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Daniel Seaton

About Daniel Seaton:
No description specified

SEEK ID: https://fairdomhub.org/people/851

Location:  United Kingdom

Expertise: Not specified

Tools: Not specified

ORCID: https://orcid.org/0000-0002-5222-3893

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Regulation of flowering time in natural conditions

Research programme in the Takato Imaizumi lab, with multiple collaborators. Published in Song et al. Nature Plants 2018; Kinmonth-Schultz et al., in silico Plant 2019.

Programme: SynthSys

Public web page: https://faculty.washington.edu/takato/

Millar group

Andrew Millar's research group, University of Edinburgh

Programme: SynthSys

Public web page: http://www.amillar.org

TiMet

EU FP7 collaborative project TiMet, award number 245143. Funded 2010-2015.
"TiMet assembles world leaders in experimental and theoretical plant systems biology to advance understanding of the regulatory interactions between the circadian clock and plant metabolism, and their emergent effects on whole-plant growth and productivity."

Programme: SynthSys

Public web page: http://timing-metabolism.eu/

University of Edinburgh

Country:  United Kingdom

City: Edinburgh

Web page: http://www.ed.ac.uk/

Temperature effects on Arabidopsis floral induction at the leaf-specific level
Millar group, Regulation of flowering time in natural conditions, PlaSMo model repository

Project to test effects of temperature cycles on expression of Arabidopsis florigen gene FT, and whether these are mediated by temperature-dependent leaf development or temperature-specific FT expression, or both. Re-used and extended Arabidopsis Framework Model v1 to address this question. Led by Hannah Kinmonth-Schultz in Kim and Imaizumi labs, collaborating with Millar lab.

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Photoperiodic control of the Arabidopsis proteome reveals a translational coincidence mechanism
Millar group, TiMet

Click on Snapshot 2 to download data, models and analysis for Daniel Seaton et al.
biorXiv 2017 https://doi.org/10.1101/182071 and
Molecular Systems Biology, accepted Jan 2018, https://doi.org/10.15252/msb.20177962.
Note that the published paper cannot be fully linked into this record as the DOI above was not live when we made the Research Object from this Investigation on FAIRDOMHub.

Snapshots: Snapshot 1, Snapshot 2

DOI: 10.15490/fairdomhub.1.investigation.163.2

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Translational coincidence model
Millar group, TiMet

These Python scripts define and simulate the translational coincidence model. This model takes measured transcript dynamics (Blasing et al, 2005) in 12L:12D, measured synthesis rates of protein in light compared to dark (Pal et al, 2013), and outputs predicted changes in protein abundance between short (6h) and long (18h) photoperiods. These are compared to the photoperiod proteomics dataset we generated.

Contributor: Daniel Seaton

Biological problem addressed: Model Analysis Type

Snapshots: No snapshots

Estimation of rates of translation and turnover from proteomics datasets
Millar group, TiMet

Data and Python scripts to run the analysis of literature data that estimates rates of protein synthesis in the light and dark, and overall rates of protein turnover, in Cyanothece and Ostrecoccus tauri.

Contributor: Daniel Seaton

Biological problem addressed: Model Analysis Type

Snapshots: No snapshots

Aryal et al, 2011, metabolic labelling of Cyanothece protein synthesis
Millar group, TiMet

Quantitative proteomic analysis of Cyanothece ATCC51142 grown in 12L:12D light:dark cycles, using partial metabolic labeling and LC-MS analysis.

Contributor: Daniel Seaton

Assay type: Proteomics

Technology type: Mass Spectrometry

Snapshots: No snapshots

Martin et al, 2012, Ostreococcus N15 labelling proteomics data
Millar group, TiMet

Proteomics data for N15 incorporation into protein in Ostreococcus grown in 12L:12D light:dark cycles.

