (EC35) to 0.74 (EC17) with an average of 0.34. Six clusters provided an appropriate summary of the variation among the landraces, with the two largest groups including 32 (Asiatic) and 17 (European and American) landraces, respectively. Four small groups, three with two members, and one with one member (PI 525155-Egypt) were dissimilar to the two main groups. Landraces from the same region were often clustered together. Genetic similarity of the landraces was revealed by marker banding patterns. The locations of genetic diversity for cucumber landraces can be identified from this study.

Transcriptome sequencing analysis of bovine mammary epithelial cells induced by lipopolysaccharide

Mastitis in cows is caused by the inflammation of the mammary glands due to an infection by external pathogenic bacteria. Mammary gland epithelial cells, which are in direct contact with the external environment, are responsible for the first line of defense of the mammary gland against pathogenic bacteria, playing an essential role in immune defense. To investigate the mechanism of bovine mammary epithelial cells in the inflammatory process, we treated the cells with LPS for 12 hours and analyzed the changes in mRNA by transcriptome sequencing. The results showed that compared to the control group, the LPS treatment group had 121 up-regulated genes and 18 down-regulated genes. GO and KEGG enrichment analysis revealed that these differential genes were mainly enriched in the IL-17 signaling pathway, Legionellosis, Cytokine-cytokine receptor interaction, NF-kappa B signaling pathway, and other signaling pathways. Furthermore, the expression of GRO1 and CXCL3 mRNAs increased significantly after LPS treatment. These findings provide new insights for the treatment of mastitis in cows in the future.

SSR Marker Acquisition and Application from Transcriptome of Captive Chinese Forest Musk Deer (Moschus berezovskii)

Forest musk deer (Moschus berezovskii) is one of the most endangered medicinally important wild animals in the world. Forest musk deer farming is the main way of production of musk. However, the single provenance and lack of genetic information lead to reduced genetic diversity of forest musk deer. Therefore, more SSR markers need to be developed to identify forest musk deer germplasm. In this study, bone marrow derived mesenchymal cells were used to construct cDNA library for transcriptome sequencing. The datasets were de novo assembled and annotated. 9 polymorphic simple sequence repeat (SSR) markers were finally identified and used to detect population genetic diversity. 6.07 Gb clean data were generated using Illumina sequencing technology, and de novo assembled into 138,591 transcripts and 81,553 unigenes. 5,777 simple sequence repeats (SSRs) were identified, in which there were 578 repeating motif types, with mono-nucleotide and tri-nucleotides comprising 55.88% and 25.60%, respectively. 100 primer pairs were designed to validate amplification and polymorphism using DNA from fecal samples. 9 polymorphic SSRs were developed and used to detect population genetic diversity of 122 forest musk deer in 2 farms. The average number of alleles per locus varied from 4 to 15 (average = 8.3). The observed heterozygosity (HO) per locus ranged from 0.102 to 0.941, while the expected heterozygosity (HE) per locus was from 0.111 to 0.651. All loci deviated significantly from the Hardy-Weinberg equilibrium (p < 0.001). The polymorphism information content (PIC) of these loci varied from 0.108 to 0.619. 9 polymorphic SSR markers were developed in this research. These sites can be used for breeding planning and conservation of germplasm resources.

YTHDC1/CRM1 Facilitates m6A-Modified circRNA388 Nuclear Export to Induce Coelomocyte Autophagy via the miR-2008/ULK Axis in Apostichopus japonicus

N 6-methyladenosine (m6A), the most prevalent internal modification in eukaryotic RNA, was able to mediate circular RNA (circRNA) function in many immune processes. Nevertheless, the functional role of m6A-modified circRNAs in innate immunity of invertebrates remained unclear. In this study, we identified m6A-modified circRNA388 from cultured sea cucumber (Apostichopus japonicus) coelomocytes, which was mainly detected in cytoplasm after Vibrio splendidus infection. A knockdown assay indicated that cytoplasm circRNA388 promoted coelomocyte autophagy and decreased the number of intracellular V. splendidus. Mechanistically, the circRNA388 in the cytoplasm directly sponged miR-2008 to block its interaction with Unc-51-like kinase 1 from A. japonicus (AjULK) and further promoted autophagy to resist V. splendidus infection. More importantly, we found that m6A modification was vital to circRNA388 nuclear export with YTH domain-containing protein 1 from A. japonicus (AjYTHDC1) as the reader. AjYTHDC1 facilitated the nuclear export of m6A-modified circRNA388 via interaction with exportin-1 (chromosomal maintenance 1) from A. japonicus (AjCRM1). Knockdown of AjCRM1 could significantly decrease the content of cytoplasm circRNA388. Overall, our results provide the first evidence that nuclear export of m6A-modified circRNA388 is dependent on the novel AjCRM1 to our knowledge, which was further promoted coelomocyte autophagy by miR-2008/AjULK axis to clear intracellular V. splendidus.

WntA and Wnt4 during the regeneration of internal organs in the holothurian Eupentacta fraudatrix

BACKGROUND

Over the past few years, it has been established that wnt genes are involved in the regenerative processes of holothurians. The wnt4 gene was identified as one of the most active genes in Eupentacta fraudatrix regeneration using differential gene expression analysis and qPCR of individual genes. Also, the wntA gene was found in holothurians, which is present only in invertebrates and can perform unique functions.

RESULTS

In this regard, both these genes and proteins were studied in this work. During regeneration, the Wnt4 protein is found in the cells of the coelomic and ambulacral epithelium, retractor muscles, and radial nerves. Single cells with this protein are also found in the connective tissue of the developing aquapharyngeal bulb and in the hypoderm of the body wall. Cells with WntA are found exclusively in the hypoderm of the body wall.

CONCLUSION

We assume that both genes are involved in regeneration, but Wnt4 coordinates the formation of the epithelial tissue structure, while WntA maintains the state of the intercellular substance of the body wall.

A signal recognition particle receptor gene from the sea cucumber, Apostichopus japonicas

The signal recognition particle (SRP) system delivers approximately 30% of the proteome to the endoplasmic reticulum (ER) membrane. SRP receptor alpha (SRα) binds to SRP for targeting nascent secreted proteins to the ER membrane in eukaryotic cells. In this study, the SRα homologous gene was identified in the sea cucumber, Apostichopus japonicus (AjSRα). AjSRα codes for 641 amino acids and has 54.94% identity with its mammalian homologs. Like mammalian SRα, it is expected to contain the SRP-alpha N domain, SRP54_N domain, and SRP54 domain. In addition, AjSRα is ubiquitously expressed in adult tissues and exhibits a sexually dimorphic expression pattern, with significantly higher expression in ovaries compared to testes. As a maternal factor, AjSRα can be continuously detected during embryonic development. Importantly, we first attempted to investigate its function by using lentiviral vectors for delivering SRα gene-specific shRNA, and we revealed that lentiviral vectors do not induce an upregulation of immune-related enzymes in sea cucumbers. However, compared to the dsRNA-based RNA interference (RNAi) method, lentivirus-mediated RNAi caused dynamic changes in gene expression at a later time. This study supplied the technical support for studying the functional mechanism of SRα in sea cucumbers.

