Research

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11 pages, 1090 KiB

Open AccessArticle

Physiological and Genetic Dissection of Sucrose Inputs to the Arabidopsis thaliana Circadian System

by Koumis Philippou, James Ronald, Alfredo Sánchez-Villarreal, Amanda M. Davis and Seth J. Davis

Genes 2019, 10(5), 334; https://doi.org/10.3390/genes10050334 - 02 May 2019

Cited by 9 | Viewed by 3203

Circadian rhythms allow an organism to synchronize internal physiological responses to the external environment. Perception of external signals such as light and temperature are critical in the entrainment of the oscillator. However, sugar can also act as an entraining signal. In this work, [...] Read more.

Circadian rhythms allow an organism to synchronize internal physiological responses to the external environment. Perception of external signals such as light and temperature are critical in the entrainment of the oscillator. However, sugar can also act as an entraining signal. In this work, we have confirmed that sucrose accelerates the circadian period, but this observed effect is dependent on the reporter gene used. This observed response was dependent on sucrose being available during free-running conditions. If sucrose was applied during entrainment, the circadian period was only temporally accelerated, if any effect was observed at all. We also found that sucrose acts to stabilize the robustness of the circadian period under red light or blue light, in addition to its previously described role in stabilizing the robustness of rhythms in the dark. Finally, we also found that CCA1 is required for both a short- and long-term response of the circadian oscillator to sucrose, while LHY acts to attenuate the effects of sucrose on circadian period. Together, this work highlights new pathways for how sucrose could be signaling to the oscillator and reveals further functional separation of CCA1 and LHY. Full article

(This article belongs to the Special Issue Genetic Regulation of Circadian Rhythm in Plants)

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12 pages, 4354 KiB

Open AccessArticle

A Magnesium Transport Protein Related to Mammalian SLC41 and Bacterial MgtE Contributes to Circadian Timekeeping in a Unicellular Green Alga

by Helen K. Feord, Frederick E.G. Dear, Darren J. Obbard and Gerben van Ooijen

Genes 2019, 10(2), 158; https://doi.org/10.3390/genes10020158 - 19 Feb 2019

Cited by 6 | Viewed by 3214

Abstract

Circadian clocks in eukaryotes involve both transcriptional-translational feedback loops, post-translational regulation, and metabolic, non-transcriptional oscillations. We recently identified the involvement of circadian oscillations in the intracellular concentrations of magnesium ions ([Mg²⁺]_i) that were conserved in three eukaryotic kingdoms. [Mg [...] Read more.

Circadian clocks in eukaryotes involve both transcriptional-translational feedback loops, post-translational regulation, and metabolic, non-transcriptional oscillations. We recently identified the involvement of circadian oscillations in the intracellular concentrations of magnesium ions ([Mg²⁺]_i) that were conserved in three eukaryotic kingdoms. [Mg²⁺]_i in turn contributes to transcriptional clock properties of period and amplitude, and can function as a zeitgeber to define phase. However, the mechanism—or mechanisms—responsible for the generation of [Mg²⁺]_i oscillations, and whether these are functionally conserved across taxonomic groups, remain elusive. We employed the cellular clock model Ostreococcus tauri to provide a first study of an MgtE domain-containing protein in the green lineage. OtMgtE shares homology with the mammalian SLC41A1 magnesium/sodium antiporter, which has previously been implicated in maintaining clock period. Using genetic overexpression, we found that OtMgtE contributes to both timekeeping and daily changes in [Mg²⁺]_i. However, pharmacological experiments and protein sequence analyses indicated that critical differences exist between OtMgtE and either the ancestral MgtE channel or the mammalian SLC41 antiporters. We concluded that even though MgtE domain-containing proteins are only distantly related, these proteins retain a shared role in contributing to cellular timekeeping and the regulation of [Mg²⁺]_i. Full article

(This article belongs to the Special Issue Genetic Regulation of Circadian Rhythm in Plants)

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18 pages, 2825 KiB

Open AccessArticle

Transcriptome Analysis of Diurnal Gene Expression in Chinese Cabbage

by Jin A. Kim, Donghwan Shim, Shipra Kumari, Ha-eun Jung, Ki-Hong Jung, Heesu Jeong, Woe-Yeon Kim, Soo In Lee and Mi-Jeong Jeong

Genes 2019, 10(2), 130; https://doi.org/10.3390/genes10020130 - 11 Feb 2019

Cited by 12 | Viewed by 3928

Abstract

Plants have developed timing mechanisms that enable them to maintain synchrony with daily environmental events. These timing mechanisms, i.e., circadian clocks, include transcriptional/translational feedback loops that drive 24 h transcriptional rhythms, which underlie oscillations in protein abundance, thus mediating circadian rhythms of behavior, [...] Read more.

