Thallusin, isolated from a marine bacterium, is the only known natural product that acts as an algal morphogenesis-inducing factor. Recently, there has been a decrease in the number and variety of marine algae in the oceans of the world. Although the exact mechanism for this reduction in biodiversity is unclear, the biological investigation of thallusin, which controls the growth of marine algae, may help limit any further decline in their number. Because natural thallusin can only be obtained in exceedingly limited amounts from microbial cultivation (i.e., 0.14 mg from 180 L of culture fluid of the YM2-23 strain), a synthetic supply of thallusin is highly desirable. Against this backdrop, we embarked on the synthetic study of thallusin, and the asymmetric total synthesis of thallusin has been achieved based on the enzymatic hydrolysis resolution by the combination of lipase PS-30 and lipase MA-10. This synthetic strategy was further applied to the syntheses of thallusin analogues, facilitating to investigate the biological properties of thallusin. Furthermore, effective culture conditions for Monostroma latissimum, belonging to Ulotrichales, were explored by investigating the effects of nutrient salts such as Fe2⁺, Mn²⁺ and Co²⁺ in the culture medium supplemented with thallusin.

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Codium fragile is a green alga native to Japan, but it has flourished as an invasive species in ports around the world. In the intertidal zone where Codium grows, the irradiation varies from weak blue-green to strong white light due to changes in water depth caused by the tide. Codium can utilize green light for photosynthesis through the unique carotenoid siphonaxanthin in the light-harvesting complex. However, it does not exhibit the xanthophyll cycle, a typical photoprotective mechanism, and the mechanism of adaptation to strong light is completely unknown. In this study, we used laboratorycultivated filamentous Codium to investigate changes in pigment accumulation with the wavelength and intensity of light during culture. As a result, we found that only blue-green irradiation induced the decrease of siphonaxanthin and the complementary accumulation of an unknown carotenoid. This turned out to be 19-deoxysiphonaxanthin, a novel biosynthetic intermediate between lutein and siphonaxanthin. We also revealed that this precursor was bound to the light-harvesting complex. Further investigation is needed to link the accumulation of this pigment with photoprotective mechanisms. Changes in accumulated carotenoids due to intense blue-green light may have contributed to the evolution from dark green Codium to bright green land plants.

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Charophyte green algae (Streptophyta) include the closest relatives of land plants. Recent phylogenetic analyses concluded that the sister group to land plants is the Zygnematophyceae. Charophyte algae are important in exploring the origin and evolution of land plants. Approximately 500 to 600 million years ago, the ancestors of charophyte algae successfully colonized land and subsequently gave rise to land plants. Charophyte algae have diverse but relatively simple body plans and have been used in many areas of biological research. Recently, the genomes of the representative lineages of charophyte algae have been sequenced and these genome data have opened doors for studies that elucidate the evolution and function of genes in charophyte algae. This paper introduces charophyte algae and briefly reviews recent morphological and genomic studies on charophyte algae.

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Neopyropia tenuipedalis (Rhodophyta, Bangiales) is one of the local rarely nori species in Japan. In Yamaguchi Prefectuire, this species had been collected as food resource, which are called “Aka-nori”. Moreover, Yamaguchi Prefectural Fisheries Research Center begun the aquaculture trials in Yamaguchi Bay in 2002 and the amount of production had increased gradually year and year. However, production has continued to decrease since 2012. More recently, intense disappearance of thalli was due to predation by blackhead seabream, Acanthopagrus schlegelii. We had to develop some other techniques for stable producing of N. tenuipedalis. That is land-based cultivation of this species. This project was supported by the grant of the Science and Technology Research Promotion Program for Agriculture, Forestry, Fisheries, and Food Industry for three years. At that time, there were few reports about this species and we started the fundamental researches in every life-stage of it. And then, we were able to clarify the temperature characteristics in all life-stage of N. tenuipedalis with laboratory experiments. Although we have developed the land-based cultivation techniques, there are many problems such as stable growth, amino acids contents, the right of strain and so on. We keep the techniques improving for development of land-based cultivation using many seaweeds including N. tenuipedalis.

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Since the development of next-generation sequencing (NGS) technology, tremendous progress has been made in its sequencing capabilities and cost reduction. The application of these technologies to the study of macroalgae will greatly help our understanding of their taxonomy and ecology, as well as their application to aquaculture. We conducted RNA-seq analyses of the reference strain U51 and the high water temperature tolerant strain MET11 to research genes that responsive to high temperature stress in the marine red algae Neopyropia yezoensis (susabi-nori). The results showed clear differences in the expression levels of genes involved in high temperature stress between U51 and MET11. On the other hand, we also investigated whether there are genetic differences between male and female cells on the same blade by RNA-seq and single nucleotide polymorphism (SNP) analysis using the marine red alga Pyropia katadae. However, these analyses have yet to find genetic differences between male and female cells, and we would like to try other approaches such as genomic analysis. Although our research has just begun, we hope to contribute to the study of macroalgae through NGS-based analysis in the future.

