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  • 1. Anderson, James V.
    Ramos-Sánchez, José M.
    Conde, Daniel
    Ibáñez, Christian
    Takata, Naoki
    Allona, Isabel
    Eriksson, Maria E.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Role of the Circadian Clock in Cold Acclimation and Winter Dormancy in Perennial Plants2015Collection (editor) (Refereed)
    Abstract [en]

    Seasonal variation is a strong cue directing the growth and development of plants. It is particularly important for perennials growing in temperate and boreal regions where woody plants must become dormant to survive freezing winter temperatures. Shortening of the photoperiod induces growth cessation, bud set and a first degree of cold acclimation in most woody plants. The subsequent drop in temperature then produces a greater tolerance to cold and, in deciduous trees, leaf senescence and fall. Trees must time their periods of dormancy accurately with their environment. Circadian clocks underlie this ability, allowing organisms to predict regular, daily changes in their environment as well as longer term seasonal changes. This chapter provides an update on the plant clock in a model annual, thale cress (Arabidopsis thaliana), and further summarizes recent advances about the clock in perennial plants and its involvement in their annual growth cycles, which allows trees to withstand cold and freezing temperatures. Moreover, we outline our views on areas where future work on the circadian clock is necessary to gain insight into the life of a tree.

  • 2.
    Ashelford, Kevin
    et al.
    School of Biological Sciences, University of Liverpool, Liverpool, UK.
    Eriksson, Maria E
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Allen, Christopher M
    Applied Biosystems, part of Life Technologies, Warrington, UK.
    D’Amore, Linda
    School of Biological Sciences, University of Liverpool, Liverpool, UK.
    Johansson, Mikael
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gould, Peter
    School of Biological Sciences, University of Liverpool, Liverpool, UK.
    Kay, Susanne
    School of Biological Sciences, University of Liverpool, Liverpool, UK.
    Millar, Andrew J.
    Institute of Molecular Plant Sciences, School of Biological Sciences, University of Edinburgh, Edinburgh, UK.
    Hall, Neil
    School of Biological Sciences, University of Liverpool, Liverpool, UK.
    Hall, Anthony
    School of Biological Sciences, University of Liverpool, Liverpool, UK.
    Full genome re-sequencing reveals a novel circadian clock mutationin Arabidopsis2011In: Genome Biology, ISSN 1465-6906, E-ISSN 1474-760X, Vol. 12, p. R28-Article in journal (Refereed)
    Abstract [en]

    Background: Map based cloning in Arabidopsis thaliana can be a difficult and time-consuming process,specifically if the phenotype is subtle and scoring labour intensive. An alternative to map basedcloning would be to directly sequence the whole genome of a mutant to uncover the mutationresponsible for the phenotype.

    Results: Here, we have re-sequenced the 120 Mb genome of a novel Arabidopsis clock mutant earlybird (ebi-1), using massively parallel sequencing by ligation. This process was further complicated by the fact that ebi-1 is in Wassilewskija (Ws-2), not the reference accession ofArabidopsis. The approach reveals evidence of DNA strand bias in the ethyl methanesulfonate(EMS) mutation process. We have demonstrated the utility of sequencing a backcrossed line andusing gene expression data to limit the number of SNP considered. Using new SNP informationwe have excluded a previously identified clock gene, PRR7. Finally, we have identified a SNPin the gene AtNFXL-2 as the likely cause of the ebi-1 phenotype and validated this bycharacterising a further allele.

    Conclusion: In Arabidopsis, as in other organisms, the (EMS) mutation load can be high. Here wedescribe how sequencing a backcrossed line, using functional genomics and analysing new SNPinformation can be used to reduce the number EMS mutations for consideration. Moreover, theapproach we describe here does not require out-crossing and scoring F2 mapping populations, anapproach which can be compromised by background effects. The strategy has broad utility andwill be an extremely useful tool to identify causative SNP in other organisms.

  • 3. Cooke, Janice E. K.
    et al.
    Eriksson, Maria E.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Junttila, Olavi
    The dynamic nature of bud dormancy in trees: environmental control and molecular mechanisms2012In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 35, no 10, p. 1707-1728Article in journal (Refereed)
    Abstract [en]

    In tree species native to temperate and boreal regions, the activity-dormancy cycle is an important adaptive trait both for survival and growth. We discuss recent research on mechanisms controlling the overlapping developmental processes that define the activity-dormancy cycle, including cessation of apical growth, bud development, induction, maintenance and release of dormancy, and bud burst. The cycle involves an extensive reconfiguration of metabolism. Environmental control of the activity-dormancy cycle is based on perception of photoperiodic and temperature signals, reflecting adaptation to prevailing climatic conditions. Several molecular actors for control of growth cessation have been identified, with the CO/FT regulatory network and circadian clock having important coordinating roles in control of growth and dormancy. Other candidate regulators of bud set, dormancy and bud burst have been identified, such as dormancy-associated MADS-box factors, but their exact roles remain to be discovered. Epigenetic mechanisms also appear to factor in control of the activity-dormancy cycle. Despite evidence for gibberellins as negative regulators in growth cessation, and ABA and ethylene in bud formation, understanding of the roles that plant growth regulators play in controlling the activity-dormancy cycle is still very fragmentary. Finally, some of the challenges for further research in bud dormancy are discussed.