Plants have developed timing mechanisms that enable them to maintain synchrony with daily environmental events. These timing mechanisms, i.e., circadian clocks, include transcriptional/translational feedback loops that drive 24 h transcriptional rhythms, which underlie oscillations in protein abundance, thus mediating circadian rhythms of behavior, physiology, and metabolism. Circadian clock genes have been investigated in the diploid model plant Arabidopsis thaliana. Crop plants with polyploid genomes—such as Brassica species—have multiple copies of some clock-related genes. Over the last decade, numerous studies have been aimed at identifying and understanding the function of paralogous genes with conserved sequences, or those that diverged during evolution. Brassica rapa’s triplicate genomes retain sequence-level collinearity with Arabidopsis. In this study, we used RNA sequencing (RNAseq) to profile the diurnal transcriptome of Brassica rapa seedlings. We identified candidate paralogs of circadian clock-related genes and assessed their expression levels. These genes and their related traits that modulate the diurnal rhythm of gene expression contribute to the adaptation of crop cultivars. Our findings will contribute to the mechanistic study of circadian clock regulation inherent in polyploidy genome crops, which differ from those of model plants, and thus will be useful for future breeding studies using clock genes. Full article

(This article belongs to the Special Issue Genetic Regulation of Circadian Rhythm in Plants)

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18 pages, 1805 KiB

Open AccessArticle

The LNK Gene Family: At the Crossroad between Light Signaling and the Circadian Clock

by María José De Leone, Carlos Esteban Hernando, Andrés Romanowski, Mariano García-Hourquet, Daniel Careno, Joaquín Casal, Matías Rugnone, Santiago Mora-García and Marcelo Javier Yanovsky

Genes 2019, 10(1), 2; https://doi.org/10.3390/genes10010002 - 20 Dec 2018

Cited by 19 | Viewed by 5920

Abstract

Light signaling pathways interact with the circadian clock to help organisms synchronize physiological and developmental processes to periodic environmental cycles. The plant photoreceptors responsible for clock resetting have been characterized, but signaling components that link the photoreceptors to the clock remain to be [...] Read more.

Light signaling pathways interact with the circadian clock to help organisms synchronize physiological and developmental processes to periodic environmental cycles. The plant photoreceptors responsible for clock resetting have been characterized, but signaling components that link the photoreceptors to the clock remain to be identified. Members of the family of NIGHT LIGHT–INDUCIBLE AND CLOCK-REGULATED (LNK) genes play key roles linking light regulation of gene expression to the control of daily and seasonal rhythms in Arabidopsis thaliana. Particularly, LNK1 and LNK2 were shown to control circadian rhythms, photomorphogenic responses, and photoperiod-dependent flowering time. Here we analyze the role of the four members of the LNK family in Arabidopsis in these processes. We found that depletion of the closely related LNK3 and LNK4 in a lnk1;lnk2 mutant background affects circadian rhythms, but not other clock-regulated processes such as flowering time and seedling photomorphogenesis. Nevertheless, plants defective in all LNK genes (lnkQ quadruple mutants) display developmental alterations that lead to increased rosette size, biomass, and enhanced phototropic responses. Our work indicates that members of the LNK family have both distinctive and partially overlapping functions, and are an essential link to orchestrate light-regulated developmental processes. Full article

(This article belongs to the Special Issue Genetic Regulation of Circadian Rhythm in Plants)

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11 pages, 1797 KiB

Open AccessArticle

PIF-Mediated Sucrose Regulation of the Circadian Oscillator is Light Quality and Temperature Dependent

by Ekaterina Shor, Raya Potavskaya, Ayelet Kurtz, Inyup Paik, Enamul Huq and Rachel Green

Genes 2018, 9(12), 628; https://doi.org/10.3390/genes9120628 - 13 Dec 2018

Cited by 10 | Viewed by 3730

Abstract

Studies are increasingly showing that metabolic and circadian (~24 h) pathways are strongly interconnected, with the circadian system regulating the metabolic state of the cell, and metabolic products feeding back to entrain the oscillator. In plants, probably the most significant impact of the [...] Read more.

Studies are increasingly showing that metabolic and circadian (~24 h) pathways are strongly interconnected, with the circadian system regulating the metabolic state of the cell, and metabolic products feeding back to entrain the oscillator. In plants, probably the most significant impact of the circadian system on metabolism is in its reciprocal regulation of photosynthesis; however, the pathways by which this occurs are still poorly understood. We have previously shown that members of the basic helix-loop-helix (bHLH) transcription factor PHYTOCHROME INTERACTING FACTOR (PIF) family are involved in the photosynthate entrainment of the circadian oscillator. In this paper, using Arabidopsis mutants and overexpression lines, we examine how temperature and light quality affect PIF-mediated sucrose signaling to the oscillator and examine the contributions of individual PIF members. Our results also show that the quality of light is important for PIF signaling, with red and blue lights having the opposite effects, and that temperature affects PIF-mediated sucrose signaling. We propose the light sensitivity of PIF-mediated sucrose entrainment of the oscillator may be important in enabling plants to distinguish between sucrose produced de novo from photosynthesis during the day and the sucrose products of starch degradation at the end of the night. Full article

