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Different types of cell cycle model. Modified from Bišová and Zachleder (2014); Zachleder et al. (2021); Zachleder et al. (1997). (a) classical cell cycle model of binary fission, models of binary fission found in (b) Saccharomyces cerevisiae, (c) Scenedesmus quadricauda, (d) Chlamydomonas reinhardtii, and models of multiple fission found in (e) Scenedesmus quadricauda, (f) Chlamydomonas reinhardtii, (g) Haematococcus pluvialis, (d) Parachlorella kessleri. In binary fission (a–d), single DNA replication–division sequence occurs during the cell cycle, while two or three partially overlapping DNA replication–division sequences occur within a single cell cycle in multiple fission (e–h). G1: the phase during which the threshold size of the cell is attained; CP: commitment point for cell division; pS: the prereplication phase between the commitment point and the beginning of DNA replication. S: DNA synthesis phase; G2: the phase between the termination of DNA synthesis and the start of mitosis; M: the phase during which nuclear division and cellular division occur; M': nuclear division phase; G3: the phase separating mitosis from cellular division, which is clearly visible in some algae dividing by multiple fission; C: cellular division phase. The full circles inside the cells illustrate the size and number of nuclei. Larger circles indicate a doubling or tripling of DNA. Lines in ellipsoids represent protoplast division.
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Phytoplankton play an enormously important role in ecology and serve as critical food for aquatic organisms. The phytoplankton population rapidly increases in number after continuous cell cycles. Thus, understanding the cell cycle of phytoplankton is fundamental to the aquatic ecosystem research. The eukaryotic cell cycle has been clarified; howeve...
Citations
... The cell cycle is vital for microalgae. When microalgae are in a suitable environment, cells accumulate sufficient energy and the population rapidly increases in number after one cell cycle [5]. ...
The cell cycle is the fundamental cellular process of eukaryotes. Although cell-cycle-related genes have been identified in microalgae, their cell cycle progression differs from species to species. Cell enlargement in microalgae is an essential biological trait. At the same time, there are various causes of cell enlargement, such as environmental factors, especially gene mutations. In this study, we first determined the phenotypic and biochemical characteristics of a previously obtained enlarged-cell-size mutant of Nannochloropsis oceanica, which was designated ECS. Whole-genome sequencing analysis of the insertion sites of ECS indicated that the insertion fragment is integrated inside the 5′-UTR of U/P-type cyclin CYCU1 and significantly decreases the gene expression of this cyclin. In addition, the transcriptome showed that CYCU1 is a highly expressed cyclin. Furthermore, cell cycle analysis and RT-qPCR of cell-cycle-related genes showed that ECS maintains a high proportion of 4C cells and a low proportion of 1C cells, and the expression level of CYCU1 in wild-type (WT) cells is significantly increased at the end of the light phase and the beginning of the dark phase. This means that CYCU1 is involved in cell division in the dark phase. Our results explain the reason for the larger ECS size. Mutation of CYCU1 leads to the failure of ECS to fully complete cell division in the dark phase, resulting in an enlargement of the cell size and a decrease in cell density, which is helpful to understand the function of CYCU1 in the Nannochloropsis cell cycle.
... This comparison showed that the changes of cell size and complexity of cellular content are possibly dependent on the cell cycle phase arrested by stress. The DNA content determined by flow cytometer has often been applied in phytoplankton cell cycle analysis, especially in studies on changes in the cell cycle phase in response to environmental stress (Zhao et al., 2022). In the current study, a complete cell cycle process was clearly characterized by the percentage variations of cells at different cell cycle phases (Fig. 2). ...
... However, the BMAA exposed microalgal cells did not markedly changed synchronously, and the percentage of cells at S phase slightly increased from 10 h and peaked at 12 h with about 21 % in the BMAA exposure groups. The percentages of cells at G2/M phase peaked at 12 h in the HCl and blank control treatments when they entered dark period, which was consistent with the typical cell cycle of phytoplankton (Zhao et al., 2022;Zhang et al., 2019). The results demonstrated that cells of I. galbana were arrested by BMAA at G1 phase, with only a low percentage of G1 cells completing DNA replication and mitosis processes. ...
The phycotoxin β-N-methylamino-l-alanine (BMAA) has attracted attention due to its risks to marine organisms and human health. In this study, approximately 85 % of synchronized cells of the marine microalga Isochrysis galbana were arrested at the cell cycle G1 phase by BMAA at 6.5 μM for a 24-h exposure. The concentration of chlorophyll a (Chl a) gradually decreased, while the maximum quantum yield of PSII (Fv/Fm), the maximum relative electron transport rate (rETRmax), light utilization efficiency (α) and half-saturated light irradiance (Ik) reduced early and recovered gradually in I. galbana exposed to BMAA in 96-h batch cultures. Transcriptional expression of I. galbana analyzed at 10, 12, and 16 h disclosed multiple mechanisms of BMAA to suppress the microalgal growth. Production of ammonia and glutamate was limited by the down-regulation of nitrate transporters, glutamate synthase, glutamine synthetase, cyanate hydrolase, and formamidase. Diverse extrinsic proteins related to PSII, PSI, cytochrome b6f complex, and ATPase were influenced by BMAA at transcriptional level. Suppression of the DNA replication and mismatch repair pathways increased the accumulation of misfolded proteins, which was reflected by the up-regulated expression of proteasome to accelerate proteolysis. This study improves our understanding of the chemical ecology impacts of BMAA in marine ecosystems.
... Therefore, understanding the cell cycle and regulation mechanism to achieve the appropriate biomass is essential for maintaining aquatic ecosystem health. Zhao et al. (2022) summarized the current information about the eukaryotic phytoplankton cell cycle and the environmental factors that affect it. They also introduced the research methods for the phytoplankton cell cycle, highlighted the progress in understanding the molecular mechanisms of phytoplankton cell cycle regulation, and discussed future directions for phytoplankton cell cycle research. ...
The phycotoxin dinophysistoxins are widely distributed in the global marine environments and potentially threaten marine organisms and human health. The mechanism of the dinophysistoxin toxicity in inhibiting the growth of microalgae is less well understood. In this study, effects of the dissolved dinophysistoxin-1 (DTX1) on the growth, pigment contents, PSII photosynthetic efficiency, oxidative stress response and cell cycle of the marine microalga Isochrysis galbana were investigated. Growth of I. galbana was significantly inhibited by DTX1 with 0.6-1.5 μmol L-1 in a 96-h batch culture, corresponding the 96 h-EC50 of DTX1 at 0.835 μmol L-1. The maximum quantum yield of PSII (Fv/Fm), and light utilization efficiency (α) were obviously reduced by DTX1 at 1.5 μmol L-1 during 96-h exposure. Contents of most of pigments were generally reduced by DTX1 with a dose-depend pattern in microalgal cells except for diatoxanthin. The ROS levels were increased by DTX1 with 0.6-1.5 μmol L-1 after 72-h exposure, while the contents or activities of MDA, GSH, SOD and CAT were significantly increased by DTX1 at 1.5 μmol L-1 at 96 h. The inhibitory effect of DTX1 on the growth of I. galbana was mainly caused by the production of ROS in the cells. Cell cycle analysis showed that the I. galbana cell cycle was arrested by DTX1 at G2/M phase. This study enhances the understanding of the chemical ecology effects of DTX1 on marine microalgae and also provides fundamental data for deriving water quality criteria of DSTs for marine organisms.
