Fucoxanthin Alleviates Dextran Sulfate Sodium-Induced Colitis and Gut Microbiota Dysbiosis in Mice.

The purpose of this study was to evaluate the preventive role and underlying mechanisms of fucoxanthin (Fx) on dextran sulfate sodium (DSS)-induced colitis in mice. The present data demonstrated that oral administration of Fx (50 and 200 mg/kg body weight/day) for 36 days significantly alleviated the severity of colitis in DSS-treated mice, as evidenced by attenuating body weight loss, bloody stool, diarrhea, shortened colon length, colonic epithelium distortion, a thin mucus layer, goblet cell depletion, damaged crypts, and extensive infiltration of inflammatory cells in the colonic mucosa. Additionally, Fx notably relieved DSS-induced intestinal epithelial barrier dysfunction via maintaining the tight junction function and preventing excessive apoptosis of colonic epithelial cells. Moreover, Fx effectively diminished colonic inflammation and oxidative stress in DSS-treated mice, and its mechanisms might be due to blunting the activation of NF-κB and NLRP3 inflammasome signaling pathways. Furthermore, Fx also modulates DSS-induced gut microbiota dysbiosis via recovering the richness and diversity of gut microbiota and reshaping the structure of gut microbiota, such as increasing the Firmicutes and Bacteroidota (F/B) ratio and elevating the relative abundance of some potential beneficial bacteria, including Lactobacillaceae and Lachnospiraceae. Overall, Fx might be developed as a promising functional ingredient to prevent colitis and maintain intestinal homeostasis.

Preparation of Multifunctional Seaweed Polysaccharides Derivatives Composite Hydrogel to Protect Ultraviolet B-Induced Photoaging In Vitro and In Vivo.

Seaweed polysaccharides can be used for protective skin photoaging which is caused by long-term exposure to ultraviolet B (UVB). In this study, a multifunctional composite hydrogel (FACP5) is prepared using sulfated galactofucan polysaccharides, alginate oligosaccharides as active ingredients, and polyacrylonitrile modified κ-Carrageenan as substrate. The properties of FACP5 show that it has good water retention, spreadability, and adhesion. The antiphotoaging activity is evaluated in vitro and in vivo. In vitro experiments demonstrate that the components of FACP5 exhibit good biocompatibility, antioxidant, and anti-tyrosinase activities, and could reduce the cell death rate induced by UVB. In vivo experiments demonstrate that, compared with the mice skin in model group, the skin water content treated with FACP5 increases by 29.80%; the thicknesses of epidermis and dermis decrease by 53.56% and 43.98%, respectively; the activities of catalase and superoxide dismutase increase by 1.59 and 0.72 times, respectively; the contents of interleukin-6 and tumor necrosis factor-α decrease by 19.21% and 17.85%, respectively; hydroxyproline content increases by 32.42%; the expression level of matrix metalloproteinase-3 downregulates by 42.80%. These results indicate that FACP5 has skin barrier repairing, antioxidant, anti-inflammatory, and inhibiting collagen degradation activies, FACP5 can be used as a skin protection remedy for photoaging.

Isolation and characterization of glutathione S-transferase genes and their transcripts in Saccharina japonica (Laminariales, Phaeophyceae) during development and under abiotic stress.

BACKGROUND: Glutathione S-transferase (GST) is a crucial enzyme for metabolism, detoxification, and stress resistance in organisms. Many GSTs have been identified in seaweeds, but the isolation and functional analysis of GSTs in Saccharina japonica have not been completed. RESULT: In this study, a total of 32 SjGST genes, localized on 10 scaffolds and 6 contigs, were identified and categorized into three groups. Most of these SjGSTs were presumed to be distributed in the cytoplasm. Tandem duplication had a significant influence on the expansion of the SjGST gene family. Functional analysis of cis-acting elements in the promoter regions demonstrated that SjGSTs enhance the stress resistance of the kelp. Quantitative real-time PCR tests confirmed that SjGSTs positively influence S. japonica sporophytes under stress from low salinity, drought, and high temperature. Recombinant yeast tests further affirmed the role of SjGSTs in stress resistance; SjGSTs improved the growth rate of recombinant yeast under 1.5 M NaCl or 8 mM H2O2. Analysis of biochemical parameters indicated that the optimum temperatures for SjGST20 and SjGST22 were 20 °C, and the optimum pH values were 7.0 and 8.0 for SjGST20 and SjGST22, respectively. The Km values for the substrate 1-chloro-2,4-dinitrobenzene (CDNB) were 2.706 mM and 0.674 mM and were 6.146 mM and 3.559 mM for the substrate glutathione (GSH) for SjGST20 and SjGST22, respectively. CONCLUSION: SjGSTs are important stress resistant genes in S. japonica. This research results will enhance our understanding the function of GSTs in brown seaweeds, and explained its functional roles in stress resistance in marine environments.