Contributor: Daniel Seaton

Assay type: Proteomics

Technology type: Mass Spectrometry

Snapshots: No snapshots

Blasing et al, 2005, diurnal microarray in 12L:12D
Millar group, TiMet
No description specified

Contributor: Daniel Seaton

Assay type: Gene Expression Profiling

Technology type: Microarray

Snapshots: No snapshots

Photoperiod proteomics
Millar group, TiMet

Plant material
The same plant material used for transcriptome analysis in (Flis et al., 2016) was the basis of our proteome study. Briefly, Arabidopsis thaliana Col-0 plants were grown on GS 90 soil mixed in a ratio 2:1 (v/v) with vermiculite. Plants were grown for 1 week in a 16 h light (250 μmol m−2 s−1, 20 °C)/8 h dark (6 °C) regime followed by an 8 h light (160 μmol m−2 s−1, 20 °C)/16 h dark (16 °C) regime for one week. Plants were then replanted with five seedlings per pot, transferred for
...

Contributor: Daniel Seaton

Assay type: Protein Quantification

Technology type: Mass Spectrometry

Snapshots: No snapshots

Stitt lab, TiMet photoperiod microarrays
Millar group, TiMet

Transcript profiling by microarray in 4, 6, 8, 12 and 18 h photoperiods, originally published in Flis et al, 2016, Photoperiod-dependent changes in the phase of core clock transcripts and global transcriptional outputs at dawn and dusk in Arabidopsis. doi: 10.1111/pce.12754.

Contributor: Daniel Seaton

Assay type: Gene Expression Profiling

Technology type: Microarray

Snapshots: No snapshots

9 hidden items
Calculated rates of protein synthesis in the light and dark in Ostreococcus tauri
Millar group
No description specified

Creators: Daniel Seaton, Andrew Millar

Contributor: Daniel Seaton

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Calculated rates of protein synthesis in the light and dark in Cyanothece ATCC51142
Millar group
No description specified

Creator: Daniel Seaton

Contributor: Daniel Seaton

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Calculated rates of protein degradation in Cyanothece ATCC51142
Millar group
No description specified

Creator: Daniel Seaton

Contributor: Daniel Seaton

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Calculated rates of protein degradation in Ostreococcus tauri
Millar group
No description specified

Creator: Daniel Seaton

Contributor: Daniel Seaton

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Aryal et al, 2011, metabolic labelling of Cyanothece protein synthesis
Millar group

Quantitative proteomic analysis of Cyanothece ATCC51142 grown in 12L:12D light:dark cycles, using partial metabolic labeling and LC-MS analysis.

Creators: Daniel Seaton, Andrew Millar

Contributor: Daniel Seaton

Download
Martin et al, 2012, Ostreococcus N15 labelling proteomics
Millar group

Proteomics data for N15 incorporation into protein in Ostreococcus grown in 12L:12D light:dark cycles.

Creators: Daniel Seaton, Andrew Millar

Contributor: Daniel Seaton

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Blasing et al, 2005, diurnal microarray dataset in 12L:12D
Millar group, TiMet
No description specified

Creator: Daniel Seaton

Contributor: Daniel Seaton

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Table EV3, Statistical analysis of protein changes across photoperiods
Millar group, TiMet

Results of the statistical analysis, identifying proteins that change in abundance significantly across photoperiods.

Creators: Daniel Seaton, Andrew Millar

Contributor: Daniel Seaton

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Table EV1 - Quantitative proteomics dataset
Millar group, TiMet

Mean and standard deviation of protein abundances in 6h, 8h, 12h, and 18h photoperiods.

Creators: Daniel Seaton, Andrew Millar

Contributor: Daniel Seaton

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Flis et al, 2016, Supplemental Table S4, Global expression profiles
Millar group, TiMet

Microarray data at end of day (ED) and end of night (EN) in 4, 6, 8, 12, and 18h photoperiods.

Creator: Daniel Seaton

Contributor: Daniel Seaton

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Framework Model v2
Millar group, TiMet

Framework Model for Arabidopsis vegetative growth, version 2 (FMv2), as described in Chew et al. bioRxiv 2017 (https://doi.org/10.1101/105437; please see linked Article file).

The FMv2 model record on FAIRDOMHub has the following versions, which represent the same FMv2 model:
Version 1 is an archive of the github repository of MATLAB code for the Framework Model v2, downloaded from https://github.com/danielseaton/frameworkmodel on 06/02/17. This version was not licensed for further use and was
...

