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Li J, Qiu JX, Zeng QH, Zhang N, Xu SX, Jin J, Dong ZC, Chen L, Huang W. OsTOC1 plays dual roles in the regulation of plant circadian clock by functioning as a direct transcription activator or repressor. Cell Rep 2023; 42:112765. [PMID: 37421622 DOI: 10.1016/j.celrep.2023.112765] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 04/28/2023] [Accepted: 06/22/2023] [Indexed: 07/10/2023] Open
Abstract
Plant clock function relies on precise timing of gene expression through complex regulatory networks consisting of activators and repressors at the core of oscillators. Although TIMING OF CAB EXPRESSION 1 (TOC1) has been recognized as a repressor involved in shaping oscillations and regulating clock-driven processes, its potential to directly activate gene expression remains unclear. In this study, we find that OsTOC1 primarily acts as a transcriptional repressor for core clock components, including OsLHY and OsGI. Here, we show that OsTOC1 possesses the ability to directly activate the expression of circadian target genes. Through binding to the promoters of OsTGAL3a/b, transient activation of OsTOC1 induces the expression of OsTGAL3a/b, indicating its role as an activator contributing to pathogen resistance. Moreover, TOC1 participates in regulating multiple yield-related traits in rice. These findings suggest that TOC1's function as a transcriptional repressor is not inherent, providing flexibility to circadian regulations, particularly in outputs.
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Affiliation(s)
- Jing Li
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Sciences, South China Agricultural University, Guangzhou 510642, Guangdong, China
| | - Jia-Xin Qiu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Sciences, South China Agricultural University, Guangzhou 510642, Guangdong, China
| | - Qing-Hua Zeng
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Sciences, South China Agricultural University, Guangzhou 510642, Guangdong, China
| | - Ning Zhang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Sciences, South China Agricultural University, Guangzhou 510642, Guangdong, China
| | - Shu-Xuan Xu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Sciences, South China Agricultural University, Guangzhou 510642, Guangdong, China
| | - Jian Jin
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning 530005, China
| | - Zhi-Cheng Dong
- Guangdong Provincial Key Laboratory of Plant Adaptation and Molecular Design, Guangzhou Key Laboratory of Crop Gene Editing, Innovative Center of Molecular Genetics and Evolution, School of Life Sciences, Guangzhou University, Guangzhou 510006, China
| | - Liang Chen
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Sciences, South China Agricultural University, Guangzhou 510642, Guangdong, China; Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou 510642, Guangdong, China; Guangdong Provincial Key Laboratory of Protein Function and Regulation in Agricultural Organisms, College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
| | - Wei Huang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Sciences, South China Agricultural University, Guangzhou 510642, Guangdong, China; Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou 510642, Guangdong, China; Guangdong Provincial Key Laboratory of Protein Function and Regulation in Agricultural Organisms, College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
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Central clock components modulate plant shade avoidance by directly repressing transcriptional activation activity of PIF proteins. Proc Natl Acad Sci U S A 2020; 117:3261-3269. [PMID: 31988133 DOI: 10.1073/pnas.1918317117] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Light-environment signals, sensed by plant phytochrome photoreceptors, are transduced to target genes through direct regulation of PHYTOCHROME-INTERACTING FACTOR (PIF) transcription factor abundance and activity. Previous genome-wide DNA-binding and expression analysis has identified a set of genes that are direct targets of PIF transcriptional regulation. However, quantitative analysis of promoter occupancy versus expression level has suggested that unknown "trans factors" modulate the intrinsic transcriptional activation activity of DNA-bound PIF proteins. Here, using computational analysis of published data, we have identified PSEUDO-RESPONSE REGULATORS (PRR5 and PRR7) as displaying a high frequency of colocalization with the PIF proteins at their binding sites in the promoters of PIF Direct Target Genes (DTGs). We show that the PRRs function to suppress PIF-stimulated growth in the light and vegetative shade and that they repress the rapid PIF-induced expression of PIF-DTGs triggered by exposure to shade. The repressive action of the PRRs on both growth and DTG expression requires the PIFs, indicating direct action on PIF activity, rather than a parallel antagonistic pathway. Protein interaction assays indicate that the PRRs exert their repressive activity by binding directly to the PIF proteins in the nucleus. These findings support the conclusion that the PRRs function as direct outputs from the core circadian oscillator to regulate the expression of PIF-DTGs through modulation of PIF transcriptional activation activity, thus expanding the roles of the multifunctional PIF-signaling hub.