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Our research group at Saga University studies the genomes of seaweeds of the genus Pyropia. In this review, we describe our research in Japanese, focusing on the results we have published as research articles in the past. Because this is a rare opportunity to explain in Japanese, we decided to present some of the candid stories that we could not include in the publications. Firstly, we wrote about the importance of genomics from our point of view. Secondly, we explain the confusion in the taxonomy of the genus Pyropia. Thirdly, we present comparisons of chloroplast, mitochondrial and nuclear genomes among the varieties of Susabi-nori (Pyropia yezoensis ). Fourthly, we present what we have learned from the genome analysis of hybrid strains of Susabi-nori and Asakusa-nori (Pyropia tenera ). Fifthly, we review the transcriptome analysis of Pyropia species. Finally, we discuss future prospects for the breeding of Pyropia species.

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In the southern area of Hokkaido, Makombu (Saccharina japonica) is mainly farmed. During the winter season (from January to March), dulse (Devaleraea inkyuleei), a type of red algae, naturally grows on the ropes used for Makombu farming. Fishermen were removing the overgrown dulse as an obstruction. Therefore, we have recently begun exploring the health benefits of dulse to advance its use as a functional food material. As a result, we found that Hokkaido dulse is rich in protein and carbohydrate (about 40％ per dry weight, respectively). The major component of protein was phycoerythrin (PE), and then we determined the primary structure and 3D structure of it. In addition, we determined the entire structure of chloroplast DNA, in which the gene of PE is encoded. Furthermore, we found that dulse PE has hypotensive, antioxidant, anti-inflammatory, and brain function-improving effects. On the other hand, the major component of carbohydrate was xylan of polysaccharide. Therefore, we prepared oligosaccharides by enzymatic degradation of the dulse xylan. From this oligosaccharide, we isolated β - (1→3)/β - (1→4)-xylotriose (DX3), which has a β - (1→3) bond at the non-reducing end and a β - (1→4) bond at the reducing end. Furthermore, we clarified that DX3 selectively promotes the growth of Bifidobacterium adolescentis. Based on these findings, we believe that detailed investigation of the biochemical properties of Hokkaido dulse will contribute to the development of protein sources for future food shortages and to the development of food materials that make people healthier, and we are continuing our research.

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Cladosiphon okamuranus is a major cultivated seaweed in the Ryukyu Islands. There has been a marked fluctuation in annual production in recent years. To resolve the problem, our research group investigated the effect of light irradiance and color on the development of an erect thallus from a discoid germling and nutrient uptake characteristics of the sporophyte. Discoid germlings cultured with rich nutrients showed higher germination rates of erect thalli than those in sterilized seawater. This result indicates that the nutrient is required to develop the erect thallus. Moreover, the low irradiance and blue light conditions might promote the development of an erect thallus. This finding coincides with our past study and the fishermen's rule that the cultivation nets at the nursery stage are installed in deep areas. Uptake rates of NH₄⁺ and PO₄^3- in the sporophytes increased as the substrate concentration increased, whereas NO₃^- uptake rates increased until about 20 μM and then gradually decreased. The relatively higher uptake rates for NH₄⁺ may indicate an adaptive property for efficient absorption of transient NH₄⁺ supply from groundwater discharge in the subtropical Ryukyu Islands under low nitrate conditions. Collectively, our findings indicate the importance of environmental condition on the development of erect thallus and the nutrient uptake of sporophyte. Therefore, this study has the possibility to contribute for the stabilization of productivity.

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Seaweeds are abundant in cell wall polysaccharides, which play an important role in the different fields of industries because of their physiochemical and biofunctional properties. Cladosiphon okamuranus, Okinawa mozuku in Japanese, is utilized edible brown algae in Japan and species in Ryukyu archipelago. Cladosiphon okamuranus possesses the highest content of fucoidan among any brown algal species. Fucoidan is a sulfated polysaccharide consisting of fucose in the main chain substituted by glucuronic acid and exists as a matrix polysaccharide in the cell wall. Fucoidan have been extensively explored for numerous therapeutic effects and bioactivities; consequently, C. okamuranus plays a key role in the fields of pharmaceutical, nutraceutical cosmeceutical, and functional food. However, fucoidan in these studies were mostly extracted with HCl or water and analyzed as an individual polymer. Therefore, we analyzed the whole cell wall of C. okamuranus with the structural differences in predominant polysaccharide types. Here, the cell wall polysaccharide of seaweeds particularly fucoidan is described, focusing on our results of cell wall studies of C. okamuranus.

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In the seedling production method using Solution Extracted from Homogenized Thalli (SEHT), we examined the light quantity and light source tissue culture conditions to increase branch formation from U. prolifera subfragments. For light quantity, the average of branch formation rate was 0％ at 0 μmol m^-2 s^-1, 0.4％ at 10 μmol m^-2 s^-1, increasing to 14.4％ at 25 μmol m^-2 s^-1 and reached 60.4％ at 50 μmol m^-2 s^-1. Subsequently, it increased gently to 70.0％ at 100 μmol m^-2 s^-1. For light sources, the average of branch formation was 30.4％ under fluorescent light, 21.6％ under white LEDs, 27.6％ under red LEDs, 10.0％ under green LEDs, 26.8％ under blue LEDs. As a result of Steel-Dwass multiple comparisons test, the average of branch formation rate was almost constant of the various the light sources. However, blue LEDs promoted branch growth of U. prolifera subfragments. In the seedling production method using SEHT, we recommend culture conditions for increased branch formation of U. prolifera subfragments as light quantity of over 50 μmol m^-2 s^-1 and a light source of blue LEDs.

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