Creators: Daniel Seaton, Yin Hoon Chew, Andrew Millar

Contributor: Daniel Seaton

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Estimation of translation and turnover - python scripts
Millar group

Python scripts to run the analysis estimating rates of protein synthesis in the light and dark, and overall rates of protein turnover, in Cyanothece and Ostrecoccus tauri.

Creators: Daniel Seaton, Andrew Millar

Contributor: Daniel Seaton

Download
Translational coincidence modelling - python scripts
Millar group
No description specified

Creator: Daniel Seaton

Contributor: Daniel Seaton

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2 hidden items
Proteome turnover in the green alga Ostreococcus tauri by time course 15N metabolic labeling mass spectrometry.
Millar group

Abstract (Expand)

Protein synthesis and degradation determine the cellular levels of proteins, and their control hence enables organisms to respond to environmental change. Experimentally, these are little known proteome … parameters; however, recently, SILAC-based mass spectrometry studies have begun to quantify turnover in the proteomes of cell lines, yeast, and animals. Here, we present a proteome-scale method to quantify turnover and calculate synthesis and degradation rate constants of individual proteins in autotrophic organisms such as algae and plants. The workflow is based on the automated analysis of partial stable isotope incorporation with (15)N. We applied it in a study of the unicellular pico-alga Ostreococcus tauri and observed high relative turnover in chloroplast-encoded ATPases (0.42-0.58% h(-1)), core photosystem II proteins (0.34-0.51% h(-1)), and RbcL (0.47% h(-1)), while nuclear-encoded RbcS2 is more stable (0.23% h(-1)). Mitochondrial targeted ATPases (0.14-0.16% h(-1)), photosystem antennae (0.09-0.14% h(-1)), and histones (0.07-0.1% h(-1)) were comparatively stable. The calculation of degradation and synthesis rate constants k(deg) and k(syn) confirms RbcL as the bulk contributor to overall protein turnover. This study performed over 144 h of incorporation reveals dynamics of protein complex subunits as well as isoforms targeted to different organelles.

Authors: S. F. Martin, V. S. Munagapati, E. Salvo-Chirnside, L. E. Kerr, T. Le Bihan

Date Published: No date defined

Journal: J Proteome Res

Dynamic proteomic profiling of a unicellular cyanobacterium Cyanothece ATCC51142 across light-dark diurnal cycles.
Millar group

Abstract (Expand)

BACKGROUND: Unicellular cyanobacteria of the genus Cyanothece are recognized for their ability to execute nitrogen (N2)-fixation in the dark and photosynthesis in the light. An understanding of these … mechanistic processes in an integrated systems context should provide insights into how Cyanothece might be optimized for specialized environments and/or industrial purposes. Systems-wide dynamic proteomic profiling with mass spectrometry (MS) analysis should reveal fundamental insights into the control and regulation of these functions. RESULTS: To expand upon the current knowledge of protein expression patterns in Cyanothece ATCC51142, we performed quantitative proteomic analysis using partial ("unsaturated") metabolic labeling and high mass accuracy LC-MS analysis. This dynamic proteomic profiling identified 721 actively synthesized proteins with significant temporal changes in expression throughout the light-dark cycles, of which 425 proteins matched with previously characterized cycling transcripts. The remaining 296 proteins contained a cluster of proteins uniquely involved in DNA replication and repair, protein degradation, tRNA synthesis and modification, transport and binding, and regulatory functions. Functional classification of labeled proteins suggested that proteins involved in respiration and glycogen metabolism showed increased expression in the dark cycle together with nitrogenase, suggesting that N2-fixation is mediated by higher respiration and glycogen metabolism. Results indicated that Cyanothece ATCC51142 might utilize alternative pathways for carbon (C) and nitrogen (N) acquisition, particularly, aspartic acid and glutamate as substrates of C and N, respectively. Utilization of phosphoketolase (PHK) pathway for the conversion of xylulose-5P to pyruvate and acetyl-P likely constitutes an alternative strategy to compensate higher ATP and NADPH demand. CONCLUSION: This study provides a deeper systems level insight into how Cyanothece ATCC51142 modulates cellular functions to accommodate photosynthesis and N2-fixation within the single cell.