Characterization of Chlorophyll Fluorescence and Antioxidant Defense Parameters of Two Gracilariopsis lemaneiformis Strains under Different Temperatures.

In this study, two Gracilariopsis lemaneiformis strains-the wild type and a green-pigmented mutant-were cultured at three temperatures (8, 20, and 30 °C) for 7 days to explore their temperature tolerance using photosynthetic performance and antioxidant defense parameters. When the two strains of G. lemaneiformis were separately cultured at 30 °C, the fast chlorophyll fluorescence intensity of the wild type decreased, whereas the green mutant showed no significant change. The decrease in the performance index on absorption basis value under heat stress was lower in the green mutant than in the wild type. In addition, the green mutant had stronger antioxidant activity at 30 °C. Furthermore, a greater decrease in the values of maximum photochemical quantum yield and performance index on an absorption basis in the green mutant indicated that it had a greater degree of inhibition of photosynthetic performance under low temperatures. However, the green mutant produced less reactive oxygen species under low temperatures, suggesting that the antioxidant potential of the green mutant might be higher. In conclusion, the green mutant exhibited heat tolerance and could recover from low-temperature damage; therefore, it has the potential for large-scale cultivation.

Isolation and functional verification of an aspartate aminotransferase gene from Neoporphyra haitanensis.

BACKGROUND: Neoporphyra haitanensis is a commercial laver species in China. Aspartic acid is an important flavor amino acid, and aspartate aminotransferase (AAT) is a crucial enzyme in its biosynthesis. In this study, we cloned one AAT gene (NhAAT) from the red alga N. haitanensis and investigated its sequence structure, transcriptional expression and enzymatic characteristics. The purpose of our research is to obtain a functional AAT responsible for the biosynthesis of aspartic acid from red seaweeds, which has the potential to influence the flavor of N. haitanensis. RESULTS: Sequence analysis showed that NhAAT contains a conserved domain of Aminotran_1_2, which belongs to the transaminase superfamily. The secondary structure of NhAAT is dominated by α-helix. The results of enzymatic characterization illustrated that the NhAAT has highest catalytic activity at 45 °C and pH 7.5 in both forward and reverse reactions. The calculated Km values of NhAAT was 5.67 and 6.16 mM for L-glutamic acid and L-aspartic acid, respectively. Quantitative analysis showed that the NhAAT expression of N. haitanensis collected in late harvest (Dec) was 4.5 times that of N. haitanensis collected in early harvest (Oct), while the aspartic acid content of N. haitanensis collected in late harvest (Dec) was 1.2 times that of N. haitanensis collected in early harvest (Oct). CONCLUSION: The results of enzyme kinetics indicated that NhAAT prefers to catalyze the reaction in the direction of aspartic acid production. Moreover, the trend of NhAAT expression level was consistent with that of aspartic acid content in N. haitanensis in different harvest periods. Our research is helpful to understand the accumulation and regulation of amino acids in N. haitanensis in different habitats and the taste difference of N. haitanensis in different harvest periods.

Novel Chitin Deacetylase from Thalassiosira weissflogii Highlights the Potential for Chitin Derivative Production.