Transcriptome analysis of growth variation in early juvenile stage sandfish Holothuria scabra

The sandfish Holothuria scabra is a high-value tropical sea cucumber species representing a major mariculture prospect across the Indo-Pacific. Advancements in culture technology, rearing, and processing present options for augmenting capture production, stock restoration, and sustainable livelihood activities from hatchery-produced sandfish. Further improvements in mariculture production may be gained from the application of genomic technologies to improve performance traits such as growth. In this study, we performed de novo transcriptome assembly and characterization of fast- and slow-growing juvenile H. scabra from three Philippine populations. Analyses revealed 66 unigenes that were consistently differentially regulated in fast-growing sandfish and found to be associated with immune response and metabolism. Further, we identified microsatellite and single nucleotide polymorphism markers potentially associated with fast growth. These findings provide insight on potential genomic determinants underlying growth regulation in early juvenile sandfish which will be useful for further functional studies.

Transcriptome analysis reveals roles of polian vesicle in sea cucumber Apostichopus japonicus response to Vibrio splendidus infection

Polian vesicle is originally regarded as a hematopoietic and inflammatory response organ in sea cucumber by the operations of cell depletion and heterogeneous cells injection, respectively. In the present study, to reveal the role and immune mechanisms of polian vesicle in response to pathogen, Vibrio splendidus, we first performed a comparative transcriptome analysis for the cells from polian vesicle wall in V. splendidus-challenged Apostichopus japonicus through RNA high-throughput sequencing technology. Briefly, 465,356,848 clean reads were obtained after cleaning up low-quality reads in total. Approximately 73% of the sequenced reads could be aligned to the reference genome of A. japonicus. The DEGs of CG (control group) vs TG 24 h (24 h post-infection group), CG vs TG 72 h (72 h post-infection group) and TG 24 h vs TG 72 h were 3762, 1391 and 3258, respectively. Gene Ontology (GO) annotation assay revealed that those genes associated with the processes such as cell process, cell, binding and catalytic activity were significantly induced in all three groups post V. splendidus infection. KEGG enrichment analysis suggested the DEGs in TG 24 h were enriched in Toll-like receptor (TLR) signaling pathway, complement and coagulation cascades, antigen processing and presentation and IL-17 signaling pathway compared with that in CG, while the pathways including ribosome biogenesis in eukaryotes, DNA replication, and cell cycle related with cell proliferation were mainly enriched in TG 72 h than that of CG. Furthermore, six important DEGs were chosen and showed the consistent expression patterns with the results of RNA-seq by qPCR. Overall, our analysis towards the current data demonstrates that polian vesicle may play an essential role in the regulation of immune response in A. japonicus and provide new insights into hematopoietic function of polian vesicle in response to pathogen infection.

Molecular Aspects of Regeneration Mechanisms in Holothurians

Holothurians, or sea cucumbers, belong to the phylum Echinodermata. They show good regenerative abilities. The present review provides an analysis of available data on the molecular aspects of regeneration mechanisms in holothurians. The genes and signaling pathways activated during the asexual reproduction and the formation of the anterior and posterior parts of the body, as well as the molecular mechanisms that provide regeneration of the nervous and digestive systems, are considered here. Damage causes a strong stress response, the signs of which are recorded even at late regeneration stages. In holothurian tissues, the concentrations of reactive oxygen species and antioxidant enzymes increase. Furthermore, the cellular and humoral components of the immune system are activated. Extracellular matrix remodeling and Wnt signaling play a major role in the regeneration in holothurians. All available morphological and molecular data show that the dedifferentiation of specialized cells in the remnant of the organ and the epithelial morphogenesis constitute the basis of regeneration in holothurians. However, depending on the type of damage, the mechanisms of regeneration may differ significantly in the spatial organization of regeneration process, the involvement of different cell types, and the depth of reprogramming of their genome (dedifferentiation or transdifferentiation).

Enhanced protein phosphorylation in Apostichopus japonicus intestine triggered by tussah immunoreactive substances might be involved in the regulation of immune-related signaling pathways

The sea cucumber Apostichopus japonicus is an economically important species owing to its high nutritive and medicinal value. In order to avoid the pollution resulting from the overuse of antibiotics in A. japonicus aquaculture, various immunostimulants have been used as an alternative to improve the efficiency of A. japonicus farming. Our previous proteomic investigation has shown that several proteins participating in the immune-related physiology of A. japonicus were differentially expressed in the intestinal tissue in response to tussah immunoreactive substances (TIS). This study further explored the immunostimulation mechanism of TIS in A. japonicus. Phosphoproteomics technology was used to investigate the effect of TIS on protein phosphorylation in the intestine of A. japonicus following feeding with a TIS-supplemented diet. A total of 213 unique phosphoproteins were detected from 225 unique phosphopeptides. KEGG pathway analysis showed that majority of the phosphoproteins are involved in endocytosis, carbon metabolism and spliceosome functional group. Sixteen of the phosphoproteins exhibited differential phosphorylation in response to TIS and 12 of these were found to associate with biological functions. Of these 12 phosphoproteins, eight exhibited enhanced phosphorylation while four displayed reduced phosphorylation. These 12 proteins were further analyzed and all were found to play a role in regulating some aspects of the immune system and the growth of sea cucumbers, especially in phagocytosis, energy metabolism and disease resistance. The findings of this study could therefore shed new light on the immune pathways of sea cucumber that are affected by TIS. This could help us to better understand the underlying mechanism linked to the immunoenhancement of A. japonicus in response to TIS, one that is associated with the change in protein phosphorylation.

Insights into the DNA methylation of sea cucumber Apostichopus japonicus in response to skin ulceration syndrome infection

DNA methylation is an important epigenetic modification that regulates gene expression in many biological processes, including immune response. In this study, whole-genome bisulfite sequencing (WGBS) was carried out on healthy body wall (HB) and skin ulceration syndrome (SUS) infected body wall (SFB) to gain insights into the epigenetic regulatory mechanism in sea cucumber Apostichopus japonicus. After comparison, a total of 116,522 differentially methylated regions (DMRs) were obtained including 67,269 hyper-methylated and 49,253 hypo-methylated DMRs (p < 0.05, FDR < 0.001). GO enrichment analysis indicated that regulation of DNA-templated transcription (GO: 0006355), where DNA methylation occurred, was the most significant term in the biology process. The integration of methylome and transcriptome analysis revealed that 10,499 DMRs were negatively correlated with 496 differentially expressed genes (DEGs). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that these DEGs were enriched in the phosphoinositide 3-kinase-protein kinase B (PI3K/Akt)/mammalian target of rapamycin (mTOR) signaling pathway. Interestingly, two serine/threonine-protein kinases, nemo-like kinase (NLK) and mTOR, were highlighted after functional analysis. The variations of methylation in these two genes were associated with SUS infection and immune regulation. They regulated gene expression at different levels and showed interaction during response process. The validation of methylation sites showed high consistency between pyrosequencing and WGBS. WGBS analysis not only revealed the changes of DNA methylation, but also presented important information about the regulation of key genes after SUS infection in A. japonicus.

