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Koji Mikami

Hokkaido University, Faculty of Fisheries Sciences, Faculty Member

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Dr. Koji Mikami is a faculty member of the Faculty of Fisheries Sciences, Hokkaido University, Japan. Before 2006, his studied development and environmental stress response in terrestrial plants, like angiosperm Arabidopsis thaliana and moss Physcomitrella patens, most of which were done at the National Institute for Basic Biology, Okazaki, Japan, University of California, Berkeley, USA and Free University of Berlin, Germany. After joining to the Faculty of Fisheries Sciences, Hokkaido University from 2006, his main interests changed to physiological and molecular biological researches on marine plants, especially red seaweeds. His efforts have paid for elucidation of regulatory mechanisms of diploid-haploid life cycle and also for development of transient gene expression systems. Additional fields of interest are the mechanisms of stress tolerance in seaweeds.

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Papers by Koji Mikami

A unique life cycle transition in the red seaweed Pyropia yezoensis depends on apospory

Communications Biology, 2019

Plant life cycles consist of two temporally separated stages: a haploid gametophyte and a diploid... more Plant life cycles consist of two temporally separated stages: a haploid gametophyte and a diploid sporophyte. In plants employing a haploid-diploid sexual life cycle, the transition from sporophyte to gametophyte generally depends on meiosis. However, previous work has shown that in the red seaweed Pyropia yezoensis, this transition is independent of meiosis, though how and when it occurs is unknown. Here, we explored this question using transcriptomic profiling of P. yezoensis gametophytes, sporophytes, and conchosporangia parasitically produced on sporophytes. We identify a knotted-like homeobox gene that is predominately expressed in the conchosporangium and may determine its identity. We also find that spore-like single cells isolated from the conchosporangium develop directly into gametophytes, indicating that the gametophyte identity is established before the release of conchospores and prior to the onset of meiosis. Based on our findings, we propose a triphasic life cycle for P. yezoensis involving production of gametophytes by apospory.

Dietary supplementation of red alga Pyropia spheroplasts on growth, feed utilization and body composition of sea cucumber, Apostichopus japonicus (Selenka)

Aquaculture Research

A feeding experiment was conducted in closed recirculating system to evaluate the effects of free... more A feeding experiment was conducted in closed recirculating system to evaluate the effects of freeze dried Pyropia spheroplasts (PS) on growth and biochemical composition of sea cucumber Apostichopus japonicus. PS was prepared through enzymatic treatment to break down the complex mixture of polysaccharide cell wall. Sea cucumbers were fed formulated diets with 10 (Diet 1), 30 (Diet 2) and 50 g kg-1 (Diet 3) inclusion level of PS in closed recirculating systems. A diet without PS was used as a control (Diet 4). The experiment was conducted for 6 weeks maintaining water temperature 15±1 o C, photoperiod 18:06 h (D:L). Feed were supplied ad-libitum at 16 h once in a day and excess feed and feces were removed in the next morning. Results showed that highest growth was observed in the 50 g kg-1 PS diet compared to other treatments. Total weight gain, mean weight gain, net yield, protein efficiency ratio (PER) and protein gain (%) was significantly higher in 50 g kg-1 PS diet (P<0.05). Significantly higher percentage of energy was allocated for growth in the diet 3. The highest specific growth rate, feed conversion efficiency (P<0.05) was observed in higher percentage of PS diet. Both the growth performance and biochemical analysis showed that 2 superior growth was observed with increasing the level of PS in the diet. This is comprehensible that PS can be used as a new, cheaper feed ingredient in the formulated diet of A. japonicus for commercial aquaculture.

Corresponding author

Visualization of Phosphoinositides via the Development of the Transient

Instructions for use Title Photosynthesis-dependent Ca 2 + influx and functional diversity between phospholipases in the formation of cell polarity in migrating cells of red algae

Unicellular spore cells, designated as monospores (also called archeospores), are well known as m... more Unicellular spore cells, designated as monospores (also called archeospores), are well known as migrating plant cells, in which establishment of the anterior-posterior axis directs asymmetrical distribution of F-actin. Since the mechanisms of cell polarity formation are not yet fully elucidated in monospores, we investigated the roles of phosphoinositide signaling systems and Ca mobilization in migration. Although we have already found the critical involvement of phosphatidylinositol 3-kinase in the establishment of cell polarity, we recently demonstrated the important roles of extracellular Ca influx, phospholipase C (PLC) and phospholipase D (PLD). The remarkable characteristics of these factors are that Ca influx depends on photosynthetic activity and that PLC and PLD play roles in the establishment and maintenance of cell polarity, respectively. These findings could provide new insight into the regulation of migration in eukaryotic cells. TEXT Monospores are responsible for asex...