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Abstract
Circadian rhythms in transcription ultimately result in oscillations of key biological processes. Understanding how transcriptional rhythms are generated in plants provides an opportunity for fine-tuning growth, development, and responses to the environment. Here, we present a succinct description of the plant circadian clock, briefly reviewing a number of recent studies but mostly emphasizing the components and mechanisms connecting chromatin remodeling with transcriptional regulation by the clock. The possibility that intergenomic interactions govern hybrid vigor through epigenetic changes at clock loci and the function of epialleles controlling clock output traits during crop domestication are also discussed.
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Affiliation(s)
- Z Jeffrey Chen
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX, 78712, USA.,Department of Integrative Biology, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Paloma Mas
- Center for Research in Agricultural Genomics (CRAG), Consortium CSIC-IRTA-UAB-UB, Campus UAB, Bellaterra, 08193, Barcelona, Spain. .,Consejo Superior de Investigaciones Científicas, 08028, Barcelona, Spain.
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de Leone MJ, Hernando CE, Romanowski A, García-Hourquet M, Careno D, Casal J, Rugnone M, Mora-García S, Yanovsky MJ. The LNK Gene Family: At the Crossroad between Light Signaling and the Circadian Clock. Genes (Basel) 2018; 10:genes10010002. [PMID: 30577529 PMCID: PMC6356500 DOI: 10.3390/genes10010002] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Revised: 12/13/2018] [Accepted: 12/17/2018] [Indexed: 12/30/2022] Open
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 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.
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Affiliation(s)
- María José de Leone
- Leloir Institute, Biochemical Research Institute of Buenos Aires (IIBBA)⁻ National Scientific and Technical Research Council (CONICET), Av. Patricias Argentinas 435, Ciudad de Buenos Aires C1405BWE, Argentina.
| | - Carlos Esteban Hernando
- Leloir Institute, Biochemical Research Institute of Buenos Aires (IIBBA)⁻ National Scientific and Technical Research Council (CONICET), Av. Patricias Argentinas 435, Ciudad de Buenos Aires C1405BWE, Argentina.
| | - Andrés Romanowski
- Leloir Institute, Biochemical Research Institute of Buenos Aires (IIBBA)⁻ National Scientific and Technical Research Council (CONICET), Av. Patricias Argentinas 435, Ciudad de Buenos Aires C1405BWE, Argentina.
| | - Mariano García-Hourquet
- Leloir Institute, Biochemical Research Institute of Buenos Aires (IIBBA)⁻ National Scientific and Technical Research Council (CONICET), Av. Patricias Argentinas 435, Ciudad de Buenos Aires C1405BWE, Argentina.
| | - Daniel Careno
- Leloir Institute, Biochemical Research Institute of Buenos Aires (IIBBA)⁻ National Scientific and Technical Research Council (CONICET), Av. Patricias Argentinas 435, Ciudad de Buenos Aires C1405BWE, Argentina.
| | - Joaquín Casal
- Leloir Institute, Biochemical Research Institute of Buenos Aires (IIBBA)⁻ National Scientific and Technical Research Council (CONICET), Av. Patricias Argentinas 435, Ciudad de Buenos Aires C1405BWE, Argentina.
| | - Matías Rugnone
- The Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, USA.
| | - Santiago Mora-García
- Leloir Institute, Biochemical Research Institute of Buenos Aires (IIBBA)⁻ National Scientific and Technical Research Council (CONICET), Av. Patricias Argentinas 435, Ciudad de Buenos Aires C1405BWE, Argentina.
| | - Marcelo Javier Yanovsky
- Leloir Institute, Biochemical Research Institute of Buenos Aires (IIBBA)⁻ National Scientific and Technical Research Council (CONICET), Av. Patricias Argentinas 435, Ciudad de Buenos Aires C1405BWE, Argentina.