De novo leaf transcriptome assembly of Bougainvillea spectabilis for the identification of genes involves in the secondary metabolite pathways

Bougainvillea spectabilis is known as a vital medicinal, ornamental as well as an essential oil producing plant. It is also a rich source of important secondary metabolites with several therapeutic properties. Various studies on its pharmacological and toxicological aspects have been published but there is no genomic or transcriptomic resource available in the public databases. To address this important issue, the de-novo transcriptome assembly of B. spectabilis leaf tissue has been done for the identification of genes involved in various important secondary metabolites, Single nucleotide polymorphism (SNPs) and Simple sequence repeats (SSRs). The transcriptome sequencing of B. spectabilis leaf tissue generated 79,811,024 raw reads with GC value 42.77%. The transcriptomic assembly was performed by Trinity software which generated 100,374 transcripts and 99,793 unigenes with minimum and maximum length of 201 bp and 13,237 bp and N50 value of 1470 and 1472 respectively. Annotation of these unigenes was performed using seven databases including NR, PFAM, GO and KEGG. Approximately, 44,302 unigenes were annotated in GO database. The KEGG pathway analysis revealed 23,102 unigenes in which 19,054 genes were assigned to five groups in KEGG and 130 biochemical pathways. The highest group among the five groups was Metabolism with 9230 unigenes. Moreover, about 63,226 SNPs and 30,333 SSRs in the leaf transcriptome of B. spectabilis were identified. To the best of my understanding it will be the first comprehensive transcriptome analysis of B. spectabilis from family Nyctaginaceae which will help as a reference line for further genomic and transcriptomic studies.

Transcriptome analysis of sea cucumber (Apostichopus japonicus) polian vesicles in response to evisceration

Polian vesicles are considered as the site of coelomocyte formation, and play crucial roles in the inflammatory reaction in sea cucumber. After evisceration, coelomocytes and internal organs except polian vesicles are excreted. Our previous study found that the total number of coelomocytes was rapidly recovered at 6 h post-evisceration in sea cucumber Apostichopus japonicus, and this regeneration of coelomocytes might be closely related to polian vesicles. To further investigate the related-gene expression pattern of the polian vesicles at 6 h post-evisceration, the transcriptome analysis of polian vesicles was carried out. A total of 2752 differentially expressed genes (DEGs) were identified, including 1,453 up-regulated genes and 1299 down-regulated genes. Gene Ontology (GO) enrichment showed that most of the DEGs were classified under Regulation of transcription, Regulation of RNA metabolic process, Regulation of nucleic acid-templated transcription. Meanwhile, 11 significantly enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were identified. Among them, Wnt, TGF-β and Endocytosis pathways are well-related with cell proliferation and differentiation, which may be involved in the regeneration of coelomocytes in A. japonicus after evisceration. In addition, FoxO signaling pathway plays important roles in immunoregulation, in which the expression levels of the DEGs were significantly up-regulated, inferring that polian vesicles could not only participate in the coelomocyte regeneration process, but also undertake a certain immune defense function in A. japonicus after evisceration. These findings will be beneficial for understanding the mechanisms of coelomocyte regeneration and immune defense of A. japonicus after evisceration.

Characterization and analysis of the transcriptome in Gymnocypris selincuoensis on the Qinghai-Tibetan Plateau using single-molecule long-read sequencing and RNA-seq

The lakes on the Qinghai-Tibet Plateau (QTP) are the largest and highest lake group in the world. Gymnocypris selincuoensis is the only cyprinid fish living in lake Selincuo, the largest lake on QTP. However, its genetic resource is still blank, limiting studies on molecular and genetic analysis. In this study, the transcriptome of G. selincuoensis was first generated by using PacBio Iso-Seq and Illumina RNA-seq. A full-length (FL) transcriptome with 75,435 transcripts was obtained by Iso-Seq with N50 length of 3,870 bp. Among all transcripts, 75,016 were annotated to public databases, 64,710 contain complete open reading frames and 2,811 were long non-coding RNAs. Based on all- vs.-all BLAST, 2,069 alternative splicing events were detected, and 80% of them were validated by reverse transcription polymerase chain reaction (RT-PCR). Tissue gene expression atlas showed that the number of detected expressed transcripts ranged from 37,397 in brain to 19,914 in muscle, with 10,488 transcripts detected in all seven tissues. Comparative genomic analysis with other cyprinid fishes identified 77 orthologous genes with potential positive selection (Ka/Ks > 0.3). A total of 56,696 perfect simple sequence repeats were identified from FL transcripts. Our results provide valuable genetic resources for further studies on adaptive evolution, gene expression and population genetics in G. selincuoensis and other congeneric fishes.

Comparative physiology and aquaculture: Toward Omics-enabled improvement of aquatic animal health and sustainable production

Omics-technologies have revolutionized biomedical research over the past two decades, and are now poised to play a transformative role in aquaculture. This article serves as an introduction to a Virtual Special Issue of Comparative Biochemistry and Physiology - Part D: Genomics and Proteomics (CBPD), with the objective to showcase the state-of-the-science for Omics in aquaculture. In this editorial, we describe the role that Omics can play in aquaculture, and provide a synopsis for each of the Special Issue articles that use these technologies to improve aquaculture practices. Current genomic resources available for some aquaculture species are also described. The number of datasets is impressive for species such as Atlantic salmon and rainbow trout, totaling in the thousands (NCBI Gene Expression Omnibus and Sequence Read Archive). We present a conceptual framework that describes how Omics can be leveraged to understand complex responses of aquatic animals in culture for relevant physiological outcomes, such as fecundity, growth, and immunity. Lastly, knowledge gaps and new directions are identified to address current obstacles in aquaculture. Articles in this Special Issue on aquaculture in CBPD highlight the diversity and scope of Omics in aquaculture. As the technology becomes more cost-effective, it is anticipated that genomics, transcriptomics, proteomics, metabolomics and lipidomics will play increasingly important roles in stock diagnostics (e.g. genetics, health, performance). The timing is right, as global concerns are reaching critical levels over food availability/security and water restrictions for humankind.

RNA Sequencing Analysis to Capture the Transcriptome Landscape during Tenderization in Sea Cucumber Apostichopus japonicus

Sea cucumber (Apostichopus japonicus) is an economically significant species in China having great commercial value. It is challenging to maintain the textural properties during thermal processing due to the distinctive physiochemical structure of the A. japonicus body wall (AJBW). In this study, the gene expression profiles associated with tenderization in AJBW were determined at 0 h (CON), 1 h (T_1h), and 3 h (T_3h) after treatment at 37 °C using Illumina HiSeq™ 4000 platform. Seven-hundred-and-twenty-one and 806 differentially expressed genes (DEGs) were identified in comparisons of T_1h vs. CON and T_3h vs. CON, respectively. Among these DEGs, we found that two endogenous proteases-72 kDa type IV collagenase and matrix metalloproteinase 16 precursor-were significantly upregulated that could directly affect the tenderness of AJBW. In addition, 92 genes controlled four types of physiological and biochemical processes such as oxidative stress response (3), immune system process (55), apoptosis (4), and reorganization of the cytoskeleton and extracellular matrix (30). Further, the RT-qPCR results confirmed the accuracy of RNA-sequencing analysis. Our results showed the dynamic changes in global gene expression during tenderization and provided a series of candidate genes that contributed to tenderization in AJBW. This can help further studies on the genetics/molecular mechanisms associated with tenderization.