Migrating Plant Cell: F-Actin Asymmetry Directed by Phosphoinositide Signaling

Polarity is a fundamental cell property essential for differentiation, proliferation and morphoge... more Polarity is a fundamental cell property essential for differentiation, proliferation and morphogenesis in unicellular and multicellular organisms. It is well known that polarized distribution of F-actin is important in providing the driving force for directional migration in mammalian leukocytes and Dictyostelium cells. Phosphoinositide (PI) signaling, including phosphatidylinositol kinases and phospholipases, is also critical for the formation of cell polarity in these cells. A monospore from the marine red alga Porphyra yezoensis is well known as a migrating plant cell and thus is a unique and useful material for investigating polarity determination in plant cells. As in leukocytes and Dictyostelium cells, monospore migration requires asymmetrical distribution of F-actin, whose establishment is regulated by the phosphatidylinositol 3-kinase and phospholipase C, whereas

Editorial: Environmental Stress-Promoting Responses in Algae

Frontiers in Marine Science

Pyropia yezoensis var. irifuneiensis (Bangiales, Rhodophyta), a naturally occurring variety with large ovate shape from Hokkaido, Japan

Gametophytic thalli with a large ovate shape were collected at the Irifune fishing port at Hakoda... more Gametophytic thalli with a large ovate shape were collected at the Irifune fishing port at Hakodate in Hokkaido, Japan. Phylogenetic analysis using rbcL sequences identified this alga as the red seaweed Pyropia yezoensis (order Bangiales). Since the morphology of the Irifune specimen was different from that of generally recognized P. yezoensis specimens, indicating a naturally occurring variety of P. yezoensis, the alga was named Pyropia yezoensis (Ueda) M. S. Hwang & H. G. Choi var. irifuneiensis K. Mikami & H. Nakao. Morphological characteristics of conchocelis filaments and conchosporangia were identical to those of P. yezoensis f. narawaensis, although the division formula for female gametangia was slightly different. During early development, vertical cell division was frequently observed in the upper parts of thalli, establishing the cuneate and then ovate shape. However, this morphological change was inhibited at 20°C, resulting in production of slender thalli and suggesting ...

The Absence of Hydrodynamic Stress Promotes Acquisition of Freezing Tolerance and Freeze-Dependent Asexual Reproduction in the Red Alga ‘Bangia’ sp. ESS1

Plants

The ebb tide causes calm stress to intertidal seaweeds in tide pools; however, little is known ab... more The ebb tide causes calm stress to intertidal seaweeds in tide pools; however, little is known about their physiological responses to loss of water movement. This study investigated the effects of static culture of ‘Bangia’ sp. ESS1 at 15 °C on tolerance to temperature fluctuation. The freezing of aer-obically cultured thalli at −80 °C for 10 min resulted in the death of most cells. By contrast, statically cultured thalli acquired freezing tolerance that increased cell viability after freeze–thaw cycles, although they did not achieve thermotolerance that would enable survival at the lethal temperature of 32 °C. Consistently, the unsaturation of membrane fatty acids occurred in static culture. Notably, static culture of thalli enhanced the release of asexual spores after freeze-and-thaw treatment. We conclude that calm stress triggers both the acquisition of freezing tolerance and the promotion of freezing-dependent asexual reproduction. These findings provide novel insights into str...

Reproductive Responses to Wounding and Heat Stress in Gametophytic Thalli of the Red Alga Pyropia yezoensis

Frontiers in Marine Science

The timing of the transition from growth to reproduction is essential for the regulation of the s... more The timing of the transition from growth to reproduction is essential for the regulation of the seaweed life cycle. Variable environmental conditions can stress seaweeds and promote trade-offs between their growth and reproduction. Here, we demonstrate that reproductive responses can be induced by environmental stresses in the gametophytic thalli of the marine red alga Pyropia yezoensis. Excision of explants accelerated release of asexual monospores and sexual carpospores. The algal sensitivity to wounding was enhanced by a 3-day dark treatment prior to the excision of the explants. By contrast, heat stress at 25°C stimulated the production of a callus, a three-dimensional aggregation of randomly divided cells with multiple cell layers. This callus produced new gametophytic thalli with a normal shape; therefore, callus formation is thought to be one of the asexual reproductive strategies used by the alga to increase the number of thalli under heat stress conditions. Our results demonstrate that wounding and heat stress can reset the timing of reproduction and that gametophytic thalli therefore use a variety of distinct reproductive strategies under different stress conditions. These findings provide insights into the induction of reproduction by environmental stresses as a life cycle trade-off in seaweeds.