(This article belongs to the Special Issue Genetic Regulation of Circadian Rhythm in Plants)

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Review

Jump to: Research

20 pages, 1869 KiB

Open AccessReview

Beyond Transcription: Fine-Tuning of Circadian Timekeeping by Post-Transcriptional Regulation

by Julieta Lisa Mateos, Maria José De Leone, Jeanette Torchio, Marlene Reichel and Dorothee Staiger

Genes 2018, 9(12), 616; https://doi.org/10.3390/genes9120616 - 10 Dec 2018

Cited by 30 | Viewed by 5313

Abstract

The circadian clock is an important endogenous timekeeper, helping plants to prepare for the periodic changes of light and darkness in their environment. The clockwork of this molecular timer is made up of clock proteins that regulate transcription of their own genes with [...] Read more.

The circadian clock is an important endogenous timekeeper, helping plants to prepare for the periodic changes of light and darkness in their environment. The clockwork of this molecular timer is made up of clock proteins that regulate transcription of their own genes with a 24 h rhythm. Furthermore, the rhythmically expressed clock proteins regulate time-of-day dependent transcription of downstream genes, causing messenger RNA (mRNA) oscillations of a large part of the transcriptome. On top of the transcriptional regulation by the clock, circadian rhythms in mRNAs rely in large parts on post-transcriptional regulation, including alternative pre-mRNA splicing, mRNA degradation, and translational control. Here, we present recent insights into the contribution of post-transcriptional regulation to core clock function and to regulation of circadian gene expression in Arabidopsis thaliana. Full article

(This article belongs to the Special Issue Genetic Regulation of Circadian Rhythm in Plants)

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16 pages, 1306 KiB

Open AccessReview

A Functional Connection between the Circadian Clock and Hormonal Timing in Arabidopsis

by Manjul Singh and Paloma Mas

Genes 2018, 9(12), 567; https://doi.org/10.3390/genes9120567 - 23 Nov 2018

Cited by 26 | Viewed by 6922

Abstract

The rotation of the Earth entails changes in environmental conditions that pervasively influence an organism’s physiology and metabolism. An internal cellular mechanism known as the circadian clock acts as an internal timekeeper that is able to perceive the changes in environmental cues to [...] Read more.

The rotation of the Earth entails changes in environmental conditions that pervasively influence an organism’s physiology and metabolism. An internal cellular mechanism known as the circadian clock acts as an internal timekeeper that is able to perceive the changes in environmental cues to generate 24-h rhythms in synchronization with daily and seasonal fluctuations. In plants, the circadian clock function is particularly important and regulates nearly every aspect of plant growth and development as well as proper responses to stresses. The circadian clock does not function in isolation but rather interconnects with an intricate network of different pathways, including those of phytohormones. Here, we describe the interplay of the circadian clock with a subset of hormones in Arabidopsis. The molecular components directly connecting the circadian and hormone pathways are described, highlighting the biological significance of such connections in the control of growth, development, fitness, and survival. We focus on the overlapping as well as contrasting circadian and hormonal functions that together provide a glimpse on how the Arabidopsis circadian system regulates hormone function in response to endogenous and exogenous cues. Examples of feedback regulation from hormone signaling to the clock are also discussed. Full article

(This article belongs to the Special Issue Genetic Regulation of Circadian Rhythm in Plants)

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11 pages, 563 KiB

Open AccessReview

The Plant Circadian Clock and Chromatin Modifications

by Ping Yang, Jianhao Wang, Fu-Yu Huang, Songguang Yang and Keqiang Wu

Genes 2018, 9(11), 561; https://doi.org/10.3390/genes9110561 - 20 Nov 2018

Cited by 7 | Viewed by 4626

Abstract

The circadian clock is an endogenous timekeeping network that integrates environmental signals with internal cues to coordinate diverse physiological processes. The circadian function depends on the precise regulation of rhythmic gene expression at the core of the oscillators. In addition to the well-characterized [...] Read more.

The circadian clock is an endogenous timekeeping network that integrates environmental signals with internal cues to coordinate diverse physiological processes. The circadian function depends on the precise regulation of rhythmic gene expression at the core of the oscillators. In addition to the well-characterized transcriptional feedback regulation of several clock components, additional regulatory mechanisms, such as alternative splicing, regulation of protein stability, and chromatin modifications are beginning to emerge. In this review, we discuss recent findings in the regulation of the circadian clock function in Arabidopsis thaliana. The involvement of chromatin modifications in the regulation of the core circadian clock genes is also discussed. Full article

(This article belongs to the Special Issue Genetic Regulation of Circadian Rhythm in Plants)

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