Reference assembly and gene expression analysis of Apostichopus japonicus larval development

The transcriptome of the holothurian Apostichopus japonicus was sequenced at four developmental stages-blastula, gastrula, auricularia, pentactula-on an Illumina sequencer. Based on our RNA-seq data and the paired-end reads from 16 libraries obtained by other researchers earlier, we have achieved the currently most complete transcriptome assembly for A. japonicus with the best basic statistical parameters. An analysis of the obtained transcriptome has revealed 174 differentially expressed transcription factors, as well as stage-specific transcription factors that are most promising for further study. In addition, a total of 1,174,999 high-quality single nucleotide polymorphisms have been identified, including 58,932 indels. A GO enrichment analysis of contigs containing polymorphic loci shows the predominance of GO terms associated with immune response. The data obtained by us provide an additional basis for a deeper study of the mechanisms of the planktotrophic-type development in holothurians and can be used in commercial sea cucumber breeding programs.

Analysis of microsatellites from transcriptome sequences of Phytophthora capsici and applications for population studies

Phytophthora capsici is a devastating oomycete that affects solanaceous, cucurbitaceous, fabaceous, and other crops in the United States (US) and worldwide. The release of the P. capsici genome allows for design of robust markers for genetic studies. We identified and characterized microsatellites in the P. capsici transcriptome. A subset of 50 microsatellites were assayed in a diverse set of P. capsici isolates and evaluated for polymorphism. Polymorphic microsatellites were confirmed by fragment analysis, and 12 were used for population characterization of 50 P. capsici isolates from different states, hosts, and mating types. Analysis of genetic relationship among isolates revealed significant geographic structure by state. Our findings highlight the usefulness of these 12 microsatellites to characterize the population structure of P. capsici and potential transferability to closely-related Phytophthora spp. since markers are located in coding regions. Our markers will facilitate genetic characterization and complement phenotypic studies of P. capsici populations, which may assist in deployment of disease management strategies.

Molecular mechanisms of an antimicrobial peptide piscidin (Lc-pis) in a parasitic protozoan, Cryptocaryon irritans

Background

Cryptocaryon irritans is an obligate parasitic ciliate protozoan that can infect various commercially important mariculture fish species and cause high lethality and economic loss. Current methods of controlling this parasite with chemicals or antibiotics are widely considered to be environmentally harmful. Piscidins with broad spectrum antibacterial, antifungal and antiviral activities were found to have potent activity against C. irritans. Little, however, has been understood about the killing mechanisms of piscidins in parasites.

Results

In total, 57.12, 50.44, 55.86 and 47.87 million raw reads were generated from untreated theront and trophont, and piscidin (Lc-pis) treated theront and trophont libraries, respectively. After de novo assembly, 966,609 unigenes were generated with an average length of 420 bp: among these, 618,629 unigenes showed identity with sequences in one or more databases, with some showing to be significantly manipulated by Lc-pis treatment. The species classification showed that more than 25.8% unigenes from trophonts were homologous to the large yellow croaker (Larimichthys crocea) and less than 3.8% unigenes from theronts were matched. The homologous unigenes demonstrated that the tissue from host could exist in trophonts and might be transported to parasite via vesicular transports. Our analysis showed that regulatory transcripts were involved in vesicular trafficking. Among transcripts induced by Lc-pis, most genes up-regulated in treated and untreated theronts were involved in cell migration and apoptosis related pathways. Few transcripts were found to be down-regulated in treated and untreated trophonts related to cell structure and migration after treatment.

Conclusions

This is the first transcriptome analysis of C. irritans exposed to Lc-pis, which enhanced the genomic resources and provided novel insights into molecular mechanisms of ciliates treated by cationic antimicrobial peptide. Our comprehensive transcriptome analysis can facilitate the identification of potential drug targets and vaccines candidates for controlling this devastating fish pathogen.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4565-5) contains supplementary material, which is available to authorized users.

Immune-related proteins detected through iTRAQ-based proteomics analysis of intestines from Apostichopus japonicus in response to tussah immunoreactive substances

Apostichopus japonicus is a species of sea cucumber that is extensively bred as a marine delicacy because of its high nutritive and medicinal value. Immunostimulants are usually used to enhance the immunity of sea cucumber against diseases, but the physiological function of immunostimulants is poorly understood. In this study, we fed A. japonicus individuals with a diet supplemented with different concentrations of tussah immunoreactive substances (TIS), and then subjected their intestines to iTRAQ-based proteomic analysis. A total of 51 differentially expressed proteins were detected in response to TIS, 13 proteins were upregulated, while 38 proteins were reduced. These proteins are involved in phagocytosis, tissue protection, cell apoptosis and energy metabolism. Among these 51 proteins, 7 proteins (GLO2, ACOX, CTTN, MARK, FADD, CSTA and CASP6) related to immunity with functional annotation in sea cucumber were further analyzed. In addition, the upregulated expression of 4 immune-related proteins (GLO2, ACOX, CTTN and MARK) was validated by qRT-PCR. The findings of this study gave further insight into the mechanism by which TIS might enhance the immunity of A. japonicus.

Differential gene expression in the intestine of sea cucumber (Apostichopus japonicus) under low and high salinity conditions

Sea cucumber, Apostichopus japonicus is an important species for aquaculture, and its behavior and physiology can change in response to changing salinity conditions. For this reason, it is important to understand the molecular responses of A. japonicus when exposed to ambient changes in salinity. In this study, RNA-Seq provided a general overview of the gene expression profiles in the intestine of A. japonicus exposed to high salinity (SD40), normal salinity (SD30) and low salinity (SD20) environments. Screening for differentially expressed genes (DEGs) using the NOISeq method identified 109, 100, and 89 DEGs based on a fold change of ≥2 and divergence probability ≥0.8 according to the comparisons of SD20 vs. SD30, SD20 vs.SD40, and SD30 vs. SD40, respectively. Gene ontology analysis showed that the terms "metabolic process" and "catalytic activity" comprised the most enriched DEGs. These fell into the categories of "biological process" and "molecular function". While "cell" and "cell part" had the most enriched DEGs in the category of "cellular component". With these DEGs mapping to 2119, 159, and 160 pathways in the Kyoto Encyclopedia of Genes and Genomes database. Of these 51, 2, and 57 pathways were significantly enriched, respectively. The osmosis-specific DEGs identified in this study of A. japonicus will be important targets for further studies to understand the biochemical mechanisms involved with the adaption of sea cucumbers to changes in salinity.