Heat-stress memory is responsible for acquired thermotolerance in Bangia fuscopurpurea

Journal of Phycology

The environmental stresses that sessile organisms experience usually fluctuate dramatically and a... more The environmental stresses that sessile organisms experience usually fluctuate dramatically and are often recurrent. Terrestrial plants can acquire memory of exposure to sublethal heat stress to acquire thermotolerance and survive subsequent lethal high‐temperature stress; however, little is known concerning whether seaweeds acquire thermotolerance via heat‐stress memory. We have demonstrated that the red seaweed Bangia fuscopurpurea can indeed acquire memory of sublethal high‐temperature stress, resulting in the acquisition of thermotolerance that protects against subsequent lethal high‐temperature stress. Moreover, the maintenance of heat‐stress memory was associated with a slight increase in the saturation level of membrane fatty acids. This suggests that the modification of membrane fluidity via changes in membrane fatty acid composition is involved in the establishment and maintenance of heat‐stress memory in B. fuscopurpurea. These findings provide insights into the physiological survival and growth strategies of sessile red seaweeds to cope with recurrent changes in environmental conditions.

Discolored Red Seaweed Pyropia yezoensis with Low Commercial Value Is a Novel Resource for Production of Agar Polysaccharides

Marine biotechnology (New York, N.Y.), 2018

The red seaweed Pyropia yezoensis has been demonstrated to be a novel resource for the production... more The red seaweed Pyropia yezoensis has been demonstrated to be a novel resource for the production of high-quality agar. P. yezoensis is grown for the food industry in large-scale Japanese mariculture operations. However, discolored P. yezoensis is mostly discarded as an industrial waste, although it has some kind of utility values. Here, we evaluated the utility of discolored P. yezoensis as a resource for agar production. The quality of agar from the discolored seaweed was comparable to that from normal seaweed. In addition, as a distinguishing characteristic, agar yield was higher from discolored seaweeds than from normal types. Moreover, we successfully used agar from discolored P. yezoensis for bacterial plate media and DNA electrophoresis gels without agarose purification. Thus, our results demonstrate that discolored P. yezoensis is suitable for agar production and use in life science research. Diverting discolored P. yezoensis from disposal to agar production provides a solut...

The presence of free d-aspartate in marine macroalgae is restricted to the Sargassaceae family

Bioscience, biotechnology, and biochemistry, 2018

The presence of d-aspartate (d-Asp), a biologically rare amino acid, was evaluated in 38 species ... more The presence of d-aspartate (d-Asp), a biologically rare amino acid, was evaluated in 38 species of marine macroalgae (seaweeds). Despite the ubiquitous presence of free l-Asp, free d-Asp was detected in only 5 species belonging to the Sargassaceae family of class Phaeophyceae (brown algae) but not in any species of the phyla Chlorophyta (green algae) and Rhodophyta (red algae). All other members of Phaeophyceae, including 3 species classified into the section Teretia of Sargassaceae did not contain d-Asp. These results indicate that the presence of free d-Asp in marine macroalgae is restricted only to the Sargassaceae family, excluding the species in the section Teretia.

Parthenosporophytes of the brown alga Ectocarpus siliculosus exhibit sex-dependent differences in thermotolerance as well as fatty acid and sterol composition

Marine environmental research, Jan 10, 2018

In the filamentous brown alga Ectocarpus siliculosus, male and female sex is expressed during the... more In the filamentous brown alga Ectocarpus siliculosus, male and female sex is expressed during the haploid parthenosporophyte phase of the life cycle. Here, we found that male parthenosporophytes displayed thermotolerance whereas female specimens displayed severely reduced viability at 25 °C and 28 °C. Profiling of polyunsaturated fatty acids showed that n-3 and n-6 were the predominant species in male and female parthenosporophytes, respectively, and that the n-3/n-6 fatty acid ratio was not affected by a temperature change. Both male and female parthenosporophytes contained the sterols fucosterol, cholesterol, and ergosterol, but these were present at higher levels at 10-25 °C in female specimens than in males. Thus, these fatty acids and sterols would be expected to make the membranes more rigid in the female compared to the male, which is opposite to the paradigm that increased rigidity confers thermotolerance. Our results suggest that the sex-dependent thermotolerance in E. sili...

Primary Characterization of a Life-Cycle Mutant akasusabi of the Red Alga Neopyropia yezoensis

Phycology

Gametophyte-to-sporophyte transition in the haploid-diploid life cycle depends on fertilization o... more Gametophyte-to-sporophyte transition in the haploid-diploid life cycle depends on fertilization of male and female gametes. We describe here a mutant of the marine red seaweed Neopyropia yezoensis, designated akasusabi (aks), where the gametophyte-to-sporophyte transition occurs independently of fertilization. Although conchocelis filaments were produced from carpospores, severe defects in the maturation of carposporangia via mitosis to generate conchospores were observed. In the aks mutant, however, somatic cells of gametophytic thalli were able to produce conchocelis filaments without fertilization. Thus, apogamy occurs in aks. In addition, aks was highly sensitive to wounding that promotes both asexual and apogamous reproductive responses by producing spores, which develop either into blades or conchocelis filaments, indicating that aks responds to wounding by enhanced reproduction. These findings indicated that the aks mutation enables the transformation of vegetative cells to c...

