Silicon transporter genes of Fragilariopsis cylindrus (Bacillariophyceae) are differentially expressed during the progression of cell cycle synchronized by Si or light

Abstract

Fragilariopsis cylindrus is one of the most successful psychrophiles in the Southern Ocean. To investigate the molecular mechanism of biomineralization in this species, we attempted to synchronize F. cylindrus growth, since new cell wall formation is tightly coupled to the cell division process. Nutrient limitation analysis showed that F. cylindrus cultures rapidly stopped growing when deprived of silicate or light, while growth continued to a certain extent in the absence of nitrate. Flow cytometry analysis indicated that deprivation of either silicate or light could effectively arrest the cell cycle of this diatom species at the G1 phase, suggesting that synchrony can be established using either factor. Fluorescence labeling of new cell walls was faintly detectable as early as approximately 6 h after silicon repletion or light irradiation, and labeling was markedly intensified by 18 h. It is revealed that the synthesis of girdle bands begins before valve synthesis in this species, with active valve synthesis occurring during the G2 / M phase. Expression profiling revealed that selective member(s) of the F. cylindrus SIT genes (FcSIT) respond to silicate and light, with a different set of genes being responsive to each factor. The Si / light double depletion experiments demonstrated that expression of one FcSIT gene is possibly correlated to transition to G2 / M phase of the cell cycle, when the valve is actively formed.

Synthesis of Si/SiO2 core/shell fluorescent submicron-spheres for monitoring the accumulation of colloidal silica during the growth of diatom Chaetoceros sp.

“…Besides, a new insight of biosilicification has also been proposed by Ikeda in two steps: extracellular silica absorption and intracellular silica cell-wall deposition. The intracellular metabolism agrees with the classical theory of diatom silicification in which the absorbed SiO2(OH)2 2ions are transported to silica deposition vesicles (SDV) where the silica polymerization process and exocytosis to cell wall occur [24].The classical theory states that the extracellular silicic acids in the form of SiO2(OH)2 2ions are absorbed through the cell wall by a silicic-acid receptors (Si-receptors) [24,25]. In contrast to this, Ikeda recommended that the silicic acid in the form of Si(OH)4 formed colloidal SiO2 particles, immobilized on diatoms' surface before being absorbed into the cell [23].…”

“…The diatom growth is required silica in soluble phase [17][18][19]. As the silicate ions (SiO3 -) have been added to the media, they accumulate on the surface of the diatom and form SiO2(OH)2 2formula to become suitable for the diatom to absorb through a silica-receptor on their surface [24,25]. Therefore, the diatoms might release chemicals that can elevate the pH of the solution, as also experienced in our culturing progress in which the pH value increased from 7 to 8.5.…”

Cellular Hallmarks and Regulation of the Diatom Cell Cycle

“…However, it is clear that in contrast to animal or fungal cells where the G1/S phase checkpoint integrates both internal and external signals and the G2/M checkpoint is responsive to the internal cues, external factors influence both G1/S and G2/M checkpoints in many diatoms. Silica depletion was shown to arrest or lengthen both G1 and G2 phase duration in F. cylindrus, Thalassiosira weissflogii, and C. fusiformis, while T. pseudonana arrests predominantly in G1 (Brzezinski et al 1990;Coombs et al 1967;Darley and Volcani 1969;Oh et al 2018;Thamatrakoln and Hildebrand 2007;Vaulot et al 1986). All these diatoms also arrest their cell cycle at both G1/S and G2/M in response to light deprivation.…”

Testing the use of the silica deposition fluorescent probe PDMPO to estimate in situ growth rates of diatoms

“…However, only a handful of observations on frustule formation during cell division in diatoms have been carried out. From the available information, silicon deposition can start with the girdle bands (during the G1 phase of the cell cycle) or with new hypovalve, depending on species (Li and Volcani 1985;Hildebrand et al 2007Hildebrand et al , 2018Oh et al 2018). As long as cells with fully stained valves can be robustly estimated, the sequence in the formation of new frustules should not affect specific growth estimates with PDMPO.…”