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The initiation of nocturnal dormancy in Synechococcus as an active process.

Takano S, Tomita J, Sonoike K, Iwasaki H - BMC Biol. (2015)

Bottom Line: Because Synechococcus is an obligate photoautotroph, it has been generally assumed that repression of the transcription in the dark (dark repression) would be caused by a nocturnal decrease in photosynthetic activities through the reduced availability of energy (e.g. adenosine triphosphate (ATP)) needed for mRNA synthesis.By contrast, when ATP levels were decreased by the inhibition of both photosynthesis and respiration, the transcriptional repression was attenuated through inhibition of RNA degradation.Even though the level of total mRNA dramatically decreased in the dark, Synechococcus cells were still viable, and they do not need de novo transcription for their survival in the dark for at least 48 hours.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering and Biological Science, Waseda University, TWIns, Shinjuku, Tokyo, 162-8480, Japan. sou.tacano@gmail.com.

ABSTRACT

Background: Most organisms, especially photoautotrophs, alter their behaviours in response to day-night alternations adaptively because of their great reliance on light. Upon light-to-dark transition, dramatic and universal decreases in transcription level of the majority of the genes in the genome of the unicellular cyanobacterium, Synechococcus elongatus PCC 7942 are observed. Because Synechococcus is an obligate photoautotroph, it has been generally assumed that repression of the transcription in the dark (dark repression) would be caused by a nocturnal decrease in photosynthetic activities through the reduced availability of energy (e.g. adenosine triphosphate (ATP)) needed for mRNA synthesis.

Results: However, against this general assumption, we obtained evidence that the rapid and dynamic dark repression is an active process. Although the addition of photosynthesis inhibitors to cells exposed to light mimicked transcription profiles in the dark, it did not significantly affect the cellular level of ATP. By contrast, when ATP levels were decreased by the inhibition of both photosynthesis and respiration, the transcriptional repression was attenuated through inhibition of RNA degradation. This observation indicates that Synechococcus actively downregulates genome-wide transcription in the dark. Even though the level of total mRNA dramatically decreased in the dark, Synechococcus cells were still viable, and they do not need de novo transcription for their survival in the dark for at least 48 hours.

Conclusions: Dark repression appears to enable cells to enter into nocturnal dormancy as a feed-forward process, which would be advantageous for their survival under periodic nocturnal conditions.

No MeSH data available.


Related in: MedlinePlus

Requirement of ATP maintenance for transcription in representative dark repressed or induced genes under dark conditions. a Loss of ATP recovery in the dark resulting from the respiratory electron transport inhibitor, DBMIB or the inhibitor of cytochrome c oxidase, KCN. We analysed and represented data as shown similarly in Fig. 1e. b Temporal expression profiles of representative dark repressed or induced genes obtained from three independent northern hybridisation analyses when DBMIB was used as the inhibitor of respiration. c Attenuated dark-induced transcriptional changes for representative dark repressed or induced genes when the cells were treated with KCN for the inhibition of respiration. Each plot shows the results of two independent northern blot analyses. For panels b and c, data representation is consistent with that in Fig. 1aDBMIB 2,5-dibromo-3-methyl-6-isopropylbenzoquinone
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Fig2: Requirement of ATP maintenance for transcription in representative dark repressed or induced genes under dark conditions. a Loss of ATP recovery in the dark resulting from the respiratory electron transport inhibitor, DBMIB or the inhibitor of cytochrome c oxidase, KCN. We analysed and represented data as shown similarly in Fig. 1e. b Temporal expression profiles of representative dark repressed or induced genes obtained from three independent northern hybridisation analyses when DBMIB was used as the inhibitor of respiration. c Attenuated dark-induced transcriptional changes for representative dark repressed or induced genes when the cells were treated with KCN for the inhibition of respiration. Each plot shows the results of two independent northern blot analyses. For panels b and c, data representation is consistent with that in Fig. 1aDBMIB 2,5-dibromo-3-methyl-6-isopropylbenzoquinone

Mentions: Among various intracellular changes upon dark acclimation, dramatic reduction of ATP could be a major trigger of dark-induced transcriptional repression. The stronger suppressive effect of DBMIB on mRNA level than that of DCMU is also consistent with this possibility, because the inhibition of both linear and cyclic electron flows with DBMIB would result in greater effects on ATP synthesis than inhibiting linear electron flow with DCMU alone (see Additional file 1: Figure S1A). Rust et al. [5] reported that the ratio ATP/(ATP + ADP) was reduced within several hours in the dark after transfer from light; however, it did not change much after incubation in the dark for one hour, while the same group more recently reported that it was reduced up to about 60–70 % of that in the light within one hour in the dark under a different illumination schedule with lower light intensity [11]. Therefore, we checked the change of ATP content under our experimental conditions upon light-to-dark transition in more detail using an ATP-luciferase assay. After cells were transferred to the dark, their ATP level transiently decreased, reaching about 30 % of that under illumination, while it rapidly recovered up to 80–90 % within 10 minutes. This level was maintained for at least for one hour (Figs. 1e and 2a, black lines). Note that maintaining about 80–90 % of the ATP content at one hour after dark acclimation is consistent with findings by Rust et al. [5]. We interpreted this recovery as the energy supply from respiratory electron transfer in the dark because some studies of ATP synthesis in cyanobacteria indicated that ATP synthesis in the dark must primarily rely on respiration (e.g. [12–16]). Consistent with this assumption, addition of DBMIB or KCN, inhibitors of respiratory electron transport [16], inhibits the recovery of ATP levels in the dark (Fig. 2a, purple and green lines).Fig. 2


The initiation of nocturnal dormancy in Synechococcus as an active process.