Migrating Plant Cell: F-Actin Asymmetry Directed by Phosphoinositide Signaling

Polarity is a fundamental cell property essential for differentiation, proliferation and morphoge... more Polarity is a fundamental cell property essential for differentiation, proliferation and morphogenesis in unicellular and multicellular organisms. It is well known that polarized distribution of F-actin is important in providing the driving force for directional migration in mammalian leukocytes and Dictyostelium cells. Phosphoinositide (PI) signaling, including phosphatidylinositol kinases and phospholipases, is also critical for the formation of cell polarity in these cells. A monospore from the marine red alga Porphyra yezoensis is well known as a migrating plant cell and thus is a unique and useful material for investigating polarity determination in plant cells. As in leukocytes and Dictyostelium cells, monospore migration requires asymmetrical distribution of F-actin, whose establishment is regulated by the phosphatidylinositol 3-kinase and phospholipase C, whereas Koji Mikami 206 phospholipase D is involved in the maintenance of F-actin distribution. These findings indicate that the regulation of F-actin asymmetry by PI signaling cascades is evolutionarily conserved in terms of the establishment of cell polarity in migrating eukaryotic cells.

Oxidative Stress Promotes Asexual Reproduction and Apogamy in the Red Seaweed Pyropia yezoensis

Frontiers in plant science, 2017

The marine red seaweed Pyropia yezoensis has a haploid-diploid life cycle wherein two heteromorph... more The marine red seaweed Pyropia yezoensis has a haploid-diploid life cycle wherein two heteromorphic generations, a haploid gametophyte and a diploid sporophyte, are reciprocally generated from conchospores and carpospores, respectively. When we treated gametophytic blades of P. yezoensis with H2O2, discharge of asexual monospores was accelerated, resulting in increased numbers of gametophytic clones. Production of sporophytes without fertilization of male and female gametes was also observed. These findings indicate that oxidative stress can induce vegetative cells to develop into monospores that produce gametophytes asexually and can sometimes prompt carpospores to develop into sporophytes. The discovery of oxidative stress-triggered asexual reproduction and -apogamy will stimulate progress in studies of life-cycle regulation in P. yezoensis.

Photosynthesis-Dependent Extracellular Ca2+ Influx Triggers an Asexual Reproductive Cycle in the Marine Red Macroalga Porphyra yezoensis

American Journal of Plant Sciences, 2010

Asexual propagation to increase the number of gametophytic clones via the growth of asexual haplo... more Asexual propagation to increase the number of gametophytic clones via the growth of asexual haploid spores is a unique survival strategy found in marine multicellular algae. However, the mechanisms regulating the asexual life cycle are largely unknown. Here, factors involved in the regulation of production and discharge of asexual spores, so-called monospores, are identified in the marine red macroalga Porphyra yezoensis. First, enhanced discharge of monospores was found by incubation of gametophytes in ASPMT1, a modified version of the previously established synthetic medium ASP 12 . Comparison of the compositions of ASPMT1 and our standard medium, ESL, indicated that the Ca 2+ concentration in ASPMT1 was three times lower than that in ESL medium. Thus, we modified ASPMT1 by increasing its Ca 2+ concentration, resulting in reduction of monospore discharge. These findings demonstrate the role of reduced Ca 2+ concentrations in enhancing monospore production and release. Moreover, it was also observed that initiation of asexual life cycle required illumination, was repressed by DCMU, and was induced by a Ca 2+ ionophore in the dark. Taken together, these results indicate that photosynthesis-dependent Ca 2+ influx triggers the asexual life cycle by promoting the production and discharge of monospores in P.

Characterization of an eukaryotic PL-7 Alginate Lyase in the Marine Red Alga Pyropia Yezoensis

Current Biotechnology, 2015

Identification and Efficient Utilization of Antibiotics for the Development of a Stable Transformation System in Porphyra yezoensis (Bangiales, Rhodophyta)

Journal of Aquaculture Research & Development, 2011

Heterologous activation of the Porphyra tenera HSP70 promoter in Bangiophycean algal cells

Bioengineered bugs

Porphyra has attracted great attention for its biological and industrial importance. However, est... more Porphyra has attracted great attention for its biological and industrial importance. However, establishment of a stable nuclear transformation has not yet been achieved in these organisms, which impedes the molecular biological study and the development of a molecular breeding method for them. Toward establishing the stable transformation, we have recently developed an efficient transient gene expression system in Bangiophycean algae, in which the HSP70 promoter from P. tenera (PtHSP70 promoter) was activated heterologously in P. yezoensis cells. Since heterologous promoters are required for homologous recombination-based stable transformation, the identification of heterologously activated promoters is important in establishing a stable transformation system in individual Bangiophycean alga. We here examined the activation of the PtHSP70 promoter using the GC-rich PyGUS reporter system in additional Porphyra and Bangia species. The results indicated that this promoter drove express...