A novel TNFAIP8 gene mediates l-arginine metabolism in Apostichopus japonicus

Tumor necrosis factor (TNF)-α-induced protein 8 (TNFAIP8) family is a newly identified protein with vital roles in maintaining immune homeostasis. In the current study, we first cloned and characterized a TNFAIP8 gene from the invertebrate sea cucumber Apostichopus japonicus. The gene was designated as AjTNFAIP8. The full-length cDNA of AjTNFAIP8 was 1455 bp long and encoded a matured protein of 201 amino acid residues. Structural analysis indicated that AjTNFAIP8 had a death effector domain (DED)-like domain and composed of six α-helices. Multiple sequence alignment and phylogenetic analysis supported that AjTNFAIP8 is a new member of the TNFAIP8 family. Analysis of basal transcription in five tissues revealed the constitutive expression of AjTNFAIP8 in the detected tissues with highest expression in the respiratory tree and minimum expression in the tentacle. Vibrio splendidus infection and LPS stimulation could significantly downregulate the mRNA expression of AjTNFAIP8. More importantly, the transcription of pro-inflammatory molecule NOS and its production of NO content were significantly increased after AjTNFAIP8 silencing, with the suppression of agmatinase transcript and arginase activity. These results clearly indicated that AjTNFAIP8 is an essential negative regulator in innate immunity. Basic information for further exploration of the functional mechanisms of TNFAIP8 family in other marine invertebrate is provided.

Gene expression profiling during the embryo-to-larva transition in the giant red sea urchin Mesocentrotus franciscanus

In echinoderms, major morphological transitions during early development are attributed to different genetic interactions and changes in global expression patterns that shape the regulatory program for the specification of embryonic territories. In order more thoroughly to understand these biological and molecular processes, we examined the transcriptome structure and expression profiles during the embryo‐to‐larva transition of a keystone species, the giant red sea urchin Mesocentrotus franciscanus. Using a de novo assembly approach, we obtained 176,885 transcripts from which 60,439 (34%) had significant alignments to known proteins. From these transcripts, ~80% were functionally annotated allowing the identification of ~2,600 functional, structural, and regulatory genes involved in developmental process. Analysis of expression profiles between gastrula and pluteus stages of M. franciscanus revealed 791 differentially expressed genes with 251 GO overrepresented terms. For gastrula, up‐regulated GO terms were mainly linked to cell differentiation and signal transduction involved in cell cycle checkpoints. In the pluteus stage, major GO terms were associated with phosphoprotein phosphatase activity, muscle contraction, and olfactory behavior, among others. Our evolutionary comparative analysis revealed that several of these genes and functional pathways are highly conserved among echinoids, holothuroids, and ophiuroids.

Functional insights into the testis transcriptome of the edible sea urchin Loxechinus albus

The edible sea urchin Loxechinus albus (Molina, 1782) is a keystone species in the littoral benthic systems of the Pacific coast of South America. The international demand for high-quality gonads of this echinoderm has led to an extensive exploitation and decline of its natural populations. Consequently, a more thorough understanding of L. albus gonad development and gametogenesis could provide valuable resources for aquaculture applications, management, conservation and studies about the evolution of functional and structural pathways that underlie the reproductive toolkit of marine invertebrates. Using a high-throughput sequencing technology, we explored the male gonad transcriptome of this highly fecund sea urchin. Through a de novo assembly approach we obtained 42,530 transcripts of which 15,544 (36.6%) had significant alignments to known proteins in public databases. From these transcripts, approximately 73% were functionally annotated allowing the identification of several candidate genes that are likely to play a central role in developmental processes, nutrient reservoir activity, sexual reproduction, gamete generation, meiosis, sex differentiation, sperm motility, male courtship behavior and fertilization. Additionally, comparisons with the male gonad transcriptomes of other echinoderms revealed several conserved orthologous genes, suggesting that similar functional and structural pathways underlie the reproductive development in this group and other marine invertebrates.

Transcriptomic SNP discovery for custom genotyping arrays: impacts of sequence data, SNP calling method and genotyping technology on the probability of validation success

BACKGROUND

Single nucleotide polymorphism (SNP) discovery is an important goal of many studies. However, the number of 'putative' SNPs discovered from a sequence resource may not provide a reliable indication of the number that will successfully validate with a given genotyping technology. For this it may be necessary to account for factors such as the method used for SNP discovery and the type of sequence data from which it originates, suitability of the SNP flanking sequences for probe design, and genomic context. To explore the relative importance of these and other factors, we used Illumina sequencing to augment an existing Roche 454 transcriptome assembly for the Antarctic fur seal (Arctocephalus gazella). We then mapped the raw Illumina reads to the new hybrid transcriptome using BWA and BOWTIE2 before calling SNPs with GATK. The resulting markers were pooled with two existing sets of SNPs called from the original 454 assembly using NEWBLER and SWAP454. Finally, we explored the extent to which SNPs discovered using these four methods overlapped and predicted the corresponding validation outcomes for both Illumina Infinium iSelect HD and Affymetrix Axiom arrays.

RESULTS

Collating markers across all discovery methods resulted in a global list of 34,718 SNPs. However, concordance between the methods was surprisingly poor, with only 51.0 % of SNPs being discovered by more than one method and 13.5 % being called from both the 454 and Illumina datasets. Using a predictive modeling approach, we could also show that SNPs called from the Illumina data were on average more likely to successfully validate, as were SNPs called by more than one method. Above and beyond this pattern, predicted validation outcomes were also consistently better for Affymetrix Axiom arrays.

CONCLUSIONS

Our results suggest that focusing on SNPs called by more than one method could potentially improve validation outcomes. They also highlight possible differences between alternative genotyping technologies that could be explored in future studies of non-model organisms.

Long Non-Coding RNAs (lncRNAs) of Sea Cucumber: Large-Scale Prediction, Expression Profiling, Non-Coding Network Construction, and lncRNA-microRNA-Gene Interaction Analysis of lncRNAs in Apostichopus japonicus and Holothuria glaberrima During LPS Challenge and Radial Organ Complex Regeneration

Long non-coding RNA (lncRNA) structurally resembles mRNA but cannot be translated into protein. Although the systematic identification and characterization of lncRNAs have been increasingly reported in model species, information concerning non-model species is still lacking. Here, we report the first systematic identification and characterization of lncRNAs in two sea cucumber species: (1) Apostichopus japonicus during lipopolysaccharide (LPS) challenge and in heathy tissues and (2) Holothuria glaberrima during radial organ complex regeneration, using RNA-seq datasets and bioinformatics analysis. We identified A. japonicus and H. glaberrima lncRNAs that were differentially expressed during LPS challenge and radial organ complex regeneration, respectively. Notably, the predicted lncRNA-microRNA-gene trinities revealed that, in addition to targeting protein-coding transcripts, miRNAs might also target lncRNAs, thereby participating in a potential novel layer of regulatory interactions among non-coding RNA classes in echinoderms. Furthermore, the constructed coding-non-coding network implied the potential involvement of lncRNA-gene interactions during the regulation of several important genes (e.g., Toll-like receptor 1 [TLR1] and transglutaminase-1 [TGM1]) in response to LPS challenge and radial organ complex regeneration in sea cucumbers. Overall, this pioneer systematic identification, annotation, and characterization of lncRNAs in echinoderm pave the way for similar studies and future genetic, genomic, and evolutionary research in non-model species.