ß-Chitin is an important carbon fixation product of diatoms, and is the most abundant nitrogen-containing polysaccharide in the ocean. It has potential for widespread application, but the characterization of chitin-related enzymes from ß-chitin producers has rarely been reported. In this study, a chitin deacetylase (TwCDA) was retrieved from the Marine Microbial Eukaryote Transcriptome Sequencing Project (MMETSP) database and was heterologously expressed in vitro for functional analysis. The results showed that both the full-length sequence (TwCDA) and the N-terminal truncated sequence (TwCDA-S) had chitin deacetylase and chitinolytic activities after expression in Escherichia coli. High-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) indicated that TwCDA and TwCDA-S could catalyze the deacetylation of oligosaccharide (GlcNAc)5. TwCDA had higher deacetylase activity, and also catalyzed the deacetylation of the ß-chitin polymer. A dinitrosalicylic acid (DNS) assay showed that TwCDA-S had high chitinolytic activity for (GlcNAc)5, and the optimal reaction temperature was 35 °C. Liquid chromatography combined with time-of-flight mass spectrometry (LC-coTOF-MS) detected the formation of a N-acetylglucosamine monomer (C8H15NO6) in the reaction mixture. Altogether, we isolated a chitin deacetylase from a marine diatom, which can catalyze the deacetylation and degradation of chitin and chitin oligosaccharides. The relevant results lay a foundation for the internal regulation mechanism of chitin metabolism in diatoms and provide a candidate enzyme for the green industrial preparation of chitosan and chitin oligosaccharides.

Characterization of a Marine Diatom Chitin Synthase Using a Combination of Meta-Omics, Genomics, and Heterologous Expression Approaches.

ß-Chitin has important ecological and physiological roles and potential for widespread applications, but the characterization of chitin-related enzymes from ß-chitin producers was rarely reported. Querying against the Tara Oceans Gene Atlas, 4,939 chitin-related unique sequences from 12 Pfam accessions were found in Bacillariophyta metatranscriptomes. Putative chitin synthase (CHS) sequences are decreasingly present in Crustacea (39%), Stramenopiles (16%) and Insecta (14%) from the Marine Atlas of Tara Oceans Unigenes version 1 Metatranscriptomes (MATOUv1+T) database. A CHS gene from the model diatom Thalassiosira pseudonana (Thaps3_J4413, designated TpCHS1) was identified. Homology analysis of TpCHS1 in Marine Microbial Eukaryote Transcriptome Sequencing Project (MMETSP), PhycoCosm, and the PLAZA diatom omics data set showed that Mediophyceae and Thalassionemales species were potential new ß-chitin producers besides Thalassiosirales. TpCHS1 was overexpressed in Saccharomyces cerevisiae and Phaeodactylum tricornutum. In transgenic P. tricornutum lines, TpCHS1-eGFP localizes to the Golgi apparatus and plasma membrane and predominantly accumulates in the cleavage furrow during cell division. Enhanced TpCHS1 expression could induce abnormal cell morphology and reduce growth rates in P. tricornutum, which might be ascribed to the inhibition of the G2/M phase. S. cerevisiae was proved to be a better system for expressing large amounts of active TpCHS1, which effectively incorporates UDP-N-acetylglucosamine in radiometric in vitro assays. Our study expands the knowledge on chitin synthase taxonomic distribution in marine eukaryotic microbes, and is the first to collectively characterize an active marine diatom CHS which may play an important role during cell division. IMPORTANCE As the most abundant biopolymer in the oceans, the significance of chitin and its biosynthesis is rarely demonstrated in diatoms, which are the main contributors to the primary productivity of the oceans, ascribed to their huge biomass and efficient photosynthesis. We retrieved genes involved in chitin-based metabolism against the Tara Oceans Gene Atlas to expand our knowledge about their diversity and distribution in the marine environment. Potential new producers of chitin were found from the analysis of various algal transcriptome and genome databases. Heterologous expression confirms that Thalassiosira pseudonana contains an active chitin synthase (CHS) which may play an important role in the cell division process of diatoms. This study provides new insight into CHS geographic and taxonomic distribution in marine eukaryotic microbes, as well as into a new CHS functioning in the biosynthesis of ß-chitin in diatoms.

Isolation, identification, and biochemical characterization of a novel bifunctional phosphomannomutase/phosphoglucomutase from the metagenome of the brown alga Laminaria digitata.