A unique life cycle transition in the red seaweed Pyropia yezoensis depends on apospory

Communications Biology, 2019

Plant life cycles consist of two temporally separated stages: a haploid gametophyte and a diploid... more Plant life cycles consist of two temporally separated stages: a haploid gametophyte and a diploid sporophyte. In plants employing a haploid-diploid sexual life cycle, the transition from sporophyte to gametophyte generally depends on meiosis. However, previous work has shown that in the red seaweed Pyropia yezoensis, this transition is independent of meiosis, though how and when it occurs is unknown. Here, we explored this question using transcriptomic profiling of P. yezoensis gametophytes, sporophytes, and conchosporangia parasitically produced on sporophytes. We identify a knotted-like homeobox gene that is predominately expressed in the conchosporangium and may determine its identity. We also find that spore-like single cells isolated from the conchosporangium develop directly into gametophytes, indicating that the gametophyte identity is established before the release of conchospores and prior to the onset of meiosis. Based on our findings, we propose a triphasic life cycle for P. yezoensis involving production of gametophytes by apospory.

Dietary supplementation of red alga Pyropia spheroplasts on growth, feed utilization and body composition of sea cucumber, Apostichopus japonicus (Selenka)

Aquaculture Research

A feeding experiment was conducted in closed recirculating system to evaluate the effects of free... more A feeding experiment was conducted in closed recirculating system to evaluate the effects of freeze dried Pyropia spheroplasts (PS) on growth and biochemical composition of sea cucumber Apostichopus japonicus. PS was prepared through enzymatic treatment to break down the complex mixture of polysaccharide cell wall. Sea cucumbers were fed formulated diets with 10 (Diet 1), 30 (Diet 2) and 50 g kg-1 (Diet 3) inclusion level of PS in closed recirculating systems. A diet without PS was used as a control (Diet 4). The experiment was conducted for 6 weeks maintaining water temperature 15±1 o C, photoperiod 18:06 h (D:L). Feed were supplied ad-libitum at 16 h once in a day and excess feed and feces were removed in the next morning. Results showed that highest growth was observed in the 50 g kg-1 PS diet compared to other treatments. Total weight gain, mean weight gain, net yield, protein efficiency ratio (PER) and protein gain (%) was significantly higher in 50 g kg-1 PS diet (P<0.05). Significantly higher percentage of energy was allocated for growth in the diet 3. The highest specific growth rate, feed conversion efficiency (P<0.05) was observed in higher percentage of PS diet. Both the growth performance and biochemical analysis showed that 2 superior growth was observed with increasing the level of PS in the diet. This is comprehensible that PS can be used as a new, cheaper feed ingredient in the formulated diet of A. japonicus for commercial aquaculture.

Corresponding author

Visualization of Phosphoinositides via the Development of the Transient

Instructions for use Title Photosynthesis-dependent Ca 2 + influx and functional diversity between phospholipases in the formation of cell polarity in migrating cells of red algae

Unicellular spore cells, designated as monospores (also called archeospores), are well known as m... more Unicellular spore cells, designated as monospores (also called archeospores), are well known as migrating plant cells, in which establishment of the anterior-posterior axis directs asymmetrical distribution of F-actin. Since the mechanisms of cell polarity formation are not yet fully elucidated in monospores, we investigated the roles of phosphoinositide signaling systems and Ca mobilization in migration. Although we have already found the critical involvement of phosphatidylinositol 3-kinase in the establishment of cell polarity, we recently demonstrated the important roles of extracellular Ca influx, phospholipase C (PLC) and phospholipase D (PLD). The remarkable characteristics of these factors are that Ca influx depends on photosynthetic activity and that PLC and PLD play roles in the establishment and maintenance of cell polarity, respectively. These findings could provide new insight into the regulation of migration in eukaryotic cells. TEXT Monospores are responsible for asex...