RNA sequencing analysis to capture the transcriptome landscape during skin ulceration syndrome progression in sea cucumber Apostichopus japonicus

Background

Sea cucumber Apostichopus japonicus is an important economic species in China, which is affected by various diseases; skin ulceration syndrome (SUS) is the most serious. In this study, we characterized the transcriptomes in A. japonicus challenged with Vibrio splendidus to elucidate the changes in gene expression throughout the three stages of SUS progression.

Results

RNA sequencing of 21 cDNA libraries from various tissues and developmental stages of SUS-affected A. japonicus yielded 553 million raw reads, of which 542 million high-quality reads were generated by deep-sequencing using the Illumina HiSeq™ 2000 platform. The reference transcriptome comprised a combination of the Illumina reads, 454 sequencing data and Sanger sequences obtained from the public database to generate 93,163 unigenes (average length, 1,052 bp; N50 = 1,575 bp); 33,860 were annotated. Transcriptome comparisons between healthy and SUS-affected A. japonicus revealed greater differences in gene expression profiles in the body walls (BW) than in the intestines (Int), respiratory trees (RT) and coelomocytes (C). Clustering of expression models revealed stable up-regulation as the main pattern occurring in the BW throughout the three stages of SUS progression. Significantly affected pathways were associated with signal transduction, immune system, cellular processes, development and metabolism. Ninety-two differentially expressed genes (DEGs) were divided into four functional categories: attachment/pathogen recognition (17), inflammatory reactions (38), oxidative stress response (7) and apoptosis (30). Using quantitative real-time PCR, twenty representative DEGs were selected to validate the sequencing results. The Pearson’s correlation coefficient (R) of the 20 DEGs ranged from 0.811 to 0.999, which confirmed the consistency and accuracy between these two approaches.

Conclusions

Dynamic changes in global gene expression occur during SUS progression in A. japonicus. Elucidation of these changes is important in clarifying the molecular mechanisms associated with the development of SUS in sea cucumber.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2810-3) contains supplementary material, which is available to authorized users.

De Novo Adult Transcriptomes of Two European Brittle Stars: Spotlight on Opsin-Based Photoreception

Next generation sequencing (NGS) technology allows to obtain a deeper and more complete view of transcriptomes. For non-model or emerging model marine organisms, NGS technologies offer a great opportunity for rapid access to genetic information. In this study, paired-end Illumina HiSeqTM technology has been employed to analyse transcriptomes from the arm tissues of two European brittle star species, Amphiura filiformis and Ophiopsila aranea. About 48 million Illumina reads were generated and 136,387 total unigenes were predicted from A. filiformis arm tissues. For O. aranea arm tissues, about 47 million reads were generated and 123,324 total unigenes were obtained. Twenty-four percent of the total unigenes from A. filiformis show significant matches with sequences present in reference online databases, whereas, for O. aranea, this percentage amounts to 23%. In both species, around 50% of the predicted annotated unigenes were significantly similar to transcripts from the purple sea urchin, the closest species to date that has undergone complete genome sequencing and annotation. GO, COG and KEGG analyses were performed on predicted brittle star unigenes. We focused our analyses on the phototransduction actors involved in light perception. Firstly, two new echinoderm opsins were identified in O. aranea: one rhabdomeric opsin (homologous to vertebrate melanopsin) and one RGR opsin. The RGR-opsin is supposed to be involved in retinal regeneration while the r-opsin is suspected to play a role in visual-like behaviour. Secondly, potential phototransduction actors were identified in both transcriptomes using the fly (rhabdomeric) and mammal (ciliary) classical phototransduction pathways as references. Finally, the sensitivity of O.aranea to monochromatic light was investigated to complement data available for A. filiformis. The presence of microlens-like structures at the surface of dorsal arm plate of O. aranea could potentially explain phototactic behaviour differences between the two species. The results confirm (i) the ability of these brittle stars to perceive light using opsin-based photoreception, (ii) suggest the co-occurrence of both rhabdomeric and ciliary photoreceptors, and (iii) emphasise the complexity of light perception in this echinoderm class.

Comparative transcriptome analysis of papilla and skin in the sea cucumber, Apostichopus japonicus

Papilla and skin are two important organs of the sea cucumber. Both tissues have ectodermic origin, but they are morphologically and functionally very different. In the present study, we performed comparative transcriptome analysis of the papilla and skin from the sea cucumber (Apostichopus japonicus) in order to identify and characterize gene expression profiles by using RNA-Seq technology. We generated 30.6 and 36.4 million clean reads from the papilla and skin and de novo assembled in 156,501 transcripts. The Gene Ontology (GO) analysis indicated that cell part, metabolic process and catalytic activity were the most abundant GO category in cell component, biological process and molecular funcation, respectively. Comparative transcriptome analysis between the papilla and skin allowed the identification of 1,059 differentially expressed genes, of which 739 genes were expressed at higher levels in papilla, while 320 were expressed at higher levels in skin. In addition, 236 differentially expressed unigenes were not annotated with any database, 160 of which were apparently expressed at higher levels in papilla, 76 were expressed at higher levels in skin. We identified a total of 288 papilla-specific genes, 171 skin-specific genes and 600 co-expressed genes. Also, 40 genes in papilla-specific were not annotated with any database, 2 in skin-specific. Development-related genes were also enriched, such as fibroblast growth factor, transforming growth factor-β, collagen-α2 and Integrin-α2, which may be related to the formation of the papilla and skin in sea cucumber. Further pathway analysis identified ten KEGG pathways that were differently enriched between the papilla and skin. The findings on expression profiles between two key organs of the sea cucumber should be valuable to reveal molecular mechanisms involved in the development of organs that are related but with morphological differences in the sea cucumber.

Construction of a High-Density Genetic Map and Quantitative Trait Locus Mapping in the Sea Cucumber Apostichopus japonicus

Genetic linkage maps are critical and indispensable tools in a wide range of genetic and genomic research. With the advancement of genotyping-by-sequencing (GBS) methods, the construction of a high-density and high-resolution linkage maps has become achievable in marine organisms lacking sufficient genomic resources, such as echinoderms. In this study, high-density, high-resolution genetic map was constructed for a sea cucumber species, Apostichopus japonicus, utilizing the 2b-restriction site-associated DNA (2b-RAD) method. A total of 7839 markers were anchored to the linkage map with the map coverage of 99.57%, to our knowledge, this is the highest marker density among echinoderm species. QTL mapping and association analysis consistently captured one growth-related QTL located in a 5 cM region of linkage group (LG) 5. An annotated candidate gene, retinoblastoma-binding protein 5 (RbBP5), which has been reported to be an important regulator of cell proliferation, was recognized in the QTL region. This linkage map represents a powerful tool for research involving both fine-scale QTL mapping and marker assisted selection (MAS), and will facilitate chromosome assignment and improve the whole-genome assembly of sea cucumber in the future.

