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Testing time: can ethanol-induced pulses of proposed oscillator components phase shift rhythms in Arabidopsis?

ABSTRACT: Circadian rhythms are generated by endogenous central oscillators that respond to input from the environment and regulate rhythmic outputs. In Arabidopsis, more than a dozen components that affect rhythms have been identified and used to propose models of the central oscillator. However, none has been shown to fulfill one of the expected characteristics of an oscillator component: that a pulse of its expression shifts the phase of circadian rhythms. Here we show that a pulse of the proposed oscillator components CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) causes dramatic phase shifts in rhythms of expression of the circadian reporter CAB2::LUC, as well as of the clock-associated genes TIMING OF CAB EXPRESSION 1 (TOC1) and GIGANTEA (GI). These results demonstrate that pulses of either CCA1 or LHY are capable of resetting the circadian clock. In contrast, a pulse of TOC1 expression did not elicit phase shifts. Control of TOC1 protein level is in part posttranscriptional; thus a pulse of TOC1 protein could be induced only at times when it is already high. Our work also shows that the ethanol-inducible system can be useful for achieving relatively short (<8 h) pulses of gene expression in seedlings.

SUBMITTER: Knowles SM

PROVIDER: S-EPMC2652257 | biostudies-literature | 2008 Dec

REPOSITORIES: biostudies-literature

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Testing time: can ethanol-induced pulses of proposed oscillator components phase shift rhythms in Arabidopsis?

Knowles Stephen M SM Lu Sheen X SX Tobin Elaine M EM

Journal of biological rhythms 20081201 6

Circadian rhythms are generated by endogenous central oscillators that respond to input from the environment and regulate rhythmic outputs. In Arabidopsis, more than a dozen components that affect rhythms have been identified and used to propose models of the central oscillator. However, none has been shown to fulfill one of the expected characteristics of an oscillator component: that a pulse of its expression shifts the phase of circadian rhythms. Here we show that a pulse of the proposed osci ...[more]

PMID: 19060255

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Project description:Molecular mechanisms responsible for 24 h circadian oscillations, entrainment to external cues, encoding of day length and the time-of-day effects have been well studied experimentally. However, it is still debated from the molecular network point of view whether each cell in suprachiasmatic nuclei harbors two molecular oscillators, where one tracks dawn and the other tracks dusk activities. A single cell dual morning and evening oscillator was proposed by Daan et al., based on the molecular network that has two sets of similar non-redundant per1/cry1 and per2/cry2 circadian genes and each can independently maintain their endogenous oscillations. Understanding of dual oscillator dynamics in a single cell at molecular level may provide insight about the circadian mechanisms that encodes day length variations and its response to external zeitgebers. We present here a realistic dual oscillator model of circadian rhythms based on the series of hypotheses proposed by Daan et al., in which they conjectured that the circadian genes per1/cry1 track dawn while per2/cry2 tracks dusk and they together constitute the morning and evening oscillators (dual oscillator). Their hypothesis also provides explanations about the encoding of day length in terms of molecular mechanisms of per/cry expression. We frame a minimal mathematical model with the assumption that per1 acts a morning oscillator and per2 acts as an evening oscillator and to support and interpret this assumption we fit the model to the experimental data of per1/per2 circadian temporal dynamics, phase response curves (PRC's), and entrainment phenomena under various light-dark conditions. We also capture different patterns of splitting phenomena by coupling two single cell dual oscillators with neuropeptides vasoactive intestinal polypeptide (VIP) and arginine vasopressin (AVP) as the coupling agents and provide interpretation for the occurrence of splitting in terms of ME oscillators, though they are not required to explain the morning and evening oscillators. The proposed dual oscillator model based on Daan's hypothesis supports per1 and per2 playing the role of morning and evening oscillators respectively and this may be the first step towards the understanding of the core molecular mechanism responsible for encoding the day length.

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Testing time: can ethanol-induced pulses of proposed oscillator components phase shift rhythms in Arabidopsis?

Publications

Testing time: can ethanol-induced pulses of proposed oscillator components phase shift rhythms in Arabidopsis?

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