Biochemical Evidence for a Timing Mechanism in
            <i>Prochlorococcus</i>

Axmann, Ilka M.; Dühring, Ulf; Seeliger, Luiza; Arnold, Anne; Vanselow, Jens T.; Kramer, Achim; Wilde, Annegret

doi:10.1128/jb.00419-09

Cited by 69 publications

(83 citation statements)

References 28 publications

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“…Admittedly, circadian rhythms have not been characterized in most of these species, although diel behaviors are widespread (22)(23)(24)(25). A reduced network that lacks kaiA and cikA has been shown to produce strong diel rhythms in the cyanobacteria Prochlorococcus marinus MED4, suggesting that CikA is indeed not necessary for daily timing (21,26). However, these rhythms are less robust than those rhythms driven by the S. elongatus clock, because they dampen quickly in constant light (27).…”

Section: Discussionmentioning

confidence: 99%

Single mutations in sasA enable a simpler Δ cikA gene network architecture with equivalent circadian properties

Shultzaberger

Boyd

Katsuki

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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The circadian input kinase of the cyanobacterium Synechococcus elongatus PCC 7942 (CikA) is important both for synchronizing circadian rhythms with external environmental cycles and for transferring temporal information between the oscillator and the global transcriptional regulator RpaA (regulator of phycobilisome-associated A). KOs of cikA result in one of the most severely altered but still rhythmic circadian phenotypes observed. We chemically mutagenized a cikA-null S. elongatus strain and screened for second-site suppressor mutations that could restore normal circadian rhythms. We identified two independent mutations in the Synechococcus adaptive sensor A (sasA) gene that produce nearly WT rhythms of gene expression, likely because they compensate for the loss of CikA on the temporal phosphorylation of RpaA. Additionally, these mutations restore the ability to reset the clock after a short dark pulse through an output-independent pathway, suggesting that SasA can influence entrainment through direct interactions with KaiC, a property previously unattributed to it. These experiments question the evolutionary advantage of integrating CikA into the cyanobacterial clock, challenge the conventional construct of separable input and output pathways, and show how easily the cell can adapt to restore phenotype in a severely compromised genetic network.gene network | cyanobacteria | evolution S econd-site suppressor mutagenesis screens have been useful in untangling the genetic components and pathways that underlie complex cellular phenotypes (1). By understanding how mutations in one gene can compensate for changes in another, we can infer how those genes interact with each other and with their encompassing genetic network. We used this approach to better understand the genetic determination of circadian rhythms in the cyanobacterium Synechococcus elongatus PCC 7942. Because the core clock genes in this species exist as single copies, suppressing mutations are not buffered by paralogs, making S. elongatus ideal for this type of mutagenic assay. Approximately 15 genes have been identified that influence the circadian phenotype to various degrees, the most important of which are the kai genes: kaiA, kaiB, and kaiC. In cyanobacteria, time is kept through the central oscillator protein KaiC, whose phosphorylation state, conformation, and ATPase activity, which are mediated by interactions with KaiA and KaiB, cycle within a 24-h period (2-4). The temporal phosphorylation of KaiC can be reconstituted in vitro by simply combining the three Kai proteins and ATP, suggesting that time is kept primarily through a posttranslational mechanism (5). Although the Kai oscillator functions relatively robustly in isolation, additional proteins are necessary to synchronize the oscillations with the environment (entrainment) through the detection of cellular and environmental cues (input pathway) and to transfer temporal information from the oscillator to circadian-dependent transcriptional regulators (output pathway). One of these prot...

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Section: Discussionmentioning

confidence: 99%

Single mutations in sasA enable a simpler Δ cikA gene network architecture with equivalent circadian properties

Shultzaberger

Boyd

Katsuki

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…For example, transcripts encoding LdpA, an input sensor to the circadian clock (Ivleva et al, 2005), were significantly less abundant following 24 h of coculture, and transcripts for KaiB, one of the central circadian clock proteins, were less abundant after 48 h (Supplementary Table S2). Prochlorococcus has only a partial circadian oscillator that likely needs to be reset daily by sunlight, and so the function of this regulatory oscillator is thought to be influenced by the cellular redox state (Axmann et al, 2009). Thus, we hypothesize that the presence of Alteromonas also impacted Prochlorococcus transcriptional regulation via inputs to the circadian regulation system, whether via impacts on the overall redox state of the cell, changes in the function of the photosynthetic electron transport system, or as a direct or indirect consequence of altering the concentration of reactive oxygen species in the culture.…”

Section: Regulation Of Transcriptional Responses To Co-culturementioning

confidence: 99%

Torn apart and reunited: impact of a heterotroph on the transcriptome of Prochlorococcus

2016

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Microbial interactions, whether direct or indirect, profoundly affect the physiology of individual cells and ultimately have the potential to shape the biogeochemistry of the Earth. For example, the growth of Prochlorococcus, the numerically dominant cyanobacterium in the oceans, can be improved by the activity of co-occurring heterotrophs. This effect has been largely attributed to the role of heterotrophs in detoxifying reactive oxygen species that Prochlorococcus, which lacks catalase, cannot. Here, we explore this phenomenon further by examining how the entire transcriptome of Prochlorococcus NATL2A changes in the presence of a naturally co-occurring heterotroph, Alteromonas macleodii MIT1002, with which it was co-cultured for years, separated and then reunited. Significant changes in the Prochlorococcus transcriptome were evident within 6 h of initiating co-culture, with groups of transcripts changing in different temporal waves. Many transcriptional changes persisted throughout the 48 h experiment, suggesting that the presence of the heterotroph affected a stable shift in Prochlorococcus physiology. These initial transcriptome changes largely corresponded to reduced stress conditions for Prochlorococcus, as inferred from the depletion of transcripts encoding DNA repair enzymes and many members of the 'high light inducible' family of stress-response proteins. Later, notable changes were seen in transcripts encoding components of the photosynthetic apparatus (particularly, an increase in PSI subunits and chlorophyll synthesis enzymes), ribosomal proteins and biosynthetic enzymes, suggesting that the introduction of the heterotroph may have induced increased production of reduced carbon compounds for export. Changes in secretion-related proteins and transporters also highlight the potential for metabolic exchange between the two strains.

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“…Инактивация kaiA полностью разрушает функцию системы kaiABC в S. elongatus PCC 7942 . Тем не менее, в некоторых исследованиях описаны суточные закономерности клеточного цикла и экспрессии генов у Prochlorococcus и высказывается предположение о существовании «внутренних часов», контролирующих эти процессы (Shalapyonok et al, 1998;Axmann et al, 2009). …”

Section: диверсификация циркадной системы цианобактерийunclassified

Evolution of the circadian clock system in cyanobacteria: a genomic perspective

Dvornyk¹

2016

Algologia

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ВведениеЦиркадные ритмы, или так называемые «внутренние часы», возникли в клетках живых организмов как основной инструмент адаптации к смене дня и ночи, вызванной вращением нашей планеты вокруг своей оси (Pittendrigh, 1993;Dunlap et al., 2004). Этот механизм контролирует свое-временную экспрессию значительной части генов в геноме.

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Biochemical Evidence for a Timing Mechanism in Prochlorococcus

Cited by 69 publications

References 28 publications

Single mutations in sasA enable a simpler Δ cikA gene network architecture with equivalent circadian properties

Single mutations in sasA enable a simpler Δ cikA gene network architecture with equivalent circadian properties

Torn apart and reunited: impact of a heterotroph on the transcriptome of Prochlorococcus

Evolution of the circadian clock system in cyanobacteria: a genomic perspective

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