Macroalgae host diverse epiphytic bacterial communities with potential symbiotic roles including important roles influencing morphogenesis and growth of the host, nutrient exchange, and protection of the host from pathogens. Macroalgal cell wall structures, exudates, and intra-cellular environments possess numerous complex and valuable carbohydrates such as cellulose, hemi-cellulose, mannans, alginates, fucoidans, and laminarin. Bacterial colonizers of macroalgae are important carbon cyclers, acquiring nutrition from living macroalgae and also from decaying macroalgae. Seaweed epiphytic communities are a rich source of diverse carbohydrate-active enzymes which may have useful applications in industrial bioprocessing. With this in mind, we constructed a large insert fosmid clone library from the metagenome of Laminaria digitata (Ochrophyta) in which decay was induced. Subsequent sequencing of a fosmid clone insert revealed the presence of a gene encoding a bifunctional phosphomannomutase/phosphoglucomutase (PMM/PGM) enzyme 10L6AlgC, closely related to a protein from the halophilic marine bacterium, Cobetia sp. 10L6AlgC was subsequently heterologously expressed in Escherichia coli and biochemically characterized. The enzyme was found to possess both PMM and PGM activity, which had temperature and pH optima of 45°C and 8.0, respectively; for both activities. The PMM activity had a K m of 2.229 mM and V max of 29.35 mM min-1 mg-1, while the PGM activity had a K m of 0.5314 mM and a V max of 644.7 mM min-1 mg-1. Overall characterization of the enzyme including the above parameters as well as the influence of various divalent cations on these activities revealed that 10L6AlgC has a unique biochemical profile when compared to previously characterized PMM/PGM bifunctional enzymes. Thus 10L6AlgC may find utility in enzyme-based production of biochemicals with different potential industrial applications, in which other bacterial PMM/PGMs have previously been used such as in the production of low-calorie sweeteners in the food industry.

Organellar genome comparisons of Sargassum polycystum and S. plagiophyllum (Fucales, Phaeophyceae) with other Sargassum species.

BACKGROUND: Sargassum polycystum C. Agardh and Sargassum plagiophyllum C. Agardh are inhabitants of tropical coastal areas, their populations are negatively influenced by global warming and marine environment changes. The mitochondrial and chloroplast genomes of these species have not been sequenced. RESULTS: The mitochondrial genomes of S. polycystum and S. plagiophyllum were 34,825 bp and 34,862 bp, respectively, and their corresponding chloroplast genomes were 124,493 bp and 124,536 bp, respectively. The mitochondrial and chloroplast genomes of these species share conserved synteny, sequence regions and gene number when compared with the organellar genomes of other Sargassum species. Based on sequence analysis of 35 protein-coding genes, we deduced that S. polycystum and S. plagiophyllum were closely related with S. ilicifolium; these species diverged approximately 0.3 million years ago (Ma; 0.1-0.53 Ma) during the Pleistocene period (0.01-2.59 Ma). Rates of synonymous and non-synonymous substitutions in the mitochondrial genome of the Sargassum genus were 3 times higher than those in the chloroplast genome. In the mitochondrial genome, rpl5, rpl31 and rps11 had the highest synonymous substitution rates. In the chloroplast genome, psaE, rpl14 and rpl27 had the highest synonymous substitution rates. CONCLUSIONS: Phylogenetic analysis confirms the close relationship between the two sequenced species and S. ilicifolium. Both synonymous and non-synonymous substitution rates show significant divergence between the group of mitochondrial genomes versus the group of chloroplast genomes. The deciphering of complete mitochondrial and chloroplast genomes is significant as it advances our understanding of the evolutionary and phylogenetic relationships between species of brown seaweeds.

Prediction of the dynamic distribution for Eucheuma denticulatum (Rhodophyta, Solieriaceae) under climate change in the Indo-Pacific Ocean.

Eucheuma is one of the most important commercial red seaweeds in Southeast Asia, and plays an important role in the global seaweed aquaculture. It is expected to exhibit great responses to ocean warming. Here, we used maximum entropy species distribution models (SDMs) to estimate the suitable habitat of Eucheuma denticulatum under present conditions, and to predict the future range dynamics under the four representative concentration pathway (RCP) scenarios. The best marine environmental factors for E. denticulatum distribution modeling were distance to shore, sea surface temperature and currents velocity. Our results showed that E. denticulatum' distributions would contract in the Central Indo-Pacific Ocean, especially the regions of the Sunda Shelf, while expanding poleward along the south coast of Australia in 2100. Our study provided important knowledge for the prediction of the tropical seaweed distribution, conservation and sustainable developments of E. denticulatum in the future.

The organellar genomes of Silvetia siliquosa (Fucales, Phaeophyceae) and comparative analyses of the brown algae.