Migrating Plant Cell: F-Actin Asymmetry Directed by Phosphoinositide Signaling

Polarity is a fundamental cell property essential for differentiation, proliferation and morphoge... more Polarity is a fundamental cell property essential for differentiation, proliferation and morphogenesis in unicellular and multicellular organisms. It is well known that polarized distribution of F-actin is important in providing the driving force for directional migration in mammalian leukocytes and Dictyostelium cells. Phosphoinositide (PI) signaling, including phosphatidylinositol kinases and phospholipases, is also critical for the formation of cell polarity in these cells. A monospore from the marine red alga Porphyra yezoensis is well known as a migrating plant cell and thus is a unique and useful material for investigating polarity determination in plant cells. As in leukocytes and Dictyostelium cells, monospore migration requires asymmetrical distribution of F-actin, whose establishment is regulated by the phosphatidylinositol 3-kinase and phospholipase C, whereas

Editorial: Environmental Stress-Promoting Responses in Algae

Frontiers in Marine Science

Pyropia yezoensis var. irifuneiensis (Bangiales, Rhodophyta), a naturally occurring variety with large ovate shape from Hokkaido, Japan

Gametophytic thalli with a large ovate shape were collected at the Irifune fishing port at Hakoda... more Gametophytic thalli with a large ovate shape were collected at the Irifune fishing port at Hakodate in Hokkaido, Japan. Phylogenetic analysis using rbcL sequences identified this alga as the red seaweed Pyropia yezoensis (order Bangiales). Since the morphology of the Irifune specimen was different from that of generally recognized P. yezoensis specimens, indicating a naturally occurring variety of P. yezoensis, the alga was named Pyropia yezoensis (Ueda) M. S. Hwang & H. G. Choi var. irifuneiensis K. Mikami & H. Nakao. Morphological characteristics of conchocelis filaments and conchosporangia were identical to those of P. yezoensis f. narawaensis, although the division formula for female gametangia was slightly different. During early development, vertical cell division was frequently observed in the upper parts of thalli, establishing the cuneate and then ovate shape. However, this morphological change was inhibited at 20°C, resulting in production of slender thalli and suggesting ...

The Absence of Hydrodynamic Stress Promotes Acquisition of Freezing Tolerance and Freeze-Dependent Asexual Reproduction in the Red Alga ‘Bangia’ sp. ESS1

Plants

The ebb tide causes calm stress to intertidal seaweeds in tide pools; however, little is known ab... more The ebb tide causes calm stress to intertidal seaweeds in tide pools; however, little is known about their physiological responses to loss of water movement. This study investigated the effects of static culture of ‘Bangia’ sp. ESS1 at 15 °C on tolerance to temperature fluctuation. The freezing of aer-obically cultured thalli at −80 °C for 10 min resulted in the death of most cells. By contrast, statically cultured thalli acquired freezing tolerance that increased cell viability after freeze–thaw cycles, although they did not achieve thermotolerance that would enable survival at the lethal temperature of 32 °C. Consistently, the unsaturation of membrane fatty acids occurred in static culture. Notably, static culture of thalli enhanced the release of asexual spores after freeze-and-thaw treatment. We conclude that calm stress triggers both the acquisition of freezing tolerance and the promotion of freezing-dependent asexual reproduction. These findings provide novel insights into str...

Reproductive Responses to Wounding and Heat Stress in Gametophytic Thalli of the Red Alga Pyropia yezoensis

Frontiers in Marine Science

The timing of the transition from growth to reproduction is essential for the regulation of the s... more The timing of the transition from growth to reproduction is essential for the regulation of the seaweed life cycle. Variable environmental conditions can stress seaweeds and promote trade-offs between their growth and reproduction. Here, we demonstrate that reproductive responses can be induced by environmental stresses in the gametophytic thalli of the marine red alga Pyropia yezoensis. Excision of explants accelerated release of asexual monospores and sexual carpospores. The algal sensitivity to wounding was enhanced by a 3-day dark treatment prior to the excision of the explants. By contrast, heat stress at 25°C stimulated the production of a callus, a three-dimensional aggregation of randomly divided cells with multiple cell layers. This callus produced new gametophytic thalli with a normal shape; therefore, callus formation is thought to be one of the asexual reproductive strategies used by the alga to increase the number of thalli under heat stress conditions. Our results demonstrate that wounding and heat stress can reset the timing of reproduction and that gametophytic thalli therefore use a variety of distinct reproductive strategies under different stress conditions. These findings provide insights into the induction of reproduction by environmental stresses as a life cycle trade-off in seaweeds.

Heat-stress memory is responsible for acquired thermotolerance in Bangia fuscopurpurea

Journal of Phycology

The environmental stresses that sessile organisms experience usually fluctuate dramatically and a... more The environmental stresses that sessile organisms experience usually fluctuate dramatically and are often recurrent. Terrestrial plants can acquire memory of exposure to sublethal heat stress to acquire thermotolerance and survive subsequent lethal high‐temperature stress; however, little is known concerning whether seaweeds acquire thermotolerance via heat‐stress memory. We have demonstrated that the red seaweed Bangia fuscopurpurea can indeed acquire memory of sublethal high‐temperature stress, resulting in the acquisition of thermotolerance that protects against subsequent lethal high‐temperature stress. Moreover, the maintenance of heat‐stress memory was associated with a slight increase in the saturation level of membrane fatty acids. This suggests that the modification of membrane fluidity via changes in membrane fatty acid composition is involved in the establishment and maintenance of heat‐stress memory in B. fuscopurpurea. These findings provide insights into the physiological survival and growth strategies of sessile red seaweeds to cope with recurrent changes in environmental conditions.