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Wu JF, Tsai HL, Joanito I, Wu YC, Chang CW, Li YH, Wang Y, Hong JC, Chu JW, Hsu CP, Wu SH. LWD-TCP complex activates the morning gene CCA1 in Arabidopsis. Nat Commun 2016; 7:13181. [PMID: 27734958 PMCID: PMC5065627 DOI: 10.1038/ncomms13181] [Citation(s) in RCA: 97] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 09/09/2016] [Indexed: 12/31/2022] Open
Abstract
A double-negative feedback loop formed by the morning genes CIRCADIAN CLOCK ASSOCIATED1 (CCA1)/LATE ELONGATED HYPOCOTYL (LHY) and the evening gene TIMING OF CAB EXPRESSION1 (TOC1) contributes to regulation of the circadian clock in Arabidopsis. A 24-h circadian cycle starts with the peak expression of CCA1 at dawn. Although CCA1 is targeted by multiple transcriptional repressors, including PSEUDO-RESPONSE REGULATOR9 (PRR9), PRR7, PRR5 and CCA1 HIKING EXPEDITION (CHE), activators of CCA1 remain elusive. Here we use mathematical modelling to infer a co-activator role for LIGHT-REGULATED WD1 (LWD1) in CCA1 expression. We show that the TEOSINTE BRANCHED 1-CYCLOIDEA-PCF20 (TCP20) and TCP22 proteins act as LWD-interacting transcriptional activators. The concomitant binding of LWD1 and TCP20/TCP22 to the TCP-binding site in the CCA1 promoter activates CCA1. Our study reveals activators of the morning gene CCA1 and provides an action mechanism that ensures elevated expression of CCA1 at dawn to sustain a robust clock.
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Affiliation(s)
- Jing-Fen Wu
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan
| | - Huang-Lung Tsai
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan
| | - Ignasius Joanito
- Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan
- Department of Biological Science and Technology, National Chiao Tung University, Hsinchu 300, Taiwan
- Bioinformatics Program, Taiwan International Graduate Program, Academia Sinica, Taipei 115, Taiwan
- Institute of Bioinformatics and System Biology, National Chiao Tung University, Hsinchu 300, Taiwan
| | - Yi-Chen Wu
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan
| | - Chin-Wen Chang
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan
| | - Yi-Hang Li
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan
| | - Ying Wang
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan
| | - Jong Chan Hong
- Division of Life Science, Applied Life Science (BK21 Plus Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju 660-701, Korea
- Division of Plant Sciences, University of Missouri, Columbia, South Carolina MO 65211-7310, USA
| | - Jhih-Wei Chu
- Department of Biological Science and Technology, National Chiao Tung University, Hsinchu 300, Taiwan
- Bioinformatics Program, Taiwan International Graduate Program, Academia Sinica, Taipei 115, Taiwan
- Institute of Bioinformatics and System Biology, National Chiao Tung University, Hsinchu 300, Taiwan
| | - Chao-Ping Hsu
- Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan
- Genome and Systems Biology Degree Program, National Taiwan University, Taipei 106, Taiwan
| | - Shu-Hsing Wu
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan
- Genome and Systems Biology Degree Program, National Taiwan University, Taipei 106, Taiwan
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Hernando CE, Romanowski A, Yanovsky MJ. Transcriptional and post-transcriptional control of the plant circadian gene regulatory network. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2016; 1860:84-94. [PMID: 27412912 DOI: 10.1016/j.bbagrm.2016.07.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Revised: 06/30/2016] [Accepted: 07/03/2016] [Indexed: 11/16/2022]
Abstract
The circadian clock drives rhythms in multiple physiological processes allowing plants to anticipate and adjust to periodic changes in environmental conditions. These physiological rhythms are associated with robust oscillations in the expression of thousands of genes linked to the control of photosynthesis, cell elongation, biotic and abiotic stress responses, developmental processes such as flowering, and the clock itself. Given its pervasive effects on plant physiology, it is not surprising that circadian clock genes have played an important role in the domestication of crop plants and in the improvement of crop productivity. Therefore, identifying the principles governing the dynamics of the circadian gene regulatory network in plants could strongly contribute to further speed up crop improvement. Here we provide an historical as well as a current description of our knowledge of the molecular mechanisms underlying circadian rhythms in plants. This work focuses on the transcriptional and post-transcriptional regulatory layers that control the very core of the circadian clock, and some of its complex interactions with signaling pathways that help synchronize plant growth and development to daily and seasonal changes in the environment. This article is part of a Special Issue entitled: Plant Gene Regulatory Mechanisms and Networks, edited by Dr. Erich Grotewold and Dr. Nathan Springer.