Authors: U. K. Aryal, J. Stockel, R. K. Krovvidi, M. A. Gritsenko, M. E. Monroe, R. J. Moore, D. W. Koppenaal, R. D. Smith, H. B. Pakrasi, J. M. Jacobs

Date Published: No date defined

Journal: BMC Syst Biol

Sugars and circadian regulation make major contributions to the global regulation of diurnal gene expression in Arabidopsis.
Millar group

Abstract (Expand)

The diurnal cycle strongly influences many plant metabolic and physiological processes. Arabidopsis thaliana rosettes were harvested six times during 12-h-light/12-h-dark treatments to investigate … changes in gene expression using ATH1 arrays. Diagnostic gene sets were identified from published or in-house expression profiles of the response to light, sugar, nitrogen, and water deficit in seedlings and 4 h of darkness or illumination at ambient or compensation point [CO(2)]. Many sugar-responsive genes showed large diurnal expression changes, whose timing matched that of the diurnal changes of sugars. A set of circadian-regulated genes also showed large diurnal changes in expression. Comparison of published results from a free-running cycle with the diurnal changes in Columbia-0 (Col-0) and the starchless phosphoglucomutase (pgm) mutant indicated that sugars modify the expression of up to half of the clock-regulated genes. Principle component analysis identified genes that make large contributions to diurnal changes and confirmed that sugar and circadian regulation are the major inputs in Col-0 but that sugars dominate the response in pgm. Most of the changes in pgm are triggered by low sugar levels during the night rather than high levels in the light, highlighting the importance of responses to low sugar in diurnal gene regulation. We identified a set of candidate regulatory genes that show robust responses to alterations in sugar levels and change markedly during the diurnal cycle.

Authors: O. E. Blasing, Y. Gibon, M. Gunther, M. Hohne, R. Morcuende, D. Osuna, O. Thimm, B. Usadel, W. R. Scheible, M. Stitt

Date Published: No date defined

Journal: Plant Cell

Global transcript levels respond to small changes of the carbon status during progressive exhaustion of carbohydrates in Arabidopsis rosettes.
Millar group

Abstract (Expand)

The balance between the supply and utilization of carbon (C) changes continually. It has been proposed that plants respond in an acclimatory manner, modifying C utilization to minimize harmful periods … of C depletion. This hypothesis predicts that signaling events are initiated by small changes in C status. We analyzed the global transcriptional response to a gradual depletion of C during the night and an extension of the night, where C becomes severely limiting from 4 h onward. The response was interpreted using published datasets for sugar, light, and circadian responses. Hundreds of C-responsive genes respond during the night and others very early in the extended night. Pathway analysis reveals that biosynthesis and cellular growth genes are repressed during the night and genes involved in catabolism are induced during the first hours of the extended night. The C response is amplified by an antagonistic interaction with the clock. Light signaling is attenuated during the 24-h light/dark cycle. A model was developed that uses the response of 22K genes during a circadian cycle and their responses to C and light to predict global transcriptional responses during diurnal cycles of wild-type and starchless pgm mutant plants and an extended night in wild-type plants. By identifying sets of genes that respond at different speeds and times during C depletion, our extended dataset and model aid the analysis of candidates for C signaling. This is illustrated for AKIN10 and four bZIP transcription factors, and sets of genes involved in trehalose signaling, protein turnover, and starch breakdown.

Authors: B. Usadel, O. E. Blasing, Y. Gibon, K. Retzlaff, M. Hohne, M. Gunther, M. Stitt

Date Published: No date defined

Journal: Plant Physiol

Photoperiod-dependent changes in the phase of core clock transcripts and global transcriptional outputs at dawn and dusk in Arabidopsis.
Millar group, TiMet

Abstract (Expand)