Discolored Red Seaweed Pyropia yezoensis with Low Commercial Value Is a Novel Resource for Production of Agar Polysaccharides

Marine biotechnology (New York, N.Y.), 2018

The red seaweed Pyropia yezoensis has been demonstrated to be a novel resource for the production... more The red seaweed Pyropia yezoensis has been demonstrated to be a novel resource for the production of high-quality agar. P. yezoensis is grown for the food industry in large-scale Japanese mariculture operations. However, discolored P. yezoensis is mostly discarded as an industrial waste, although it has some kind of utility values. Here, we evaluated the utility of discolored P. yezoensis as a resource for agar production. The quality of agar from the discolored seaweed was comparable to that from normal seaweed. In addition, as a distinguishing characteristic, agar yield was higher from discolored seaweeds than from normal types. Moreover, we successfully used agar from discolored P. yezoensis for bacterial plate media and DNA electrophoresis gels without agarose purification. Thus, our results demonstrate that discolored P. yezoensis is suitable for agar production and use in life science research. Diverting discolored P. yezoensis from disposal to agar production provides a solut...

The presence of free d-aspartate in marine macroalgae is restricted to the Sargassaceae family

Bioscience, biotechnology, and biochemistry, 2018

The presence of d-aspartate (d-Asp), a biologically rare amino acid, was evaluated in 38 species ... more The presence of d-aspartate (d-Asp), a biologically rare amino acid, was evaluated in 38 species of marine macroalgae (seaweeds). Despite the ubiquitous presence of free l-Asp, free d-Asp was detected in only 5 species belonging to the Sargassaceae family of class Phaeophyceae (brown algae) but not in any species of the phyla Chlorophyta (green algae) and Rhodophyta (red algae). All other members of Phaeophyceae, including 3 species classified into the section Teretia of Sargassaceae did not contain d-Asp. These results indicate that the presence of free d-Asp in marine macroalgae is restricted only to the Sargassaceae family, excluding the species in the section Teretia.

Parthenosporophytes of the brown alga Ectocarpus siliculosus exhibit sex-dependent differences in thermotolerance as well as fatty acid and sterol composition

Marine environmental research, Jan 10, 2018

In the filamentous brown alga Ectocarpus siliculosus, male and female sex is expressed during the... more In the filamentous brown alga Ectocarpus siliculosus, male and female sex is expressed during the haploid parthenosporophyte phase of the life cycle. Here, we found that male parthenosporophytes displayed thermotolerance whereas female specimens displayed severely reduced viability at 25 °C and 28 °C. Profiling of polyunsaturated fatty acids showed that n-3 and n-6 were the predominant species in male and female parthenosporophytes, respectively, and that the n-3/n-6 fatty acid ratio was not affected by a temperature change. Both male and female parthenosporophytes contained the sterols fucosterol, cholesterol, and ergosterol, but these were present at higher levels at 10-25 °C in female specimens than in males. Thus, these fatty acids and sterols would be expected to make the membranes more rigid in the female compared to the male, which is opposite to the paradigm that increased rigidity confers thermotolerance. Our results suggest that the sex-dependent thermotolerance in E. sili...

Primary Characterization of a Life-Cycle Mutant akasusabi of the Red Alga Neopyropia yezoensis

Phycology

Gametophyte-to-sporophyte transition in the haploid-diploid life cycle depends on fertilization o... more Gametophyte-to-sporophyte transition in the haploid-diploid life cycle depends on fertilization of male and female gametes. We describe here a mutant of the marine red seaweed Neopyropia yezoensis, designated akasusabi (aks), where the gametophyte-to-sporophyte transition occurs independently of fertilization. Although conchocelis filaments were produced from carpospores, severe defects in the maturation of carposporangia via mitosis to generate conchospores were observed. In the aks mutant, however, somatic cells of gametophytic thalli were able to produce conchocelis filaments without fertilization. Thus, apogamy occurs in aks. In addition, aks was highly sensitive to wounding that promotes both asexual and apogamous reproductive responses by producing spores, which develop either into blades or conchocelis filaments, indicating that aks responds to wounding by enhanced reproduction. These findings indicated that the aks mutation enables the transformation of vegetative cells to c...