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Affiliation(s)
- C Esteban Hernando
- Fundación Instituto Leloir, Instituto de Investigaciones Bioquímicas de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina, Av. Patricias Argentinas 435, C1405BWE Ciudad de Buenos Aires, Argentina.
| | - Andrés Romanowski
- Fundación Instituto Leloir, Instituto de Investigaciones Bioquímicas de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina, Av. Patricias Argentinas 435, C1405BWE Ciudad de Buenos Aires, Argentina.
| | - Marcelo J Yanovsky
- Fundación Instituto Leloir, Instituto de Investigaciones Bioquímicas de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina, Av. Patricias Argentinas 435, C1405BWE Ciudad de Buenos Aires, Argentina.
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7
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Foo M, Somers DE, Kim PJ. Kernel Architecture of the Genetic Circuitry of the Arabidopsis Circadian System. PLoS Comput Biol 2016; 12:e1004748. [PMID: 26828650 PMCID: PMC4734688 DOI: 10.1371/journal.pcbi.1004748] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Accepted: 01/11/2016] [Indexed: 02/03/2023] Open
Abstract
A wide range of organisms features molecular machines, circadian clocks, which generate endogenous oscillations with ~24 h periodicity and thereby synchronize biological processes to diurnal environmental fluctuations. Recently, it has become clear that plants harbor more complex gene regulatory circuits within the core circadian clocks than other organisms, inspiring a fundamental question: are all these regulatory interactions between clock genes equally crucial for the establishment and maintenance of circadian rhythms? Our mechanistic simulation for Arabidopsis thaliana demonstrates that at least half of the total regulatory interactions must be present to express the circadian molecular profiles observed in wild-type plants. A set of those essential interactions is called herein a kernel of the circadian system. The kernel structure unbiasedly reveals four interlocked negative feedback loops contributing to circadian rhythms, and three feedback loops among them drive the autonomous oscillation itself. Strikingly, the kernel structure, as well as the whole clock circuitry, is overwhelmingly composed of inhibitory, rather than activating, interactions between genes. We found that this tendency underlies plant circadian molecular profiles which often exhibit sharply-shaped, cuspidate waveforms. Through the generation of these cuspidate profiles, inhibitory interactions may facilitate the global coordination of temporally-distant clock events that are markedly peaked at very specific times of day. Our systematic approach resulting in experimentally-testable predictions provides insights into a design principle of biological clockwork, with implications for synthetic biology.
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Affiliation(s)
- Mathias Foo
- Asia Pacific Center for Theoretical Physics, Pohang, Gyeongbuk, Republic of Korea
- School of Engineering, University of Warwick, Coventry, United Kingdom
| | - David E. Somers
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
| | - Pan-Jun Kim
- Asia Pacific Center for Theoretical Physics, Pohang, Gyeongbuk, Republic of Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, Gyeongbuk, Republic of Korea
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8
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Fogelmark K, Troein C. Rethinking transcriptional activation in the Arabidopsis circadian clock. PLoS Comput Biol 2014; 10:e1003705. [PMID: 25033214 PMCID: PMC4102396 DOI: 10.1371/journal.pcbi.1003705] [Citation(s) in RCA: 94] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Accepted: 05/19/2014] [Indexed: 12/19/2022] Open
Abstract
Circadian clocks are biological timekeepers that allow living cells to time their activity in anticipation of predictable daily changes in light and other environmental factors. The complexity of the circadian clock in higher plants makes it difficult to understand the role of individual genes or molecular interactions, and mathematical modelling has been useful in guiding clock research in model organisms such as Arabidopsis thaliana. We present a model of the circadian clock in Arabidopsis, based on a large corpus of published time course data. It appears from experimental evidence in the literature that most interactions in the clock are repressive. Hence, we remove all transcriptional activation found in previous models of this system, and instead extend the system by including two new components, the morning-expressed activator RVE8 and the nightly repressor/activator NOX. Our modelling results demonstrate that the clock does not need a large number of activators in order to reproduce the observed gene expression patterns. For example, the sequential expression of the PRR genes does not require the genes to be connected as a series of activators. In the presented model, transcriptional activation is exclusively the task of RVE8. Predictions of how strongly RVE8 affects its targets are found to agree with earlier interpretations of the experimental data, but generally we find that the many negative feedbacks in the system should discourage intuitive interpretations of mutant phenotypes. The dynamics of the clock are difficult to predict without mathematical modelling, and the clock is better viewed as a tangled web than as a series of loops. Like most living organisms, plants are dependent on sunlight, and evolution has endowed them with an internal clock by which they can predict sunrise and sunset. The clock consists of many genes that control each other in a complex network, leading to daily oscillations in protein levels. The interactions between genes can be positive or negative, causing target genes to be turned on or off. By constructing mathematical models that incorporate our knowledge of this network, we can interpret experimental data by comparing with results from the models. Any discrepancy between experimental data and model predictions will highlight where we are lacking in understanding. We compiled more than 800 sets of measured data from published articles about the clock in the model organism thale cress (Arabidopsis thaliana). Using these data, we constructed a mathematical model which compares favourably with previous models for simulating the clock. We used our model to investigate the role of positive interactions between genes, whether they are necessary for the function of the clock and if they can be identified in the model.
