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Plants
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Molecular and Cellular Mechanisms of the Acclimation Response in Microalgae
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Molecular and Cellular Mechanisms of the Acclimation Response in Microalgae

A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Cell Biology".

Deadline for manuscript submissions: closed (31 May 2021) | Viewed by 23845

Special Issue Editors

Prof. Dr. Tomoko Shinomura

E-Mail Website
Guest Editor
Plant Molecular and Cellular Biology Laboratory, Department of Biosciences, School of Science and Engineering, Teikyo University, 1-1 Toyosatodai, Utsunomiya, Tochigi 320-8551, Japan
Interests: plant physiology; microalgae; photomorphogenesis; photoregulation of life cycle; physiological functions of carotenoids
Dr. Shun Tamaki

E-Mail Website
Guest Editor
Microalgae Production Control Technology Laboratory, RIKEN, 230-0045 Yokohama, Japan
Interests: microalgae; stress response; redox regulation; primary and secondary metabolisms; system biology; genome editing

Special Issue Information

Dear Colleagues,

Many microalgae, which exist as single cells or as colonies of a small number of single cells, complete the entirety of their biological processes, from photosynthesis to stress responses to reproduction, "in one cell." This has long stimulated the interest of many biologists. Recent advances in the use of microalgae to produce biomass for foods, feeds and fine chemicals using solar energy require a detailed understanding of the molecular and cellular mechanisms of microalgae acclimation responses. Despite the surprising amount of information that has recently been accumulated, there are still many open questions and challenges in this fascinating area. For example, the regulation of gene expression in response to light (light–dark cycle, wavelength and intensity of light) is an important aspect of microalgae lifecycle progression which remains the subject of intense research.

Many other environmental stimuli provoke special physiological responses and assimilation of biomolecules. How do they interact with other bioactive substances and nutrients to achieve microalgae resistance?

In this Special Issue, articles (original research papers, perspectives, hypotheses, opinions, reviews, modeling approaches and methods) that focus on molecular and cellular mechanisms of the acclimation response in microalgae, including biochemistry, physiology, genes, proteins, metabolites, nutrition and environment, at all levels, comprising transcriptome, proteome, metabolome, system biology, epigenome studies, ROS interaction with nutrients and/or hormones, growth and senescence of microalgae, single cell studies, evolutionaly studies, field trials and agronomics in model microalgae, endsynbiotic and native species, are most welcome. 

Prof. Dr. Tomoko Shinomura
Dr. Shun Tamaki
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Plants is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • environmental stress
  • photosynthesis
  • photo-regulation
  • redox regulation
  • single cell analysis
  • phototaxis
  • gravitaxis
  • signaling
  • cultivation

Published Papers (7 papers)

