Xiuliang Wang

Fucoidan (FPS), a sulfated polysaccharide isolated from brown algae with a molecular weight ranging approximately from 5 to 200 kDa, exhibits diverse bioactivities, yet its high molecular weight (HMW) restricts topical bioavailability. This study explored the molecular-weight-dependent transdermal behavior of FPS and its underlying interaction mechanisms with the skin barrier. To address this, FPS fractions (6 to 103 kDa) were prepared via controlled oxidative degradation. In vitro permeation studies combined with Confocal Laser Scanning Microscopy (CLSM) visualization revealed a critical molecular weight threshold of approximately 11 kDa. HMW-FPS were mainly retained on the skin surface, whereas low molecular weight FPS (LMW-FPS, ≤11 kDa) penetrated into the viable epidermis and dermis. ATR-FTIR spectroscopy was employed to elucidate the underlying mechanism, which revealed that LMW-FPS overcomes the skin barrier through synergistic structural modulations: (1) it enhances intercellular lipid fluidity, accompanied by a reduction in CH₂ stretching vibration intensity; (2) it induces conformational changes in keratin via direct electrostatic interactions, promoting the transition from α-helices to β-sheets. Furthermore, histological evaluation confirmed that FPS treatment caused no obvious skin irritation. These findings demonstrate that LMW-FPS acts as a safe, reversible modulator of the stratum corneum (SC) barrier, providing a promising strategy for the design of polysaccharide-based transdermal delivery systems.

Aquaculture farms cultivating Saccharina japonica are highly active in Wando, Korea, and Rongcheng, China. However, the yield of S. japonica significantly declined in the Rongcheng region in 2022 compared to previous records, whereas that in Wando remained at a normal level, presumably due to the presence of a pathogenic microbiome. We used environmental DNA (eDNA) metagenomic analysis to compare the microbial compositions of seawater from aquaculture farms in Wando and Rongcheng. Seawater samples were collected from one Korean site in Wando (WA) and two Chinese sites in Ailian Bay (AB) and Lidao Bay (LB). Metagenomic analysis focusing on the microbial 16S rRNA identified 38 phyla and 58 families of microbiomes in all regions. Potentially pathogenic bacterial groups associated with S. japonica in AB and LB were more abundant than in WA, suggesting their potential influence on mortality and the decline in the harvest yield of S. japonica. The microbial composition of WA was distinguished from those of the other two sites, which clustered together with higher similarity. Since the S. japonica aquaculture industry is important for both countries, this comparative eDNA monitoring is a valuable initiation towards the next step of problem-solving practices in coastal management in these two aquaculture systems.

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.

CRY-DASH, a new cryptochrome blue light receptor, can repair damaged DNA and regulate secondary metabolism and development of fungus. However, its role in regulation during the growth of Saccharina japonica is still unclear. After cloning the full-length of CRY-DASH from S. japonica (sjCRY-DASH), we deduced that its open reading frame was 1779 bp long and encoded 592 amino acids. sjCRY-DASH transcription was rapidly upregulated within 30 min in response to blue light and exhibited 24 h periodicity with different photoperiods. Moreover, sjCRY-DASH maintained the same periodicity in suitable growth temperature, suggesting a close relationship between this periodicity and circadian rhythm regulation. Novel-m3234-5p, which was targeted to sjCRY-DASH, decreased with increasing sjCRY-DASH transcription, acting as a negative modulator of sjCRY-DASH. Six long non-coding RNAs classified as long intergenic non-coding RNAs (lincRNAs) exhibited co-expression with sjCRY-DASH. A miRNA sjCRY DASH lincRNA network was consequently identified. By predicting the endogenous competing mRNAs of novel-m3234-5p, we found that sjCRY-DASH indirectly participated in the regulation of DNA damage repair, protein synthesis and processing, and actin transport. In conclusion, our results revealed that non-coding RNAs participate in the regulation of sjCRY-DASH, which played vital roles in the growth and early development of S. japonica.

Background: Alginate is an important cell wall component and mannitol is a soluble storage carbon substance in the brown seaweed Saccharina japonica. Their contents vary with kelp developmental periods and harvesting time. Alginate and mannitol regulatory networks and molecular mechanisms are largely unknown. Results: With WGCNA and trend analysis of 20,940 known genes and 4264 new genes produced from transcriptome sequencing of 30 kelp samples from different stages and tissues, we deduced that ribosomal proteins, light harvesting complex proteins and “imm upregulated 3” gene family are closely associated with the meristematic growth and kelp maturity. Moreover, 134 and 6 genes directly involved in the alginate and mannitol metabolism were identified, respectively. Mannose-6-phosphate isomerase (MPI2), phosphomannomutase (PMM1), GDP-mannose 6-dehydrogenase (GMD3) and mannuronate C5-epimerase (MC5E70 and MC5E122) are closely related with the high content of alginate in the distal blade. Mannitol accumulation in the basal blade might be ascribed to high expression of mannitol-1-phosphate dehydrogenase (M1PDH1) and mannitol-1-phosphatase (M1Pase) (in biosynthesis direction) and low expression of mannitol-2-dehydrogenase (M2DH) and Fructokinase (FK) (in degradation direction). Oxidative phosphorylation and photosynthesis provide ATP and NADH for mannitol metabolism whereas glycosylated cycle and tricarboxylic acid (TCA) cycle produce GTP for alginate biosynthesis. RNA/protein synthesis and transportation might affect alginate complex polymerization and secretion processes. Cryptochrome (CRY-DASH), xanthophyll cycle, photosynthesis and carbon fixation influence the production of intermediate metabolite of fructose-6-phosphate, contributing to high content of mannitol in the basal blade. Conclusions: The network of co-responsive DNA synthesis, repair and proteolysis are presumed to be involved in alginate polymerization and secretion, while upstream light-responsive reactions are important for mannitol accumulation in meristem of kelp. Our transcriptome analysis provides new insights into the transcriptional regulatory networks underlying the biosynthesis of alginate and mannitol during S. japonica developments.

Tic20 is an important translocon protein that plays a role in protein transport in the chloroplast. The sequence of Tic20 was determined in the lower brown alga Saccharina japonica. Structural analysis of SjTic20 revealed a noncanonical structure consisting of an N-terminal non-cyanobacterium-originated EF-hand domain (a helix-loop-helix structural domain) and a C-terminal cyanobacterium-originated Tic20 domain. Subcellular localization and transmembrane analysis indicated that SjTic20 featured an “M”-type N_in-C_in-terminal orientation, with four transmembrane domains in the innermost membrane of the chloroplast in the microalga Phaeodactylum tricornutum, and the EF-hand domain was entirely extruded into the chloroplast stroma. Our study provides information on the structure, localization, and topological features of SjTic20, and further functional analysis of SjTic20 in S. japonica is needed.