The brown alga Silvetia siliquosa (Tseng et Chang) Serrão, Cho, Boo & Brawly is endemic to the Yellow-Bohai Sea and southwestern Korea. It is increasingly endangered due to habitat loss and excessive collection. Here, we sequenced the mitochondrial (mt) and chloroplast (cp) genomes of S. siliquosa. De novo assembly showed that the mt-genome was 36,036 bp in length, including 38 protein-coding genes (PCGs), 26 tRNAs, and 3 rRNAs, and the cp-genome was 124,991 bp in length, containing 139 PCGs, 28 tRNAs, and 6 rRNAs. Gene composition, gene number, and gene order of the mt-genome and cp-genome were very similar to those of other species in Fucales. Phylogenetic analysis revealed a close genetic relationship between S. siliquosa and F. vesiculosus, which diverged approximately 8 Mya (5.7-11.0 Mya), corresponding to the Late Miocene (5.3-11.6 Ma). The synonymous substitution rate of mitochondrial genes of phaeophycean species was 1.4 times higher than that of chloroplast genes, but the cp-genomes were more structurally variable than the mt-genomes, with numerous gene losses and rearrangements among the different orders in Phaeophyceae. This study reports the mt- and cp-genomes of the endangered S. siliquosa and improves our understanding of its phylogenetic position in Phaeophyceae and of organellar genomic evolution in brown algae.

The Cell Wall Polysaccharides Biosynthesis in Seaweeds: A Molecular Perspective.

Cell wall polysaccharides (CWPS) of seaweeds play crucial roles in mechanical shear resistance, cell-cell adhesion and the interactions with changeable marine environments. They have diverse applications in food, cosmetics, agriculture, pharmaceuticals and therapeutics. The recent boost of multi-omics sequence analysis has rapidly progressed the mining of presumed genes encoding enzymes involved in CWPS biosynthesis pathways. In this review, we summarize the biosynthetic pathways of alginate, fucoidan, agar, carrageenan and ulvan in seaweeds referred to the literatures on published genomes and biochemical characterization of encoded enzymes. Some transcriptomic data were briefly reported to discuss the correlation between gene expression levels and CWPS contents. Mannuronan C-5 epimerase (MC5E) and carbohydrate sulfotransferase (CST) are crucial enzymes for alginate and sulfated CWPS, respectively. Nonetheless, most CWPS-relevant genes were merely investigated by gene mining and phylogenetic analysis. We offer an integrative view of CWPS biosynthesis from a molecular perspective and discuss about the underlying regulation mechanism. However, a clear understanding of the relationship between chemical structure and bioactivities of CWPS is limited, and reverse genetic manipulation and effective gene editing tools need to be developed in future.

Glutamate Dehydrogenase Functions in Glutamic Acid Metabolism and Stress Resistance in Pyropia haitanensis.

Pyropia haitanensis is an important laver species in China. Its quality traits are closely related to the content of glutamic acid. Glutamate dehydrogenase (GDH) is a crucial enzyme in the glutamic acid metabolism. In this study, two GDH genes from P. haitanensis, PhGDH1 and PhGDH2, were cloned and successfully expressed in Escherichia coli. The in vitro enzyme activity assay demonstrated that the catalytic activity of PhGDHs is mainly in the direction of ammonium assimilation. The measured Km values of PhGDH1 for NADH, (NH4)2SO4, and α-oxoglutarate were 0.12, 4.99, and 0.16 mM, respectively, while the corresponding Km values of PhGDH2 were 0.02, 3.98, and 0.104 mM, respectively. Site-directed mutagenesis results showed that Gly193 and Thr361 were important catalytic residues for PhGDH2. Moreover, expression levels of both PhGDHs were significantly increased under abiotic stresses. These results suggest that PhGDHs can convert α-oxoglutarate to glutamic acid, and enhance the flavor and stress resistance of P. haitanensis.

Genome-Wide Mapping of Cytosine Methylation Revealed Dynamic DNA Methylation Patterns Associated with Sporophyte Development of Saccharina japonica.