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Research

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17 pages, 4031 KiB  
Article
Regeneration of the Eyespot and Flagellum in Euglena gracilis during Cell Division
by Kazunari Ozasa, Hyunwoong Kang, Simon Song, Shun Tamaki, Tomoko Shinomura and Mizuo Maeda
Plants 2021, 10(10), 2004; https://doi.org/10.3390/plants10102004 - 24 Sep 2021
Cited by 4 | Viewed by 2665
Abstract
Cell division of unicellular microalgae is a fascinating process of proliferation, at which whole organelles are regenerated and distributed to two new lives. We performed dynamic live cell imaging of Euglena gracilis using optical microscopy to elucidate the mechanisms involved in the regulation [...] Read more.
Cell division of unicellular microalgae is a fascinating process of proliferation, at which whole organelles are regenerated and distributed to two new lives. We performed dynamic live cell imaging of Euglena gracilis using optical microscopy to elucidate the mechanisms involved in the regulation of the eyespot and flagellum during cell division and distribution of the organelles into the two daughter cells. Single cells of the wild type (WT) and colorless SM-ZK cells were confined in a microfluidic device, and the appearance of the eyespot (stigma) and emergent flagellum was tracked in sequential video-recorded images obtained by automatic cell tracking and focusing. We examined 12 SM-ZK and 10 WT cells and deduced that the eyespot diminished in size and disappeared at an early stage of cell division and remained undetected for 26–97 min (62 min on average, 22 min in deviation). Subsequently, two small eyespots appeared and were distributed into the two daughter cells. Additionally, the emergent flagellum gradually shortened to zero-length, and two flagella emerged from the anterior ends of the daughter cells. Our observation revealed that the eyespot and flagellum of E. gracilis are degraded once in the cell division, and the carotenoids in the eyespot are also decomposed. Subsequently, the two eyespots/flagella are regenerated for distribution into daughter cells. As a logical conclusion, the two daughter cells generated from a single cell division possess the equivalent organelles and each E. gracilis cell has eternal or non-finite life span. The two newly regenerated eyespot and flagellum grow at different rates and mature at different timings in the two daughter cells, resulting in diverse cell characteristics in E. gracilis. Full article
(This article belongs to the Special Issue Molecular and Cellular Mechanisms of the Acclimation Response in Microalgae)
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12 pages, 2268 KiB  
Article
Characterization of Chlamydomonas reinhardtii Mutants That Exhibit Strong Positive Phototaxis
by Jun Morishita, Ryutaro Tokutsu, Jun Minagawa, Toru Hisabori and Ken-ichi Wakabayashi
Plants 2021, 10(7), 1483; https://doi.org/10.3390/plants10071483 - 20 Jul 2021
Cited by 4 | Viewed by 4234
Abstract
The most motile phototrophic organisms exhibit photo-induced behavioral responses (photobehavior) to inhabit better light conditions for photosynthesis. The unicellular green alga Chlamydomonas reinhardtii is an excellent model organism to study photobehavior. Several years ago, we found that C. reinhardtii cells reverse their phototactic [...] Read more.
The most motile phototrophic organisms exhibit photo-induced behavioral responses (photobehavior) to inhabit better light conditions for photosynthesis. The unicellular green alga Chlamydomonas reinhardtii is an excellent model organism to study photobehavior. Several years ago, we found that C. reinhardtii cells reverse their phototactic signs (i.e., positive and negative phototaxis) depending on the amount of reactive oxygen species (ROS) accumulated in the cell. However, its molecular mechanism is unclear. In this study, we isolated seven mutants showing positive phototaxis, even after the induction of negative phototaxis (ap1~7: always positive) to understand the ROS-dependent regulatory mechanism for the phototactic sign. We found no common feature in the mutants regarding their growth, high-light tolerance, and photosynthetic phenotypes. Interestingly, five of them grew faster than the wild type. These data suggest that the ROS-dependent regulation of the phototactic sign is not a single pathway and is affected by various cellular factors. Additionally, the isolation and analyses of mutants with defects in phototactic-sign regulation may provide clues for their application to the efficient cultivation of algae. Full article
(This article belongs to the Special Issue Molecular and Cellular Mechanisms of the Acclimation Response in Microalgae)
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14 pages, 4786 KiB  
Article
The Cell Division Cycle of Euglena gracilis Indicates That the Level of Circadian Plasticity to the External Light Regime Changes in Prolonged-Stationary Cultures
by Shota Kato and Hong Gil Nam
Plants 2021, 10(7), 1475; https://doi.org/10.3390/plants10071475 - 19 Jul 2021
Cited by 1 | Viewed by 2721
Abstract
In unicellular photosynthetic organisms, circadian rhythm is tightly linked to gating of cell cycle progression, and is entrained by light signal. As several organisms obtain a fitness advantage when the external light/dark cycle matches their endogenous period, and aging alters circadian rhythms, senescence [...] Read more.
