GIGANTEA gates gibberellin signaling through stabilization of the DELLA proteins in Arabidopsis

Circadian clock circuitry intersects with a plethora of signaling pathways to adequately time physiological processes to occur at the most appropriate time of the day and year. However, our mechanistic understanding of how the clockwork is wired to its output is limited. Here we uncover mechanistic connections between the core clock component GIGANTEA (GI) and hormone signaling through the modulation of key components of the transduction pathways. Specifically, we show how GI modulates gibberellin (GA) signaling through the stabilization of the DELLA proteins, which act as negative components in the signaling of this hormone. GI function within the GA pathway is required to precisely time the permissive gating of GA sensitivity, thereby determining the phase of GA-regulated physiological outputs.

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EARLY FLOWERING 3 controls temperature responsiveness of the circadian clock

10.1101/2020.11.11.378307 ◽

2020 ◽

Author(s):

Zihao Zhu ◽

Marcel Quint ◽

Muhammad Usman Anwer

Keyword(s):

Circadian Clock ◽

Biological Rhythms ◽

Early Flowering ◽

Climate Change Scenarios ◽

Temperature Changes ◽

Physiological Processes ◽

Average Global Temperature ◽

Clock Component ◽

Rhythmic Growth

SummaryPredictable changes in light and temperature during a diurnal cycle are major entrainment cues that enable the circadian clock to generate internal biological rhythms that are synchronized with the external environment. With the average global temperature predicted to keep increasing, the intricate light-temperature coordination that is necessary for clock functionality is expected to be seriously affected. Hence, understanding how temperature signals are perceived by the circadian clock has become an important issue, especially in light of climate change scenarios. In Arabidopsis, the clock component EARLY FLOWERING 3 (ELF3) not only serves as an essential light Zeitnehmer, but also functions as a thermosensor participating in thermomorphogenesis. However, the role of ELF3 in temperature entrainment of the circadian clock is not fully understood. Here, we report that ELF3 is essential for delivering temperature input to the clock. We demonstrate that in the absence of ELF3, the oscillator was unable to properly respond to temperature changes, resulting in an impaired gating of thermoresponses. Consequently, clock-controlled physiological processes such as rhythmic growth and cotyledon movement were disturbed. Together, our results reveal that ELF3 is an essential Zeitnehmer for temperature sensing of the oscillator, and thereby for coordinating the rhythmic control of thermoresponsive physiological outputs.

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Achilles-Mediated and Sex-Specific Regulation of Circadian mRNA Rhythms in Drosophila

Journal of Biological Rhythms ◽

10.1177/0748730419830845 ◽

2019 ◽

Vol 34 (2) ◽

pp. 131-143 ◽

Cited By ~ 3

Author(s):

Jiajia Li ◽

Renee Yin Yu ◽

Farida Emran ◽

Brian E. Chen ◽

Michael E. Hughes

Keyword(s):

Circadian Clock ◽

Molecular Mechanisms ◽

Rna Binding ◽

Clock Genes ◽

Peripheral Tissues ◽

Knock Down ◽

Rhythmic Expression ◽

The Core ◽

Physiological Processes ◽

Specific Regulation

The circadian clock is an evolutionarily conserved mechanism that generates the rhythmic expression of downstream genes. The core circadian clock drives the expression of clock-controlled genes, which in turn play critical roles in carrying out many rhythmic physiological processes. Nevertheless, the molecular mechanisms by which clock output genes orchestrate rhythmic signals from the brain to peripheral tissues are largely unknown. Here we explored the role of one rhythmic gene, Achilles, in regulating the rhythmic transcriptome in the fly head. Achilles is a clock-controlled gene in Drosophila that encodes a putative RNA-binding protein. Achilles expression is found in neurons throughout the fly brain using fluorescence in situ hybridization (FISH), and legacy data suggest it is not expressed in core clock neurons. Together, these observations argue against a role for Achilles in regulating the core clock. To assess its impact on circadian mRNA rhythms, we performed RNA sequencing (RNAseq) to compare the rhythmic transcriptomes of control flies and those with diminished Achilles expression in all neurons. Consistent with previous studies, we observe dramatic upregulation of immune response genes upon knock-down of Achilles. Furthermore, many circadian mRNAs lose their rhythmicity in Achilles knock-down flies, suggesting that a subset of the rhythmic transcriptome is regulated either directly or indirectly by Achilles. These Achilles-mediated rhythms are observed in genes involved in immune function and in neuronal signaling, including Prosap, Nemy and Jhl-21. A comparison of RNAseq data from control flies reveals that only 42.7% of clock-controlled genes in the fly brain are rhythmic in both males and females. As mRNA rhythms of core clock genes are largely invariant between the sexes, this observation suggests that sex-specific mechanisms are an important, and heretofore under-appreciated, regulator of the rhythmic transcriptome.