Cytosine methylation plays vital roles in regulating gene expression and plant development. However, the function of DNA methylation in the development of macroalgae remains unclear. Through the genome-wide bisulfite sequencing of cytosine methylation in holdfast, stipe and blade, we obtained the complete 5-mC methylation landscape of Saccharina japonica sporophyte. Our results revealed that the total DNA methylation level of sporophyte was less than 0.9%, and the content of CHH contexts was dominant. Moreover, the distribution of CHH methylation within the genes exhibited exon-enriched characteristics. Profiling of DNA methylation in three parts revealed the diverse methylation pattern of sporophyte development. These pivotal DMRs were involved in cell motility, cell cycle and cell wall/membrane biogenesis. In comparison with stipe and blade, hypermethylation of mannuronate C5-epimerase in holdfast decreased the transcript abundance, which affected the synthesis of alginate, the key component of cell walls. Additionally, 5-mC modification participated in the regulation of blade and holdfast development by the glutamate content respectively via glutamine synthetase and amidophosphoribosyl transferase, which may act as the epigenetic regulation signal. Overall, our study revealed the global methylation characteristics of the well-defined holdfast, stipe and blade, and provided evidence for epigenetic regulation of sporophyte development in brown macroalgae.

Molecular Mechanism of Anti-Inflammatory Activities of a Novel Sulfated Galactofucan from Saccharina japonica.

Seaweed of Saccharina japonica is the most abundantly cultured brown seaweed in the world, and has been consumed in the food industry due to its nutrition and the unique properties of its polysaccharides. In this study, fucoidan (LJNF3), purified from S. japonica, was found to be a novel sulfated galactofucan, with the monosaccharide of only fucose and galactose in a ratio of 79.22:20.78, and with an 11.36% content of sulfate groups. NMR spectroscopy showed that LJNF3 consists of (1→3)-α-l-fucopyranosyl-4-SO3 residues and (1→6)-ß-d-galactopyranose units. The molecular mechanism of the anti-inflammatory effect in RAW264.7 demonstrated that LJNF3 reduced the production of nitric oxide (NO), and down-regulated the expression of MAPK (including p38, ENK and JNK) and NF-κB (including p65 and IKKα/IKKß) signaling pathways. In a zebrafish experiment assay, LJNF3 showed a significantly protective effect, by reducing the cell death rate, inhibiting NO to 59.43%, and decreasing about 40% of reactive oxygen species. This study indicated that LJNF3, which only consisted of fucose and galactose, had the potential to be developed in the biomedical, food and cosmetic industries.

Full-Length Transcriptome of Thalassiosira weissflogii as a Reference Resource and Mining of Chitin-Related Genes.

ß-Chitin produced by diatoms is expected to have significant economic and ecological value due to its structure, which consists of parallel chains of chitin, its properties and the high abundance of diatoms. Nevertheless, few studies have functionally characterised chitin-related genes in diatoms owing to the lack of omics-based information. In this study, we first compared the chitin content of three representative Thalassiosira species. Cell wall glycosidic linkage analysis and chitin/chitosan staining assays showed that Thalassiosira weissflogii was an appropriate candidate chitin producer. A full-length (FL) transcriptome of T. weissflogii was obtained via PacBio sequencing. In total, the FL transcriptome comprised 23,362 annotated unigenes, 710 long non-coding RNAs (lncRNAs), 363 transcription factors (TFs), 3113 alternative splicing (AS) events and 3295 simple sequence repeats (SSRs). More specifically, 234 genes related to chitin metabolism were identified and the complete biosynthetic pathways of chitin and chitosan were explored. The information presented here will facilitate T. weissflogii molecular research and the exploitation of ß-chitin-derived high-value enzymes and products.

Climate-induced range shifts shaped the present and threaten the future genetic variability of a marine brown alga in the Northwest Pacific.

Glaciation-induced environmental changes during the last glacial maximum (LGM) have strongly influenced species' distributions and genetic diversity patterns in the northern high latitudes. However, these effects have seldom been assessed on sessile species in the Northwest Pacific. Herein, we chose the brown alga Sargassum thunbergii to test this hypothesis, by comparing present population genetic variability with inferred geographical range shifts from the LGM to the present, estimated with species distribution modelling (SDM). Projections for contrasting scenarios of future climate change were also developed to anticipate genetic diversity losses at regional scales. Results showed that S. thunbergii harbours strikingly rich genetic diversity and multiple divergent lineages in the centre-northern range of its distribution, in contrast with a poorer genetically distinct lineage in the southern range. SDM hindcasted refugial persistence in the southern range during the LGM as well as post-LGM expansion of 18 degrees of latitude northward. Approximate Bayesian computation (ABC) analysis further suggested that the multiple divergent lineages in the centre-northern range limit stem from post-LGM colonization from the southern survived lineage. This suggests divergence due to demographic bottlenecks during range expansion and massive genetic diversity loss during post-LGM contraction in the south. The projected future range of S. thunbergii highlights the threat to unique gene pools that might be lost under global changes.