Plants use the circadian clock to sense photoperiod length. Seasonal responses like flowering are triggered at a critical photoperiod when a light-sensitive clock output coincides with light or darkness. … However, many metabolic processes, like starch turnover, and growth respond progressively to photoperiod duration. We first tested the photoperiod response of 10 core clock genes and two output genes. qRT-PCR analyses of transcript abundance under 6, 8, 12 and 18 h photoperiods revealed 1-4 h earlier peak times under short photoperiods and detailed changes like rising PRR7 expression before dawn. Clock models recapitulated most of these changes. We explored the consequences for global gene expression by performing transcript profiling in 4, 6, 8, 12 and 18 h photoperiods. There were major changes in transcript abundance at dawn, which were as large as those between dawn and dusk in a given photoperiod. Contributing factors included altered timing of the clock relative to dawn, light signalling and changes in carbon availability at night as a result of clock-dependent regulation of starch degradation. Their interaction facilitates coordinated transcriptional regulation of key processes like starch turnover, anthocyanin, flavonoid and glucosinolate biosynthesis and protein synthesis and underpins the response of metabolism and growth to photoperiod.

Authors: A. Flis, R. Sulpice, D. D. Seaton, A. A. Ivakov, M. Liput, C. Abel, A. J. Millar, M. Stitt

Date Published: No date defined

Journal: Plant Cell Environ

Circadian protein regulation in the green lineage I. A phospho-dawn anticipates light onset before proteins peak in daytime.
Millar group

Abstract (Expand)

BioRxiv preprint, 4 April 2018. Abstract: Daily light-dark cycles (LD) drive dynamic regulation of plant and algal transcriptomes via photoreceptor pathways and 24-hour, circadian rhythms. Diel regulation … of protein levels and modifications has been less studied. Ostreococcus tauri, the smallest free-living eukaryote, provides a minimal model proteome for the green lineage. Here, we compare transcriptome data under LD to the algal proteome and phosphoproteome, assayed using shotgun mass-spectrometry. Under 10% of 855 quantified proteins were rhythmic but two-thirds of 860 phosphoproteins showed rhythmic modification(s). Most rhythmic proteins peaked in the daytime. Model simulations showed that light-stimulated protein synthesis largely accounts for this distribution of protein peaks. Prompted by apparently dark-stable proteins, we sampled during prolonged dark adaptation, where stable RNAs and very limited change to the proteome suggested a quiescent, cellular “dark state”. In LD, acid-directed and proline-directed protein phosphorylation sites were regulated in antiphase. Strikingly, 39% of rhythmic phospho-sites reached peak levels just before dawn. This anticipatory phosphorylation is distinct from light-responsive translation but consistent with plant phosphoprotein profiles, suggesting that a clock-regulated phospho-dawn prepares green cells for daytime functions.

Authors: Zeenat B. Noordally, Matthew M. Hindle, Sarah F. Martin, Daniel Seaton, Ian Simpson, Thierry Le Bihan, Andrew Millar

Date Published: No date defined

Journal: Not specified

Mechanistic model of temperature influence on flowering through whole-plant accumulation of FT
Regulation of flowering time in natural conditions

Abstract

BioRxiv preprint:

Authors: Hannah A Kinmonth-Schultz, Melissa J MacEwen, Daniel Seaton, Andrew Millar, Takato Imaizumi, Soo-Hyung Kim

Date Published: No date defined

Journal: Not specified

Photoperiodic control of the Arabidopsis proteome reveals a translational coincidence mechanism
Millar group

Abstract (Expand)

bioRxiv preprint 2017 Plants respond to seasonal cues such as the photoperiod, to adapt to current conditions and to prepare for environmental changes in the season to come. To assess photoperiodic … responses at the protein level, we quantified the proteome of the model plant Arabidopsis thaliana by mass spectrometry across four photoperiods. This revealed coordinated changes of abundance in proteins of photosynthesis, primary and secondary metabolism, including pigment biosynthesis, consistent with higher metabolic activity in long photoperiods. Higher translation rates in the day time than the night likely contribute to these changes via rhythmic changes in RNA abundance. Photoperiodic control of protein levels might be greatest only if high translation rates coincide with high transcript levels in some photoperiods. We term this proposed mechanism ‘translational coincidence’, mathematically model its components, and demonstrate its effect on the Arabidopsis proteome. Datasets from a green alga and a cyanobacterium suggest that translational coincidence contributes to seasonal control of the proteome in many phototrophic organisms. This may explain why many transcripts but not their cognate proteins exhibit diurnal rhythms.

