BIG Regulates Dynamic Adjustment of Circadian Period in Arabidopsis thaliana.

Timothy J Hearn,Maria C Marti Ruiz,Michael J Haydon,S.M Abdul-Awal,Camilla R Stanton,Frederica L Theodoulou,Alex A.R Webb,Matthew A Hannah,Rinukshi Wimalasekera

doi:10.1104/pp.18.00571

Timothy J Hearn, Maria C Marti Ruiz + Show 7 more

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https://doi.org/10.1104/pp.18.00571

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Abstract

Circadian clocks drive rhythms with a period near 24 h, but the molecular basis of the regulation of the period of the circadian clockis poorly understood. We previously demonstrated that metabolites affect the free-running period of the circadian oscillator of Arabidopsis (Arabidopsis thaliana), with endogenous sugars acting as an accelerator and exogenous nicotinamide acting as a brake. Changes in circadian oscillator period are thought to adjust the timing of biological activities through the process of entrainment, in which the circadian oscillator becomes synchronized to rhythmic signals such as light and dark cycles as well as changes in internal metabolism. To identify the molecular components associated with the dynamic adjustment of circadian period, we performed a forward genetic screen. We identified Arabidopsis mutants that were either period insensitive to nicotinamide (sin) or period oversensitive to nicotinamide (son). We mapped son1 to BIG, a gene of unknown molecular function that was shown previously to play a role in light signaling. We found that son1 has an early entrained phase, suggesting that the dynamic alteration of circadian period contributes to the correct timing of biological events. Our data provide insight into how the dynamic period adjustment of circadian oscillators contributes to establishing a correct phase relationship with the environment and show that BIG is involved in this process.

Highlights

Circadian clocks drive rhythms with a period near 24 h, but the molecular basis of the regulation of the period of the circadian clockis poorly understood
We used the CHLOROPHYLL A/B BINDING PROTEIN2 promoter:LUCIFERASE+ (CAB2):LUC+ reporter because this had been used previously to study the effect of nicotinamide on the Arabidopsis circadian clock (Dodd et al, 2007)
By measuring the behavior of circadian clock output in CAB2, we could examine the consequence of the entire oscillator dynamics, which is not possible when measuring the behavior of a single oscillator component

Summary

Introduction

Circadian clocks drive rhythms with a period near 24 h, but the molecular basis of the regulation of the period of the circadian clockis poorly understood. Suc reduces the circadian period under dim light conditions (Haydon et al, 2013), whereas nicotinamide makes the circadian clock run more slowly, with a period near 27 h (Dodd et al, 2007). The way in which circadian clocks regulate and adjust the circadian period is unknown We refer to this ability of the circadian clock to adapt to environmental conditions as dynamic adjustment of circadian period. In Arabidopsis, circadian regulation of [Ca2+]cyt is driven by the second messenger cADP ribose (cADPR) under the control of the morning oscillator gene CIRCADIAN CLOCK ASSOCIATED1 (CCA1; Dodd et al, 2007; Xu et al, 2007). Consistent with the effect of nicotinamide on circadian period being due to the inhibition of ADPR cyclase, a knockout mutation of CD38, the main mammalian ADPR cyclase, causes a long circadian period in mice (Sahar et al, 2011)

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