GUN4 Affects the Circadian Clock and Seedlings Adaptation to Changing Light Conditions

The chloroplast is a key organelle for photosynthesis and perceiving environmental information. GENOME UNCOUPLED 4 (GUN4) has been shown to be required for the regulation of both chlorophyll synthesis, reactive oxygen species (ROS) homeostasis and plastid retrograde signaling. In this study, we found that growth of the gun4 mutant was significantly improved under medium strong light (200 μmol photons m−2s−1) compared to normal light (100 μmol photons m−2s−1), in marked contrast to wild-type (WT). Further analysis revealed that GUN4 interacts with SIGNAL RECOGNITION PARTICLE 54 KDA SUBUNIT (SRP43) and SRP54. RNA-seq analysis indicated that the expression of genes for light signaling and the circadian clock is altered in gun4 compared with (WT). qPCR analysis confirmed that the expression of the clock genes CLOCK-RELATED 1 (CCA1), LATE ELONGATION HYPOCOTYL (LHY), TIMING OF CAB EXPRESSION 1 (TOC1) and PSEUDO RESPONSE REGULATOR 7 (PRR7) is significantly changed in the gun4 and srp54 mutants under normal and medium strong light conditions. These results suggest that GUN4 may coordinate the adaptation of plants to changing light conditions by regulating the biological clock, although it is not clear whether the effect is direct or indirect.

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Chrono-pharmaceutical approaches to optimize dosing regimens based on the circadian clock machinery

Indian Journal of Pharmacy and Pharmacology ◽

10.18231/j.ijpp.2021.042 ◽

2022 ◽

Vol 8 (4) ◽

pp. 238-242

Author(s):

Shoheb S Shaikh ◽

Sachin M Kokate

Keyword(s):

Circadian Clock ◽

Biological Clock ◽

Drug Efficacy ◽

Therapeutic Index ◽

Expression Of Genes ◽

Symptom Intensity ◽

Dosing Regimens ◽

The Difference ◽

Toxicity Of Drugs ◽

And Behavior

Daily rhythmic variations in biological functions affect the efficacy and/or toxicity of drugs: a large number of drugs cannot be expected to exhibit the same potency at different administration times. The “circadian clock” is an endogenous timing system that broadly regulates metabolism, physiology and behavior. In mammals, this clock governs the oscillatory expression of the majority of genes with a period length of approximately 24 h. Genetic studies have revealed that molecular components of the circadian clock regulate the expression of genes responsible for the sensitivity to drugs and their disposition. The circadian control of pharmacodynamics and pharmacokinetics enables ‘chrono-pharmaceutical’ applications, namely drug administration at appropriate times of day to optimize the therapeutic index (efficacy vs. toxicity). On the other hand, a variety of pathological conditions also exhibit marked day-night changes in symptom intensity. Currently, novel therapeutic approaches are facilitated by the development of chemical compound targeted to key proteins that cause circadian exacerbation of disease events. This review presents an overview of the current understanding of the role of the circadian biological clock in regulating drug efficacy and disease conditions, and also describes the importance of identifying the difference in the circadian machinery between diurnal and nocturnal animals to select the most appropriate times of day to administer drugs in humans.

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Circadian control of ORE1 by PRR9 positively regulates leaf senescence in Arabidopsis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1722407115 ◽

2018 ◽

Vol 115 (33) ◽

pp. 8448-8453 ◽

Cited By ~ 38

Author(s):

Hyunmin Kim ◽

Hyo Jung Kim ◽

Quy Thi Vu ◽

Sukjoon Jung ◽

C. Robertson McClung ◽

...

Keyword(s):