Authors: Daniel Seaton, Alexander Graf, Katja Baerenfaller, Mark Stitt, Andrew Millar, Wilhelm Gruissem

Date Published: No date defined

Journal: Not specified

Linking circadian time to growth rate quantitatively via carbon metabolism
Millar group

Abstract (Expand)

Predicting a multicellular organism's phenotype quantitatively from its genotype is challenging, as genetic effects must propagate up time and length scales. Circadian clocks are intracellular … regulators that control temporal gene expression patterns and hence metabolism, physiology and behaviour, from sleep/wake cycles in mammals to flowering in plants1-3. Clock genes are rarely essential but appropriate alleles can confer a competitive advantage4,5 and have been repeatedly selected during crop domestication3,6. Here we quantitatively explain and predict canonical phenotypes of circadian timing in a multicellular, model organism. We used metabolic and physiological data to combine and extend mathematical models of rhythmic gene expression, photoperiod-dependent flowering, elongation growth and starch metabolism within a Framework Model for growth of Arabidopsis thaliana7-9. The model predicted the effect of altered circadian timing upon each particular phenotype in clock-mutant plants. Altered night-time metabolism of stored starch accounted for most but not all of the decrease in whole-plant growth rate. Altered mobilisation of a secondary store of organic acids quantitatively explained the remaining defect. Our results link genotype through specific processes to higher-level phenotypes, formalising our understanding of a subtle, pleiotropic syndrome at the whole-organism level, and validating the systems approach to understand complex traits starting from intracellular circuits.

Authors: Yin Hoon Chew, Daniel Seaton, Virginie Mengin, Anna Flis, Sam T. Mugford, Alison M. Smith, Mark Stitt, Andrew Millar

Date Published: No date defined

Journal: Not specified

Linked circadian outputs control elongation growth and flowering in response to photoperiod and temperature
Millar group

Abstract (Expand)

Clock-regulated pathways coordinate the response of many developmental processes to changes in photoperiod and temperature. We model two of the best-understood clock output pathways in Arabidopsis, … which control key regulators of flowering and elongation growth. In flowering, the model predicted regulatory links from the clock to cycling DOF factor 1 (CDF1) and flavin-binding, KELCH repeat, F-box 1 (FKF1) transcription. Physical interaction data support these links, which create threefold feed-forward motifs from two clock components to the floral regulator FT. In hypocotyl growth, the model described clock-regulated transcription of phytochrome-interacting factor 4 and 5 (PIF4, PIF5), interacting with post-translational regulation of PIF proteins by phytochrome B (phyB) and other light-activated pathways. The model predicted bimodal and end-of-day PIF activity profiles that are observed across hundreds of PIF-regulated target genes. In the response to temperature, warmth-enhanced PIF4 activity explained the observed hypocotyl growth dynamics but additional, temperature-dependent regulators were implicated in the flowering response. Integrating these two pathways with the clock model highlights the molecular mechanisms that coordinate plant development across changing conditions.

Authors: Daniel Seaton, R. W. Smith, Y. H. Song, D. R. MacGregor, K. Stewart, G. Steel, J. Foreman, S. Penfield, T. Imaizumi, Andrew Millar, K. J. Halliday

Date Published: 21st Jan 2015

Journal: Mol Syst Biol

Regulatory principles and experimental approaches to the circadian control of starch turnover
Millar group

Abstract (Expand)

In many plants, starch is synthesized during the day and degraded during the night to avoid carbohydrate starvation in darkness. The circadian clock participates in a dynamic adjustment of starch … turnover to changing environmental condition through unknown mechanisms. We used mathematical modelling to explore the possible scenarios for the control of starch turnover by the molecular components of the plant circadian clock. Several classes of plausible models were capable of describing the starch dynamics observed in a range of clock mutant plants and light conditions, including discriminating circadian protocols. Three example models of these classes are studied in detail, differing in several important ways. First, the clock components directly responsible for regulating starch degradation are different in each model. Second, the intermediate species in the pathway may play either an activating or inhibiting role on starch degradation. Third, the system may include a light-dependent interaction between the clock and downstream processes. Finally, the clock may be involved in the regulation of starch synthesis. We discuss the differences among the models' predictions for diel starch profiles and the properties of the circadian regulators. These suggest additional experiments to elucidate the pathway structure, avoid confounding results and identify the molecular components involved.