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Affiliation(s)
- Karl Fogelmark
- Computational Biology and Biological Physics, Department of Astronomy and Theoretical Physics, Lund University, Lund, Sweden
| | - Carl Troein
- Computational Biology and Biological Physics, Department of Astronomy and Theoretical Physics, Lund University, Lund, Sweden
- * E-mail:
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McClung CR. Wheels within wheels: new transcriptional feedback loops in the Arabidopsis circadian clock. F1000PRIME REPORTS 2014; 6:2. [PMID: 24592314 PMCID: PMC3883422 DOI: 10.12703/p6-2] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The circadian clock allows organisms to temporally coordinate their biology with the diurnal oscillation of the environment, which enhances plant performance. Accordingly, a fuller understanding of the circadian clock mechanism may contribute to efforts to optimize plant performance. One recurring theme in clock mechanism is coupled transcription-translation feedback loops. To date, the majority of plant transcription factors constituting these loops, including the central oscillator components CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), and TIMING OF CAB2 EXPRESSION 1 (TOC1), and the related PSEUDO-RESPONSE REGULATORS (PRRs), are transcriptional repressors, leading to a model of the clock emphasizing repressive interactions. Recent work, however, has revealed that a subset of the REVEILLE (RVE) family of Myb transcription factors closely related to CCA1 and LHY are transcriptional activators in novel feedback transcription-translation feedback loops. Other recently identified transcriptional activators that contribute to clock function include LIGHT-REGULATED WD 1 (LWD1) and LWD2 and night light-inducible and clock-regulated transcription factors NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED1 (LNK1) and LNK2. Collectively, these advances permit a substantial reconfiguration of the clock model.
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Transcriptional corepressor TOPLESS complexes with pseudoresponse regulator proteins and histone deacetylases to regulate circadian transcription. Proc Natl Acad Sci U S A 2012; 110:761-6. [PMID: 23267111 DOI: 10.1073/pnas.1215010110] [Citation(s) in RCA: 186] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Circadian clocks are ubiquitous molecular time-keeping mechanisms that coordinate physiology and metabolism and provide an adaptive advantage to higher plants. The central oscillator of the plant clock is composed of interlocked feedback loops that involve multiple repressive factors acting throughout the circadian cycle. Pseudo response regulators (PRRs) comprise a five-member family that is essential to the function of the central oscillator. PRR5, PRR7, and PRR9 can bind the promoters of the core clock genes circadian clock associated 1 (CCA1) and late elongated hypocotyl (LHY) to restrict their expression to near dawn, but the mechanism has been unclear. Here we report that members of the plant Groucho/Tup1 corepressor family, topless/topless-related (TPL/TPR), interact with these three PRR proteins at the CCA1 and LHY promoters to repress transcription and alter circadian period. This activity is diminished in the presence of the inhibitor trichostatin A, indicating the requirement of histone deacetylase for full TPL activity. Additionally, a complex of PRR9, TPL, and histone deacetylase 6, can form in vivo, implicating this tripartite association as a central repressor of circadian gene expression. Our findings show that the TPL/TPR corepressor family are components of the central circadian oscillator mechanism and reinforces the role of this family as central to multiple signaling pathways in higher plants.
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