De novo assembly and analysis of tissue-specific transcriptomes revealed the tissue-specific genes and profile of immunity from Strongylocentrotus intermedius

Strongylocentrotus intermedius is an important marine species in north China and Japan. Recent years, diseases are threating the sea urchin aquaculture industry seriously. To provide a genetic resource for S. intermedius as well as overview the immune-related genes of S. intermedius, we performed transcriptome sequencing of three cDNA libraries representing three tissues, coelomocytes, gut and peristomial membrane respectively. In total 138,421 contigs were assembled from all sequencing data. 96,764 contigs were annotated according to bioinformatics databases, including NT, nr, Swiss-Prot, KEGG, COG. 49,336 Contigs were annotated as CDS. In this study, we obtained 24,778 gene families from S. intermedius transcriptome. The gene expression analysis revealed that more genes were expressed in gut, more high expression level genes in coelomocytes when compared with other tissues. Specific expressed contigs in coelomocytes, gut, and peristomial membrane were 546, 1136, and 1012 respectively. Pathway analysis suggested 25, 17 and 36 potential specifically pathways may specific progressed in peristomial membrane, gut and coelomocytes respectively. Similarities and differences between S. intermedius and other echinoderms were analyzed. S. intermedius was more homology to Strongylocentrotus purpuratus than others sea urchin. Of 24,778 genes, 1074 genes are immune-related, immune genes were expressed with a higher level in coelomocytes than other tissues. Complement system may be the most important immune system in sea urchin. We also identified 2438 SSRs and 16,236 SNPs for S. intermedius. These results provide a transcriptome resource and foundation to study molecular mechanisms of sea urchin immune system.

Effects of dietary Bacillus cereus G19, B. cereus BC-01, and Paracoccus marcusii DB11 supplementation on the growth, immune response, and expression of immune-related genes in coelomocytes and intestine of the sea cucumber (Apostichopus japonicus Selenka)

Probiotics have positive effects on the nutrient digestibility and absorption, immune responses, and growth of aquatic animals, including the sea cucumber (Apostichopus japonicus Selenka). A 60-day feeding trial was conducted to evaluate the effects of Bacillus cereus G19, B. cereus BC-01 and Paracoccus marcusii DB11 supplementation on the growth, immune response, and expression level of four immune-related genes (Aj-p105, Aj-p50, Aj-rel, and Aj-lys) in coelomocytes and the intestine of juvenile sea cucumbers. One group was fed the basal diet (control group), while three other groups were fed the basal diet supplemented with B. cereus G19 (G19 group), B. cereus BC-01 (BC group), or P. marcusii DB11 (PM group). The growth rate of sea cucumbers fed diets with probiotics supplementation was significantly higher than that of the control group (P < 0.05). Sea cucumbers in the G19 and PM groups had a significantly greater phagocytic activity of coelomocytes compared to the control group (P < 0.05), while those in the G19 and BC groups had a greater respiratory burst activity (P < 0.05). The alkaline phosphatase (AKP) activity of coelomocytes in sea cucumbers fed diets with probiotics supplementation was significantly higher than the control group (P < 0.05). Comparatively, superoxide dismutase (SOD) activity of coelomocytes for sea cucumber in the PM group was significantly greater (P < 0.05). As for the immune-related genes, B. cereus G19 supplementation significantly increased the expression level of the Aj-rel gene in coelomocytes (P < 0.05), while B. cereus BC-01 supplementation significantly increased that of the Aj-p50 gene as compared to the control group (P < 0.05). In the intestine, the relative expression level of Aj-p105, Aj-p50, and Aj-lys genes in the PM group was significantly higher than that in the control group (P < 0.05). These results suggested that B. cereus G19 and B. cereus BC-01 supplementation could improve the growth performance and the immune response in coelomocytes, while P. marcusii DB11 supplementation could have a positive effect on the growth performance and immune response in coelomocytes and the intestine of sea cucumbers.

De novo transcriptome of the European brittle star Amphiura filiformis pluteus larvae

BACKGROUND

In non-classical model species, Next Generation Sequencing increases the ability to analyze the expression of transcripts/genes. In this study, paired-end Illumina HiSeq sequencing technology has been employed to describe a larval transcriptome generated from 64 h post-fertilization pluteus larvae of the brittle star Amphiura filiformis. We focused our analysis on the detection of actors involved in the opsin based light perception, respectively the opsins and the phototransduction actors.

METHODS & RESULTS

In this research, about 47 million high quality reads were generated and 86,572 total unigenes were predicted after de novo assembly. Of all the larval unigenes, 18% show significant matches with reference online databases. 46% of annotated larval unigenes were significantly similar to transcripts from the purple sea urchin. COG, GO and KEGG analyses were performed on predicted unigenes. Regarding the opsin-based photoreception process, even if possible actors of ciliary and rhabdomeric phototransduction cascades were detected, no ciliary or rhabdomeric opsin was identified in these larvae. Additionally, partial non-visual RGR (retinal G protein coupled receptor) opsin mRNAs were identified,possibly indicating the presence of visual cycle reaction in early pluteus larvae. The eye morphogene Pax 6 was also identified in the pluteus transcriptome.

CONCLUSIONS

Contrary to sea-urchin larvae, brittle star larvae appear to be characterized by an absence of visual-like opsins. These RNA-seq data also provide a useful resource for the echinoderm research community and researchers with an interest in larval biology.

Functional marker detection and analysis on a comprehensive transcriptome of large yellow croaker by next generation sequencing

Large yellow croaker (Larimichthys crocea) is an important economic fish in China and Eastern Asia. Because of the exhaustive fishing and overdense aquaculture, the wild population and the mariculture of the species are facing serious challenges on germplasm degeneration and susceptibility to infectious disease agents. However, a comprehensive transcriptome from multi-tissues of the species has not been reported and functional molecular markers have not yet been detected and analyzed. In this work, we applied RNA-seq with the Illumina Hiseq2000 platform for a multi-tissue sample of large yellow croaker and assembled the transcriptome into 88,103 transcripts. Of them, 52,782 transcripts have been successfully annotated by nt/nr, InterPro, GO and KEGG database. Comparing with public fish proteins, we have found that 34,576 protein coding transcripts are shared in large yellow croaker with zebrafish, medaka, pufferfish, and stickleback. For functional markers, we have discovered 1,276 polymorphic SSRs and 261, 000 SNPs. The functional impact analysis of SNPs showed that the majority (~75%) of small variants cause synonymous mutations in proteins, followed by variations in 3' UTR region. The functional enrichment analysis illuminated that transcripts involved in DNA bindings, enzyme activities, and signal pathways prominently exhibit less single-nucleotide variants but genes for the constituent of the muscular tissue, the cytoskeleton, and the immunity system contain more frequent SNP mutations, which may reflect the structural and functional selections of the translated proteins. This is the first work for the high-throughput detection and analysis of functional polymorphic SSR and SNP markers in a comprehensive transcriptome of large yellow croaker. Our study provides valuable transcript sequence and functional marker resources for the quantitative trait locus (QTL) identification and molecular selection of the species in the research community.