Takano S, Tomita J, Sonoike K, Iwasaki H - BMC Biol. (2015)

Requirement of ATP maintenance for transcription in representative dark repressed or induced genes under dark conditions. a Loss of ATP recovery in the dark resulting from the respiratory electron transport inhibitor, DBMIB or the inhibitor of cytochrome c oxidase, KCN. We analysed and represented data as shown similarly in Fig. 1e. b Temporal expression profiles of representative dark repressed or induced genes obtained from three independent northern hybridisation analyses when DBMIB was used as the inhibitor of respiration. c Attenuated dark-induced transcriptional changes for representative dark repressed or induced genes when the cells were treated with KCN for the inhibition of respiration. Each plot shows the results of two independent northern blot analyses. For panels b and c, data representation is consistent with that in Fig. 1aDBMIB 2,5-dibromo-3-methyl-6-isopropylbenzoquinone
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4494158&req=5

Fig2: Requirement of ATP maintenance for transcription in representative dark repressed or induced genes under dark conditions. a Loss of ATP recovery in the dark resulting from the respiratory electron transport inhibitor, DBMIB or the inhibitor of cytochrome c oxidase, KCN. We analysed and represented data as shown similarly in Fig. 1e. b Temporal expression profiles of representative dark repressed or induced genes obtained from three independent northern hybridisation analyses when DBMIB was used as the inhibitor of respiration. c Attenuated dark-induced transcriptional changes for representative dark repressed or induced genes when the cells were treated with KCN for the inhibition of respiration. Each plot shows the results of two independent northern blot analyses. For panels b and c, data representation is consistent with that in Fig. 1aDBMIB 2,5-dibromo-3-methyl-6-isopropylbenzoquinone
Mentions: Among various intracellular changes upon dark acclimation, dramatic reduction of ATP could be a major trigger of dark-induced transcriptional repression. The stronger suppressive effect of DBMIB on mRNA level than that of DCMU is also consistent with this possibility, because the inhibition of both linear and cyclic electron flows with DBMIB would result in greater effects on ATP synthesis than inhibiting linear electron flow with DCMU alone (see Additional file 1: Figure S1A). Rust et al. [5] reported that the ratio ATP/(ATP + ADP) was reduced within several hours in the dark after transfer from light; however, it did not change much after incubation in the dark for one hour, while the same group more recently reported that it was reduced up to about 60–70 % of that in the light within one hour in the dark under a different illumination schedule with lower light intensity [11]. Therefore, we checked the change of ATP content under our experimental conditions upon light-to-dark transition in more detail using an ATP-luciferase assay. After cells were transferred to the dark, their ATP level transiently decreased, reaching about 30 % of that under illumination, while it rapidly recovered up to 80–90 % within 10 minutes. This level was maintained for at least for one hour (Figs. 1e and 2a, black lines). Note that maintaining about 80–90 % of the ATP content at one hour after dark acclimation is consistent with findings by Rust et al. [5]. We interpreted this recovery as the energy supply from respiratory electron transfer in the dark because some studies of ATP synthesis in cyanobacteria indicated that ATP synthesis in the dark must primarily rely on respiration (e.g. [12–16]). Consistent with this assumption, addition of DBMIB or KCN, inhibitors of respiratory electron transport [16], inhibits the recovery of ATP levels in the dark (Fig. 2a, purple and green lines).Fig. 2

Bottom Line: Because Synechococcus is an obligate photoautotroph, it has been generally assumed that repression of the transcription in the dark (dark repression) would be caused by a nocturnal decrease in photosynthetic activities through the reduced availability of energy (e.g. adenosine triphosphate (ATP)) needed for mRNA synthesis.By contrast, when ATP levels were decreased by the inhibition of both photosynthesis and respiration, the transcriptional repression was attenuated through inhibition of RNA degradation.Even though the level of total mRNA dramatically decreased in the dark, Synechococcus cells were still viable, and they do not need de novo transcription for their survival in the dark for at least 48 hours.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering and Biological Science, Waseda University, TWIns, Shinjuku, Tokyo, 162-8480, Japan. sou.tacano@gmail.com.

ABSTRACT

Background: Most organisms, especially photoautotrophs, alter their behaviours in response to day-night alternations adaptively because of their great reliance on light. Upon light-to-dark transition, dramatic and universal decreases in transcription level of the majority of the genes in the genome of the unicellular cyanobacterium, Synechococcus elongatus PCC 7942 are observed. Because Synechococcus is an obligate photoautotroph, it has been generally assumed that repression of the transcription in the dark (dark repression) would be caused by a nocturnal decrease in photosynthetic activities through the reduced availability of energy (e.g. adenosine triphosphate (ATP)) needed for mRNA synthesis.

Results: However, against this general assumption, we obtained evidence that the rapid and dynamic dark repression is an active process. Although the addition of photosynthesis inhibitors to cells exposed to light mimicked transcription profiles in the dark, it did not significantly affect the cellular level of ATP. By contrast, when ATP levels were decreased by the inhibition of both photosynthesis and respiration, the transcriptional repression was attenuated through inhibition of RNA degradation. This observation indicates that Synechococcus actively downregulates genome-wide transcription in the dark. Even though the level of total mRNA dramatically decreased in the dark, Synechococcus cells were still viable, and they do not need de novo transcription for their survival in the dark for at least 48 hours.

Conclusions: Dark repression appears to enable cells to enter into nocturnal dormancy as a feed-forward process, which would be advantageous for their survival under periodic nocturnal conditions.

No MeSH data available.


Related in: MedlinePlus