Circadian Clock ◽

Leaf Senescence ◽

Posttranscriptional Regulation ◽

Clock Genes ◽

Response Regulator ◽

Early Flowering ◽

Physiological Alterations ◽

Circadian Control ◽

Age Dependent ◽

Pseudo Response Regulator

The circadian clock coordinates the daily cyclic rhythm of numerous biological processes by regulating a large portion of the transcriptome. In animals, the circadian clock is involved in aging and senescence, and circadian disruption by mutations in clock genes frequently accelerates aging. Conversely, aging alters circadian rhythmicity, which causes age-associated physiological alterations. However, interactions between the circadian clock and aging have been rarely studied in plants. Here, we investigated potential roles for the circadian clock in the regulation of leaf senescence in plants. Members of the evening complex in Arabidopsis circadian clock, EARLY FLOWERING 3 (ELF3), EARLY FLOWERING 4 (ELF4), and LUX ARRHYTHMO (LUX), as well as the morning component PSEUDO-RESPONSE REGULATOR 9 (PRR9), affect both age-dependent and dark-induced leaf senescence. The circadian clock regulates the expression of several senescence-related transcription factors. In particular, PRR9 binds directly to the promoter of the positive aging regulator ORESARA1 (ORE1) gene to promote its expression. PRR9 also represses miR164, a posttranscriptional repressor of ORE1. Consistently, genetic analysis revealed that delayed leaf senescence of a prr9 mutant was rescued by ORE1 overexpression. Thus, PRR9, a core circadian component, is a key regulator of leaf senescence via positive regulation of ORE1 through a feed-forward pathway involving posttranscriptional regulation by miR164 and direct transcriptional regulation. Our results indicate that, in plants, the circadian clock and leaf senescence are intimately interwoven as are the clock and aging in animals.

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Identification and temporal expression of putative circadian clock transcripts in the amphipod crustaceanTalitrus saltator

PeerJ ◽

10.7717/peerj.2555 ◽

2016 ◽

Vol 4 ◽

pp. e2555 ◽

Cited By ~ 12

Author(s):

Joseph F. O’Grady ◽

Laura S. Hoelters ◽

Martin T. Swain ◽

David C. Wilcockson

Keyword(s):

Circadian Clock ◽

Time Course ◽

Clock Genes ◽

Biological Clock ◽

Experimental Manipulation ◽

Sandy Beaches ◽

Sequencing Data ◽

Temporal Expression ◽

Activity Rhythms ◽

The Core

BackgroundTalitrus saltatoris an amphipod crustacean that inhabits the supralittoral zone on sandy beaches in the Northeast Atlantic and Mediterranean.T. saltatorexhibits endogenous locomotor activity rhythms and time-compensated sun and moon orientation, both of which necessitate at least one chronometric mechanism. Whilst their behaviour is well studied, currently there are no descriptions of the underlying molecular components of a biological clock in this animal, and very few in other crustacean species.MethodsWe harvested brain tissue from animals expressing robust circadian activity rhythms and used homology cloning and Illumina RNAseq approaches to sequence and identify the core circadian clock and clock-related genes in these samples. We assessed the temporal expression of these genes in time-course samples from rhythmic animals using RNAseq.ResultsWe identified a comprehensive suite of circadian clock gene homologues inT. saltatorincluding the ‘core’ clock genesperiod(Talper),cryptochrome 2(Talcry2),timeless(Taltim),clock(Talclk), andbmal1(Talbmal1). In addition we describe the sequence and putative structures of 23 clock-associated genes including two unusual, extended isoforms of pigment dispersing hormone (Talpdh). We examined time-course RNAseq expression data, derived from tissues harvested from behaviourally rhythmic animals, to reveal rhythmic expression of these genes with approximately circadian period inTalperandTalbmal1. Of the clock-related genes,casein kinase IIβ(TalckIIβ),ebony(Talebony),jetlag(Taljetlag),pigment dispensing hormone(Talpdh),protein phosphatase 1(Talpp1),shaggy(Talshaggy),sirt1(Talsirt1), sirt7 (Talsirt7) and supernumerary limbs (Talslimb) show temporal changes in expression.DiscussionWe report the sequences of principle genes that comprise the circadian clock ofT. saltatorand highlight the conserved structural and functional domains of their deduced cognate proteins. Our sequencing data contribute to the growing inventory of described comparative clocks. Expression profiling of the identified clock genes illuminates tantalising targets for experimental manipulation to elucidate the molecular and cellular control of clock-driven phenotypes in this crustacean.

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An Altered Circadian Clock Coupled with a Higher Photosynthesis Efficiency Could Explain the Better Agronomic Performance of a New Coffee Clone When Compared with a Standard Variety

International Journal of Molecular Sciences ◽

10.3390/ijms20030736 ◽

2019 ◽

Vol 20 (3) ◽

pp. 736

Author(s):

Lucile Toniutti ◽

Jean-Christophe Breitler ◽

Charlie Guittin ◽

Sylvie Doulbeau ◽

Hervé Etienne ◽

...