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The Plant Circadian Clock and Chromatin Modifications

Genes ◽

10.3390/genes9110561 ◽

2018 ◽

Vol 9 (11) ◽

pp. 561 ◽

Cited By ~ 6

Author(s):

Ping Yang ◽

Jianhao Wang ◽

Fu-Yu Huang ◽

Songguang Yang ◽

Keqiang Wu

Keyword(s):

Circadian Clock ◽

Clock Genes ◽

Feedback Regulation ◽

Chromatin Modifications ◽

Environmental Signals ◽

The Core ◽

Physiological Processes ◽

Circadian Clock Genes ◽

Rhythmic Gene ◽

Transcriptional Feedback

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.

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Altered expression of the core circadian clock component PERIOD2 contributes to osteoarthritis-like changes in chondrocyte activity

Chronobiology International ◽

10.1080/07420528.2018.1540493 ◽

2018 ◽

Vol 36 (3) ◽

pp. 319-331 ◽

Cited By ~ 3

Author(s):

Jing Rong ◽

Mark Zhu ◽

Jacob Munro ◽

Jillian Cornish ◽

Geraldine M McCarthy ◽

...

Keyword(s):

Circadian Clock ◽

Altered Expression ◽

The Core ◽

Clock Component

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The circadian clock: a central mediator of cartilage maintenance and osteoarthritis development?

Rheumatology ◽

10.1093/rheumatology/keab197 ◽

2021 ◽

Author(s):

Raewyn C Poulsen ◽

James I Hearn ◽

Nicola Dalbeth

Keyword(s):

Circadian Clock ◽

Current Knowledge ◽

Cell Signalling ◽

The Core ◽

Tissue Degeneration ◽

Cell Tissue ◽

Clock Component ◽

Oa Chondrocytes ◽

Cell Signalling Pathway ◽

Oxidative Insult

Abstract The circadian clock is a specialized cell signalling pathway present in all cells. Loss of clock function leads to tissue degeneration and premature ageing in animal models demonstrating the fundamental importance of clocks for cell, tissue and organism health. There is now considerable evidence that the chondrocyte circadian clock is altered in OA. The purpose of this review is to summarize current knowledge regarding the nature of the change in the chondrocyte clock in OA and the implications of this change for disease development. Expression of the core clock component, BMAL1, has consistently been shown to be lower in OA chondrocytes. This may contribute to changes in chondrocyte differentiation and extracellular matrix turnover in disease. Circadian clocks are highly responsive to environmental factors. Mechanical loading, diet, inflammation and oxidative insult can all influence clock function. These factors may contribute to causing the change in the chondrocyte clock in OA.

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Molecular convergence of clock and photosensory pathways through PIF3–TOC1 interaction and co-occupancy of target promoters

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1603745113 ◽

2016 ◽

Vol 113 (17) ◽

pp. 4870-4875 ◽

Cited By ~ 54

Author(s):

Judit Soy ◽

Pablo Leivar ◽

Nahuel González-Schain ◽

Guiomar Martín ◽

Céline Diaz ◽

...

Keyword(s):

Transcription Factors ◽

Circadian Clock ◽

Transcriptional Activation ◽

Protein Abundance ◽

The Core ◽

Collective Activity ◽

Clock Component ◽

Growth Promoting ◽

Circadian Clock Output ◽

Target Promoters

A mechanism for integrating light perception and the endogenous circadian clock is central to a plant’s capacity to coordinate its growth and development with the prevailing daily light/dark cycles. Under short-day (SD) photocycles, hypocotyl elongation is maximal at dawn, being promoted by the collective activity of a quartet of transcription factors, called PIF1, PIF3, PIF4, and PIF5 (phytochrome-interacting factors). PIF protein abundance in SDs oscillates as a balance between synthesis and photoactivated-phytochrome–imposed degradation, with maximum levels accumulating at the end of the long night. Previous evidence shows that elongation under diurnal conditions (as well as in shade) is also subjected to circadian gating. However, the mechanism underlying these phenomena is incompletely understood. Here we show that the PIFs and the core clock component Timing of CAB expression 1 (TOC1) display coincident cobinding to the promoters of predawn-phased, growth-related genes under SD conditions. TOC1 interacts with the PIFs and represses their transcriptional activation activity, antagonizing PIF-induced growth. Given the dynamics of TOC1 abundance (displaying high postdusk levels that progressively decline during the long night), our data suggest that TOC1 functions to provide a direct output from the core clock that transiently constrains the growth-promoting activity of the accumulating PIFs early postdusk, thereby gating growth to predawn, when conditions for cell elongation are optimal. These findings unveil a previously unrecognized mechanism whereby a core circadian clock output signal converges immediately with the phytochrome photosensory pathway to coregulate directly the activity of the PIF transcription factors positioned at the apex of a transcriptional network that regulates a diversity of downstream morphogenic responses.

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