Transcriptomic analysis of the underground renewal buds during dormancy transition and release in 'Hangbaishao' peony (Paeonia lactiflora)

Paeonia lactiflora is one of the most famous species of herbaceous peonies with gorgeous flowers. Bud dormancy is a crucial developmental process that allows P. lactiflora to survive unfavorable environmental conditions. However, little information is available on the molecular mechanism of the bud dormancy in P. lactiflora. We performed de novo transcriptome sequencing using the Illumina RNA sequencing platform for the underground renewal buds of P. lactiflora 'Hangbaishao' to study the molecular mechanism underlying its bud dormancy transition (the period from endodormancy to ecodormancy) and release (the period from ecodormancy to bud elongation and sprouting). Approximately 300 million high-quality clean reads were generated and assembled into 207,827 (mean length = 828 bp) and 51,481 (mean length = 1250 bp) unigenes using two assembly methods named "Trinity" and "Trinity+PRICE", respectively. Based on the data obtained by the latter method, 32,316 unigenes were annotated by BLAST against various databases. Approximately 1,251 putative transcription factors were obtained, of which the largest number of unique transcripts belonged to the basic helix-loop-helix protein (bHLH) transcription factor family, and five of the top ten highly expressed transcripts were annotated as dehydrin (DHN). A total of 17,705 simple sequence repeat (SSR) motifs distributed in 13,797 sequences were obtained. The budbreak morphology, levels of indole-3-acetic acid (IAA) and abscisic acid (ABA), and activities of guaiacol peroxidase (POD) and catalase (CAT) were observed. The expression of 20 interested unigenes, which annotated as DHN, heat shock protein (HSP), histone, late elongated hypocotyl (LHY), and phytochrome (PHY), and so on, were also analyzed. These studies were based on morphological, physiological, biochemical, and molecular levels and provide comprehensive insight into the mechanism of dormancy transition and release in P. lactiflora. Transcriptome dataset can be highly valuable for future investigation on gene expression networks in P. lactiflora as well as research on dormancy in other non-model perennial horticultural crops of commercial significance.

De novo transcriptome assembly and the identification of gene-associated single-nucleotide polymorphism markers in Asian and American ginseng roots

We performed de novo transcriptome sequencing for Panax ginseng and Panax quinquefolius accessions using the 454 GS FLX Titanium System and discovered annotation-based genome-wide single-nucleotide polymorphism (SNPs) using next-generation ginseng transcriptome data without reference genome sequence. The comprehensive transcriptome characterization with the mature roots of four ginseng accessions generated 297,170 reads for 'Cheonryang' cultivar, 305,673 reads for 'Yunpoong' cultivar, 311,861 reads for the G03080 breeding line, and 308,313 reads for P. quinquefolius. In transcriptome assembly, the lengths of the sample read were 156.42 Mb for 'Cheonryang', 161.95 Mb for 'Yunpoong', 165.07 Mb for G03080 breeding line, and 166.48 Mb for P. quinquefolius. A total of 97 primer pairs were designed with the homozygous SNP presented in all four accessions. SNP genotyping using high-resolution melting (HRM) analysis was performed to validate the putative SNP markers of 97 primer pairs. Out of the 73 primer pairs, 73 primer pairs amplified the target sequence and 34 primer pairs showed polymorphic melting curves in samples from 11 P. ginseng cultivars and one P. quinquefolius accession. Among the 34 polymorphic HRM-SNP primers, four primers were useful to distinguish ginseng cultivars. In the present study, we demonstrated that de novo transcriptome assembly and mapping analyses are useful in providing four HRM-SNP primer pairs that reliably show a high degree of polymorphism among ginseng cultivars.

Comparative transcriptome analysis of two oysters, Crassostrea gigas and Crassostrea hongkongensis provides insights into adaptation to hypo-osmotic conditions

Environmental salinity creates a key barrier to limit the distribution of most aquatic organisms. Adaptation to osmotic fluctuation is believed to be a factor facilitating species diversification. Adaptive evolution often involves beneficial mutations at more than one locus. Bivalves hold great interest, with numerous species living in waters, as osmoconformers, who maintain the osmotic pressure balance mostly by free amino acids. In this study, 107,076,589 reads from two groups of Crassostrea hongkongensis were produced and the assembled into 130,629 contigs. Transcripts putatively involved in stress-response, innate immunity and cell processes were identified according to Gene ontology and KEGG pathway analyses. Comparing with the transcriptome of C. gigas to characterize the diversity of transcripts between species with osmotic divergence, we identified 182,806 high-quality single nucleotide polymorphisms (SNPs) for C. hongkongensis, and 196,779 SNPs for C. gigas. Comparison of 11,602 pairs of putative orthologs allowed for identification of 14 protein-coding genes that experienced strong positive selection (Ka/Ks>1). In addition, 45 genes that may show signs of moderate positive selection (1 ≥ Ka/Ks>0.5) were also identified. Based on Ks ratios and divergence time between the two species published previously, we estimated a neutral transcriptome-wide substitution mutation rate of 1.39 × 10(-9) per site per year. Several genes were differentially expressed across the control and treated groups of each species. This is the first time to sequence the transcriptome of C. hongkongensis and provide the most comprehensive transcriptomic resource available for it. The increasing amount of transcriptome data on Crassostrea provides an excellent resource for phylogenetic analysis. A large number of SNPs identified in this work are expected to provide valuable resources for future marker and genotyping assay development. The analysis of natural selection provides an innovative view on the adaptation within species and sets the basis for future genetic and evolutionary studies.

Expression analysis of immune related genes identified from the coelomocytes of sea cucumber (Apostichopus japonicus) in response to LPS challenge

The sea cucumber (Apostichopus japonicus) occupies a basal position during the evolution of deuterostomes and is also an important aquaculture species. In order to identify more immune effectors, transcriptome sequencing of A. japonicus coelomocytes in response to lipopolysaccharide (LPS) challenge was performed using the Illumina HiSeq™ 2000 platform. One hundred and seven differentially expressed genes were selected and divided into four functional categories including pathogen recognition (25 genes), reorganization of cytoskeleton (27 genes), inflammation (41 genes) and apoptosis (14 genes). They were analyzed to elucidate the mechanisms of host-pathogen interactions and downstream signaling transduction. Quantitative real-time polymerase chain reactions (qRT-PCRs) of 10 representative genes validated the accuracy and reliability of RNA sequencing results with the correlation coefficients from 0.88 to 0.98 and p-value <0.05. Expression analysis of immune-related genes after LPS challenge will be useful in understanding the immune response mechanisms of A. japonicus against pathogen invasion and developing strategies for resistant markers selection.