Keyword(s):

Electron Transport ◽

Circadian Clock ◽

Chlorophyll A ◽

Chlorophyll A Fluorescence ◽

Clock Genes ◽

Photosynthetic Electron Transport ◽

Physiological Status ◽

Fluorescence Measurement ◽

Transport Efficiency ◽

Expression Of Genes

In a context where climate change is threatening coffee productivity, the management of coffee leaf rust is a challenging issue. Major resistant genes, which have been used for many years, are systematically being overcome by pathogens. Developing healthy plants, able to defend themselves and be productive even when attacked by the pathogen, should be part of a more sustainable alternative approach. We compared one hybrid (GPFA124), selected for its good health in various environments including a reduced rust incidence, and the cv. ‘Caturra’, considered as a standard in terms of productivity and quality but highly susceptible to rust, for phenotypic variables and for the expression of genes involved in the circadian clock and in primary photosynthetic metabolism. The GPFA124 hybrid showed increased photosynthetic electron transport efficiency, better carbon partitioning, and higher chlorophyll content. A strong relationship exists between chlorophyll a fluorescence and the expression of genes related to the photosynthetic electron transport chain. We also showed an alteration of the amplitude of circadian clock genes in the clone. Our work also indicated that increased photosynthetic electron transport efficiency is related to the clone’s better performance. Chlorophyll a fluorescence measurement is a good indicator of the coffee tree’s physiological status for the breeder. We suggest a connection between the circadian clock and carbon metabolism in coffee tree.

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Changing planetary rotation rescues the biological clock mutantlhy cca1ofArabidopsis thaliana

10.1101/034629 ◽

2015 ◽

Author(s):

Andrew J. Millar ◽

Jamie T. Carrington ◽

Wei Ven Tee ◽

Sarah K. Hodge

Keyword(s):

Gene Expression ◽

Circadian Clock ◽

Double Mutant ◽

Clock Genes ◽

Biological Clock ◽

Laboratory Model ◽

Wild Type ◽

Planetary Rotation ◽

Short Period ◽

Clock Mechanism

Background: Pervasive, 24-hour rhythms from the biological clock affect diverse biological processes in metabolism and behaviour, including the human cell division cycle and sleep-wake cycle, nightly transpiration and energy balance in plants, and seasonal breeding in both plants and animals. The clock mechanism in the laboratory model plant species Arabidopsis thaliana is complex, in part due to the multiple interlocking, negative feedback loops that link the clock genes. Clock gene mutants are powerful tools to manipulate and understand the clock mechanism and its effects on physiology. The LATE ELONGATED HYPOCOTYL and CIRCADIAN CLOCK ASSOCIATED 1 genes encode dawn-expressed, Myb-related repressor proteins that delay the expression of other clock genes until late in the day. Double mutant plants (lhy cca1) have low-amplitude, short-period rhythms that have been used in multiple studies of the plant circadian clock. Results: We used in vivo imaging of several luciferase (LUC) reporter genes to test how the rhythmic gene expression of wild-type and lhy cca1 mutant plants responded to light:dark cycles. Red, blue and red+blue light were similarly able to entrain these gene expression rhythms. The timing of expression rhythms in double mutant plants showed little or no response to the duration of light under 24h light:dark cycles (dusk sensitivity), in contrast to the wild type. As the period of the mutant clock is about 18h, we tested light:dark cycles of different duration (T cycles), simulating altered rotation of planet Earth. lhy cca1 double mutants regained as much dusk sensitivity in 20h T cycles as the wild type in 24h cycles, though the phase of the rhythm in the mutants was much earlier than wild type. The severe, triple lhy cca1 gi mutants also regained dusk sensitivity in 20h cycles. The double mutant showed some dusk sensitivity under 28h cycles. lhy cca1 double mutants under 28h cycles with short photoperiods, however, had the same apparent phase as wild-type plants. Conclusion: Simulating altered planetary rotation with light:dark cycles can reveal normal circadian performance in clock mutants that have been described as arrhythmic under standard conditions. The features rescued here comprise a dynamic behaviour (apparent phase under 28h cycles) and a dynamic property (dusk sensitivity under 20h cycles). These conditional clock phenotypes indicate that parts of the clock mechanism continue to function independently of LHY and CCA1, despite the major role of these genes in wild-type plants under standard conditions. Accessibility: Most results here will be published only in this format, citable by the DOI. Data and analysis are publicly accessible on the BioDare resource (www.biodare.ed.ac.uk), as detailed in the links below. Transgenic lines are linked to Stock Centre IDs below (Table 7).