Authors: Daniel Seaton, O. Ebenhoh, Andrew Millar, A. Pokhilko

Date Published: 18th Dec 2013

Journal: J R Soc Interface

The circadian clock regulates the photoperiodic response of hypocotyl elongation through a coincidence mechanism in Arabidopsis thaliana
Millar group

Abstract (Expand)

The plant circadian clock generates rhythms with a period close to 24 h, and it controls a wide range of physiological and developmental oscillations in habitats under natural light/dark cycles. Among … clock-controlled developmental events, the best characterized is the photoperiodic control of flowering time in Arabidopsis thaliana. Recently, it was also reported that the clock regulates a daily and rhythmic elongation of hypocotyls. Here, we report that the promotion of hypocotyl elongation is in fact dependent on changes in photoperiods in such a way that an accelerated hypocotyl elongation occurs especially under short-day conditions. In this regard, we provide genetic evidence to show that the circadian clock regulates the photoperiodic (or seasonal) elongation of hypocotyls by modulating the expression profiles of the PIF4 and PIF5 genes encoding phytochrome-interacting bHLH (basic helix-loop-helix) factors, in such a manner that certain short-day conditions are necessary to enhance the expression of these genes during the night-time. In other words, long-day conditions are insufficient to open the clock-gate for triggering the expression of PIF4 and PIF5 during the night-time. Based on these and other results, the photoperiodic control of hypocotyl elongation is best explained by the accumulation of PIF4 and PIF5 during the night-time of short days, due to coincidence between the internal (circadian rhythm) and external (photoperiod) time cues. This mechanism is a mirror image of the photoperiod-dependent promotion of flowering in that plants should experience long-day conditions to initiate flowering promptly. Both of these clock-mediated coincidence mechanisms may coordinately confer ecological fitness to plants growing in natural habitats with varied photoperiods.

Authors: Y. Niwa, T. Yamashino, T. Mizuno

Date Published: 24th Feb 2009

Journal: Plant Cell Physiol

Arabidopsis clock-associated pseudo-response regulators PRR9, PRR7 and PRR5 coordinately and positively regulate flowering time through the canonical CONSTANS-dependent photoperiodic pathway
Millar group

Abstract (Expand)

Photoperiodism allows organisms to measure daylength, or external photoperiod, and to anticipate coming seasons. Daylength measurement requires the integration of light signal and temporal information … by the circadian clock. In the long-day plant Arabidopsis thaliana, CONSTANS (CO) plays a crucial role in integrating the circadian rhythm and environmental light signals into the photoperiodic flowering pathway. Nevertheless, the molecular mechanism by which the circadian clock modulates the cyclic expression profile of CO is poorly understood. Here, we first showed that the clock-associated genes PSEUDO-RESPONSE REGULATOR (PRR) PRR9, PRR7 and PRR5 are involved in activation of CO expression during the daytime. Then, extensive genetic studies using CIRCADIAN CLOCK-ASSOCIATED1 (CCA1)/LATE ELONGATED HYPOCOTYL (LHY) double mutants (cca1/lhy) and prr7/prr5 were conducted. The results suggested that PRR genes act coordinately in a manner parallel with and antagonistic to CCA/LHY, upstream of the canonical CO-FLOWERING LOCUS T (FT) photoperiodic flowering pathway. Finally, we provided evidence to propose a model, in which CCA1/LHY repress CO through GIGANTEA (GI), while PRR9, PRR7 and PRR5 activate CO predominantly by repressing CYCLING DOF FACTOR1 (CDF1) encoding a DNA-binding transcriptional repressor.

Authors: N. Nakamichi, M. Kita, K. Niinuma, S. Ito, T. Yamashino, T. Mizoguchi, T. Mizuno

Date Published: 17th May 2007

Journal: Plant Cell Physiol

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