MiR8181 is involved in the cell growth regulation of Saccharina japonica.

Aureochrome, a blue-light receptor specifically found in photosynthetic stramenopiles, plays an important role in algal growth and development. It holds a reversed effector-sensor topology for the reception of blue light, acting as a candidate of optogenetic tool in transcriptional regulation. However, the inner regulatory mechanism of aureochrome is still unclear. In this study, we explored the potential regulatory relationship between microRNAs (miRNAs) and mRNAs by small RNA, transcriptome and degradome sequencing in Saccharina japonica. Through screening miRNA-mRNA interaction networks at the whole-genome level, we found that 18 miRNAs perfectly paired with aureochrome. Among these screened miRNAs, miR8181 was negatively correlated with aureochrome5 with high credibility, exhibiting tissue-specific expression in sporophyte of S. japonica. Degradome analysis further revealed the exact cleavage site of miR8181 on aureochrome5, confirming their targeting relationship. For the 54 target genes of miR8181, nine genes that exhibited similar expression to that of aureochrome5 competed for the same binding site, thus establishing a competing endogenous RNA network. Functional enrichment of the target genes revealed that miR8181 was involved in the regulation of cell differentiation and development in S. japonica. Moreover, overexpression of miR8181 resulted in significant decreases in the cell growth rates of Phaeodactylum tricornutum, suggesting negative roles of miR8181 in regulating cell growth. Our study revealed that miR8181, the targeting miRNA of aureochrome5, played negative roles in cell growth and development.

Genome-wide identification of chitinase genes in Thalassiosira pseudonana and analysis of their expression under abiotic stresses.

BACKGROUND: The nitrogen-containing polysaccharide chitin is the second most abundant biopolymer on earth and is found in the cell walls of diatoms, where it serves as a scaffold for biosilica deposition. Diatom chitin is an important source of carbon and nitrogen in the marine environment, but surprisingly little is known about basic chitinase metabolism in diatoms. RESULTS: Here, we identify and fully characterize 24 chitinase genes from the model centric diatom Thalassiosira pseudonana. We demonstrate that their expression is broadly upregulated under abiotic stresses, despite the fact that chitinase activity itself remains unchanged, and we discuss several explanations for this result. We also examine the potential transcriptional complexity of the intron-rich T. pseudonana chitinase genes and provide evidence for two separate tandem duplication events during their evolution. CONCLUSIONS: Given the many applications of chitin and chitin derivatives in suture production, wound healing, drug delivery, and other processes, new insight into diatom chitin metabolism has both theoretical and practical value.

A Sulfated Polysaccharide from Saccharina japonica Suppresses LPS-Induced Inflammation Both in a Macrophage Cell Model via Blocking MAPK/NF-κB Signal Pathways In Vitro and a Zebrafish Model of Embryos and Larvae In Vivo.

Inflammation is a complicated host-protective response to stimuli and toxic conditions, and is considered as a double-edged sword. A sulfated Saccharinajaponica polysaccharide (LJPS) with a sulfate content of 9.07% showed significant inhibitory effects against lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 macrophage cells and zebrafish. Its chemical and structural properties were investigated via HPLC, GC, FTIR, and NMR spectroscopy. In vitro experiments demonstrated that LJPS significantly inhibited the generation of nitric oxide (NO) and prostaglandin E2 (PGE2) via the downregulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression and suppressed pro-inflammatory cytokines tumor necrosis factor (TNF)-α and interleukin (IL)-1ß production via the nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signal pathways in LPS-induced RAW 264.7 cells. Moreover, LJPS showed strong protective effects against LPS-induced inflammatory responses in zebrafish, increasing the survival rate, reducing the heart rate and yolk sac edema size, and inhibiting cell death and the production of intracellular reactive oxygen species (ROS) and NO. Its convenience for large-scale production and significant anti-inflammatory activity indicated the potential application of LJPS in functional foods, cosmetics, and pharmaceutical industries.