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Identification of the suprachiasmatic nucleus in birds

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.2001.280.4.r1185 ◽

2001 ◽

Vol 280 (4) ◽

pp. R1185-R1189 ◽

Cited By ~ 43

Author(s):

Takashi Yoshimura ◽

Shinobu Yasuo ◽

Yoshikazu Suzuki ◽

Eri Makino ◽

Yuki Yokota ◽

...

Keyword(s):

Locomotor Activity ◽

Circadian Rhythms ◽

Circadian Clock ◽

Suprachiasmatic Nucleus ◽

Japanese Quail ◽

Clock Genes ◽

Biological Clock ◽

Circadian Oscillators ◽

Circadian Clock Genes ◽

Dim Light

Circadian rhythms are generated by an internal biological clock. The suprachiasmatic nucleus (SCN) in the hypothalamus is known to be the dominant biological clock regulating circadian rhythms in mammals. In birds, two nuclei, the so-called medial SCN (mSCN) and the visual SCN (vSCN), have both been proposed to be the avian SCN. However, it remains an unsettled question which nuclei are homologous to the mammalian SCN. We have identified circadian clock genes in Japanese quail and demonstrated that these genes are expressed in known circadian oscillators, the pineal and the retina. Here, we report that these clock genes are expressed in the mSCN but not in the vSCN in Japanese quail, Java sparrow, chicken, and pigeon. In addition, mSCN lesions eliminated or disorganized circadian rhythms of locomotor activity under constant dim light, but did not eliminate entrainment under light-dark (LD) cycles in pigeon. However, the lesioned birds became completely arrhythmic even under LD after the pineal and the eye were removed. These results indicate that the mSCN is a circadian oscillator in birds.

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Circadian Clock Genes and the Transcriptional Architecture of the Clock Mechanism

Endocrine Abstracts ◽

10.1530/endoabs.59.pl4 ◽

2018 ◽

Cited By ~ 1

Author(s):

Joseph Takahashi

Keyword(s):

Circadian Clock ◽

Clock Genes ◽

Circadian Clock Genes ◽

Clock Mechanism

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On the photoreactivity of some hardwood species studied by their leaf characteristics

Silva Gandavensis ◽

10.21825/sg.v23i0.998 ◽

1970 ◽

Vol 23 ◽

Author(s):

M. Van Miegroet

Keyword(s):

Morphological Characteristics ◽

Vegetation Period ◽

Forest Stand ◽

Light Environment ◽

Light Radiation ◽

Light Conditions ◽

Site Factors ◽

Leaf Characteristics ◽

Single Tree ◽

Changing Light

A certain number of measurable characteristics of tree leaves (morphological characteristics, absorption of light radiation, intensity of respiration and photosynthesis) are clearly linked with the presence of physiologically active pigments in the leaves. Leaf characteristics are highly and inequally influenced by changing conditions of light environment, especially those related to light intensity, light quality and duration of the daily illumination period. These modifications do not only apply to light radiation as created under laboratory conditions, but also to light conditions ensuing from the place in the crown of a single tree, the social position of the tree in a forest stand and the site factors in general. There are also changes taking place due to the progression of the vegetation period, at the end of which all species are less tolerant or more light demanding. The reaction of the leaves towards light radiation out of different regions of the spectrum is also different. The so-called blue light radiation (λmax = 440 nm) seems to be of the greatest importance in this relation, as species react quite different to its action. The biggest variation in leaf characteristics due to changing light environment was measured for oak and beech, which both react quickly and are qualified as 'photolabile species'. No important variations occur in leaves of ash and maple, which therefore are qualified as 'photostable species'. As a consequence of variable reactions to changing light conditions, the relationships between the species are continually modified, even in such a way that their potential for dominance is not constant. The classical division into tolerant and intolerant species or classification of the species based upon the degree of light demand, is highly inaccurate and it seems preferable to speak of relative light demands and relative tolerance. All these observations and conclusions bring about a clear confirmation of the necessity to recognize the individuality of the single tree, the special character of each growth condition, the own structure of each forest stand, the specific reaction to one sided modifications of environmental factors. This is especially important for an intensive sylvicultural practice. They also prove the necessity for more physiological and biochemical research to arrive at a better understanding of growth and its mechanism. Sylviculture in fact must try to regulate, on an expanded scale, the phenomens of growth, which is the exchange, absorption and transformation of energy. A practical interpretation and regulation of fundamental laws of physiology and growth will be possible as soon as a clinical form of sylviculture is created and the adequate instrumentarium developed.

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