In unicellular photosynthetic organisms, circadian rhythm is tightly linked to gating of cell cycle progression, and is entrained by light signal. As several organisms obtain a fitness advantage when the external light/dark cycle matches their endogenous period, and aging alters circadian rhythms, senescence phenotypes of the microalga Euglena gracilis of different culture ages were characterized with respect to the cell division cycle. We report here the effects of prolonged-stationary-phase conditions on the cell division cycles of E. gracilis under non-24-h light/dark cycles (T-cycles). Under T-cycles, cells established from 1-month-old and 2-month-old cultures produced lower cell concentrations after cultivation in the fresh medium than cells from 1-week-old culture. This decrease was not due to higher concentrations of dead cells in the populations, suggesting that cells of different culture ages differ in their capacity for cell division. Cells from 1-week-old cultures had a shorter circadian period of their cell division cycle under shortened T-cycles than aged cells. When algae were transferred to free-running conditions after entrainment to shortened T-cycles, the young cells showed the peak growth rate at a time corresponding to the first subjective night, but the aged cells did not. This suggests that circadian rhythms are more plastic in younger E. gracilis cells. Full article
(This article belongs to the Special Issue Molecular and Cellular Mechanisms of the Acclimation Response in Microalgae)
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14 pages, 12179 KiB  
Article
Temporal Evolution of the Gravitaxis of Euglena gracilis from a Single Cell
by Kazunari Ozasa, Hyunwoong Kang, Simon Song, Shota Kato, Tomoko Shinomura and Mizuo Maeda
Plants 2021, 10(7), 1411; https://doi.org/10.3390/plants10071411 - 09 Jul 2021
Cited by 3 | Viewed by 2053
Abstract
Gravitaxis is one of the most important issues in the growth of microalgae in the water column; it determines how easily cells receive sunlight with a comfortable intensity that is below the damaging threshold. We quantitatively investigated and analyzed the gravitaxis and cell [...] Read more.
Gravitaxis is one of the most important issues in the growth of microalgae in the water column; it determines how easily cells receive sunlight with a comfortable intensity that is below the damaging threshold. We quantitatively investigated and analyzed the gravitaxis and cell multiplication of Euglena gracilis using vertically placed microchambers containing a single cell. A temporal change in gravitaxis and cell multiplication was observed after transferring the cells to fresh culture medium for 9 days. We performed 29 individual experiments with 2.5 mm × 2.5 mm × 0.1 mm square microchambers and found that the cells showed positive, negative, and moderate gravitaxis in 8, 7, and 14 cases, respectively, after transferring to fresh culture medium. A common trend was observed for the temporal change in gravitaxis for the eight initially positive gravitaxis cases. The cells with initially positive gravitaxis showed a higher rate of cell multiplication than those with initially negative gravitaxis. We also discussed the gravitaxis mechanism of E. gracilis from the observed trend of gravitaxis change and swimming traces. In addition, bioconvection in a larger and thicker chamber was investigated at a millimeter scale and visualized. Full article
(This article belongs to the Special Issue Molecular and Cellular Mechanisms of the Acclimation Response in Microalgae)
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8 pages, 1446 KiB  
Communication
CP12 Is Involved in Protection against High Light Intensity by Suppressing the ROS Generation in Synechococcus elongatus PCC7942
by Masahiro Tamoi and Shigeru Shigeoka
Plants 2021, 10(7), 1275; https://doi.org/10.3390/plants10071275 - 23 Jun 2021
Cited by 6 | Viewed by 2490
Abstract
We previously reported that CP12 formed a complex with GAPDH and PRK and regulated the activities of these enzymes and the Calvin–Benson cycle under dark conditions as the principal regulatory system in cyanobacteria. More interestingly, we found that the cyanobacterial CP12 gene-disrupted strain [...] Read more.
We previously reported that CP12 formed a complex with GAPDH and PRK and regulated the activities of these enzymes and the Calvin–Benson cycle under dark conditions as the principal regulatory system in cyanobacteria. More interestingly, we found that the cyanobacterial CP12 gene-disrupted strain was more sensitive to photo-oxidative stresses such as under high light conditions and paraquat treatment. When a mutant strain that grew normally under low light was subjected to high light conditions, decreases in chlorophyll and photosynthetic activity were observed. Furthermore, a large amount of ROS was accumulated in the cells of the CP12 gene-disrupted strain. These data suggest that CP12 also functions under light conditions and may be involved in protection against oxidative stress by controlling the flow of electrons from Photosystem I to NADPH. Full article
(This article belongs to the Special Issue Molecular and Cellular Mechanisms of the Acclimation Response in Microalgae)
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Review