Migrating Plant Cell: F-Actin Asymmetry Directed by Phosphoinositide Signaling

Polarity is a fundamental cell property essential for differentiation, proliferation and morphoge... more Polarity is a fundamental cell property essential for differentiation, proliferation and morphogenesis in unicellular and multicellular organisms. It is well known that polarized distribution of F-actin is important in providing the driving force for directional migration in mammalian leukocytes and Dictyostelium cells. Phosphoinositide (PI) signaling, including phosphatidylinositol kinases and phospholipases, is also critical for the formation of cell polarity in these cells. A monospore from the marine red alga Porphyra yezoensis is well known as a migrating plant cell and thus is a unique and useful material for investigating polarity determination in plant cells. As in leukocytes and Dictyostelium cells, monospore migration requires asymmetrical distribution of F-actin, whose establishment is regulated by the phosphatidylinositol 3-kinase and phospholipase C, whereas Koji Mikami 206 phospholipase D is involved in the maintenance of F-actin distribution. These findings indicate that the regulation of F-actin asymmetry by PI signaling cascades is evolutionarily conserved in terms of the establishment of cell polarity in migrating eukaryotic cells.

Oxidative Stress Promotes Asexual Reproduction and Apogamy in the Red Seaweed Pyropia yezoensis

Frontiers in plant science, 2017

The marine red seaweed Pyropia yezoensis has a haploid-diploid life cycle wherein two heteromorph... more The marine red seaweed Pyropia yezoensis has a haploid-diploid life cycle wherein two heteromorphic generations, a haploid gametophyte and a diploid sporophyte, are reciprocally generated from conchospores and carpospores, respectively. When we treated gametophytic blades of P. yezoensis with H2O2, discharge of asexual monospores was accelerated, resulting in increased numbers of gametophytic clones. Production of sporophytes without fertilization of male and female gametes was also observed. These findings indicate that oxidative stress can induce vegetative cells to develop into monospores that produce gametophytes asexually and can sometimes prompt carpospores to develop into sporophytes. The discovery of oxidative stress-triggered asexual reproduction and -apogamy will stimulate progress in studies of life-cycle regulation in P. yezoensis.

Photosynthesis-Dependent Extracellular Ca2+ Influx Triggers an Asexual Reproductive Cycle in the Marine Red Macroalga Porphyra yezoensis

American Journal of Plant Sciences, 2010

Asexual propagation to increase the number of gametophytic clones via the growth of asexual haplo... more Asexual propagation to increase the number of gametophytic clones via the growth of asexual haploid spores is a unique survival strategy found in marine multicellular algae. However, the mechanisms regulating the asexual life cycle are largely unknown. Here, factors involved in the regulation of production and discharge of asexual spores, so-called monospores, are identified in the marine red macroalga Porphyra yezoensis. First, enhanced discharge of monospores was found by incubation of gametophytes in ASPMT1, a modified version of the previously established synthetic medium ASP 12 . Comparison of the compositions of ASPMT1 and our standard medium, ESL, indicated that the Ca 2+ concentration in ASPMT1 was three times lower than that in ESL medium. Thus, we modified ASPMT1 by increasing its Ca 2+ concentration, resulting in reduction of monospore discharge. These findings demonstrate the role of reduced Ca 2+ concentrations in enhancing monospore production and release. Moreover, it was also observed that initiation of asexual life cycle required illumination, was repressed by DCMU, and was induced by a Ca 2+ ionophore in the dark. Taken together, these results indicate that photosynthesis-dependent Ca 2+ influx triggers the asexual life cycle by promoting the production and discharge of monospores in P.

Characterization of an eukaryotic PL-7 Alginate Lyase in the Marine Red Alga Pyropia Yezoensis

Current Biotechnology, 2015

Identification and Efficient Utilization of Antibiotics for the Development of a Stable Transformation System in Porphyra yezoensis (Bangiales, Rhodophyta)

Journal of Aquaculture Research & Development, 2011

Heterologous activation of the Porphyra tenera HSP70 promoter in Bangiophycean algal cells

Bioengineered bugs

Porphyra has attracted great attention for its biological and industrial importance. However, est... more Porphyra has attracted great attention for its biological and industrial importance. However, establishment of a stable nuclear transformation has not yet been achieved in these organisms, which impedes the molecular biological study and the development of a molecular breeding method for them. Toward establishing the stable transformation, we have recently developed an efficient transient gene expression system in Bangiophycean algae, in which the HSP70 promoter from P. tenera (PtHSP70 promoter) was activated heterologously in P. yezoensis cells. Since heterologous promoters are required for homologous recombination-based stable transformation, the identification of heterologously activated promoters is important in establishing a stable transformation system in individual Bangiophycean alga. We here examined the activation of the PtHSP70 promoter using the GC-rich PyGUS reporter system in additional Porphyra and Bangia species. The results indicated that this promoter drove express...