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8 pages, 517 KiB  
Review
Transcription Factor-Based Genetic Engineering in Microalgae
by Keiichi Mochdia and Shun Tamaki
Plants 2021, 10(8), 1602; https://doi.org/10.3390/plants10081602 - 04 Aug 2021
Cited by 8 | Viewed by 2507
Abstract
Sequence-specific DNA-binding transcription factors (TFs) are key components of gene regulatory networks. Advances in high-throughput sequencing have facilitated the rapid acquisition of whole genome assembly and TF repertoires in microalgal species. In this review, we summarize recent advances in gene discovery and functional [...] Read more.
Sequence-specific DNA-binding transcription factors (TFs) are key components of gene regulatory networks. Advances in high-throughput sequencing have facilitated the rapid acquisition of whole genome assembly and TF repertoires in microalgal species. In this review, we summarize recent advances in gene discovery and functional analyses, especially for transcription factors in microalgal species. Specifically, we provide examples of the genome-scale identification of transcription factors in genome-sequenced microalgal species and showcase their application in the discovery of regulators involved in various cellular functions. Herein, we highlight TF-based genetic engineering as a promising framework for designing microalgal strains for microalgal-based bioproduction. Full article
(This article belongs to the Special Issue Molecular and Cellular Mechanisms of the Acclimation Response in Microalgae)
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17 pages, 1915 KiB  
Review
Diverse Biosynthetic Pathways and Protective Functions against Environmental Stress of Antioxidants in Microalgae
by Shun Tamaki, Keiichi Mochida and Kengo Suzuki
Plants 2021, 10(6), 1250; https://doi.org/10.3390/plants10061250 - 19 Jun 2021
Cited by 35 | Viewed by 5610
Abstract
Eukaryotic microalgae have been classified into several biological divisions and have evolutionarily acquired diverse morphologies, metabolisms, and life cycles. They are naturally exposed to environmental stresses that cause oxidative damage due to reactive oxygen species accumulation. To cope with environmental stresses, microalgae contain [...] Read more.
Eukaryotic microalgae have been classified into several biological divisions and have evolutionarily acquired diverse morphologies, metabolisms, and life cycles. They are naturally exposed to environmental stresses that cause oxidative damage due to reactive oxygen species accumulation. To cope with environmental stresses, microalgae contain various antioxidants, including carotenoids, ascorbate (AsA), and glutathione (GSH). Carotenoids are hydrophobic pigments required for light harvesting, photoprotection, and phototaxis. AsA constitutes the AsA-GSH cycle together with GSH and is responsible for photooxidative stress defense. GSH contributes not only to ROS scavenging, but also to heavy metal detoxification and thiol-based redox regulation. The evolutionary diversity of microalgae influences the composition and biosynthetic pathways of these antioxidants. For example, α-carotene and its derivatives are specific to Chlorophyta, whereas diadinoxanthin and fucoxanthin are found in Heterokontophyta, Haptophyta, and Dinophyta. It has been suggested that AsA is biosynthesized via the plant pathway in Chlorophyta and Rhodophyta and via the Euglena pathway in Euglenophyta, Heterokontophyta, and Haptophyta. The GSH biosynthetic pathway is conserved in all biological kingdoms; however, Euglenophyta are able to synthesize an additional thiol antioxidant, trypanothione, using GSH as the substrate. In the present study, we reviewed and discussed the diversity of microalgal antioxidants, including recent findings. Full article
(This article belongs to the Special Issue Molecular and Cellular Mechanisms of the Acclimation Response in Microalgae)
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