  • 4. Ding, Jihua
    et al.
    Böhlenius, Henrik
    Rühl, Mark Georg
    Chen, Peng
    Sane, Shashank
    Zambrano, Jose A.
    Zheng, Bo
    Nilsson, Ove
    Eriksson, Maria E.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    GIGANTEA-like genes control seasonal growth cessation in Populus2018In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 218, no 4, p. 1491-1503Article in journal (Refereed)
    Abstract [en]

    Survival of trees growing in temperate zones requires cycling between active growth and dormancy. This involves growth cessation in the autumn triggered by a photoperiod shorter than the critical day length. Variations in GIGANTEA (GI)-like genes have been associated with phenology in a range of different tree species, but characterization of the functions of these genes in the process is still lacking. We describe the identification of the Populus orthologs of GI and their critical role in short-day-induced growth cessation. Using ectopic expression and silencing, gene expression analysis, protein interaction and chromatin immunoprecipitation experiments, we show that PttGIs are likely to act in a complex with PttFKF1s (FLAVIN-BINDING, KELCH REPEAT, F-BOX 1) and PttCDFs (CYCLING DOF FACTOR) to control the expression of PttFT2, the key gene regulating short-day-induced growth cessation in Populus. In contrast to Arabidopsis, in which the GI-CONSTANS (CO)-FLOWERING LOCUS T (FT) regulon is a crucial day-length sensor for flowering time, our study suggests that, in Populus, PttCO-independent regulation of PttFT2 by PttGI is more important in the photoperiodic control of growth cessation and bud set.

  • 5. Edwards, Kieron D.
    et al.
    Takata, Naoki
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Johansson, Mikael
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). RNA Biology and Molecular Physiology, Bielefeld University, Bielefeld, Germany.
    Jurca, Manuela
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Novak, Ondrej
    Henykova, Eva
    Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Liverani, Silvia
    Kozarewa, Iwanka
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Strnad, Miroslav
    Millar, Andrew J.
    Ljung, Karin
    Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Eriksson, Maria E.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Circadian clock components control daily growth activities by modulating cytokinin levels and cell division-associated gene expression in Populus trees2018In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 41, no 6, p. 1468-1482Article in journal (Refereed)
    Abstract [en]

    Trees are carbon dioxide sinks and major producers of terrestrial biomass with distinct seasonal growth patterns. Circadian clocks enable the coordination of physiological and biochemical temporal activities, optimally regulating multiple traits including growth. To dissect the clock's role in growth, we analysed Populus tremula x P. tremuloides trees with impaired clock function due to down-regulation of central clock components. late elongated hypocotyl (lhy-10) trees, in which expression of LHY1 and LHY2 is reduced by RNAi, have a short free-running period and show disrupted temporal regulation of gene expression and reduced growth, producing 30-40% less biomass than wild-type trees. Genes important in growth regulation were expressed with an earlier phase in lhy-10, and CYCLIN D3 expression was misaligned and arrhythmic. Levels of cytokinins were lower in lhy-10 trees, which also showed a change in the time of peak expression of genes associated with cell division and growth. However, auxin levels were not altered in lhy-10 trees, and the size of the lignification zone in the stem showed a relative increase. The reduced growth rate and anatomical features of lhy-10 trees were mainly caused by misregulation of cell division, which may have resulted from impaired clock function.

  • 6.
    Eriksson, Maria E.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Hoffman, Daniel
    Kaduk, Mateusz
    Mauriat, Melanie
    Moritz, Thomas
    Transgenic hybrid aspen trees with increased gibberellin (GA) concentrations suggest that GA acts in parallel with FLOWERING LOCUS T2 to control shoot elongation2015In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 205, no 3, p. 1288-1295Article in journal (Refereed)
    Abstract [en]

    Bioactive gibberellins (GAs) have been implicated in short day (SD)-induced growth cessation in Populus, because exogenous applications of bioactive GAs to hybrid aspens (Populus tremulaxtremuloides) under SD conditions delay growth cessation. However, this effect diminishes with time, suggesting that plants may cease growth following exposure to SDs due to a reduction in sensitivity to GAs.

    In order to validate and further explore the role of GAs in growth cessation, we perturbed GA biosynthesis or signalling in hybrid aspen plants by overexpressing AtGA20ox1, AtGA2ox2 and PttGID1.3 (encoding GA biosynthesis enzymes and a GA receptor).

    We found trees with elevated concentrations of bioactive GA, due to overexpression of AtGA20ox1, continued to grow in SD conditions and were insensitive to the level of FLOWERING LOCUS T2 (FT2) expression. As transgenic plants overexpressing the PttGID1.3 GA receptor responded in a wild-type (WT) manner to SD conditions, this insensitivity did not result from limited receptor availability.

    As high concentrations of bioactive GA during SD conditions were sufficient to sustain shoot elongation growth in hybrid aspen trees, independent of FT2 expression levels, we conclude elongation growth in trees is regulated by both GA- and long day-responsive pathways, similar to the regulation of flowering in Arabidopsis thaliana.

  • 7.
    Eriksson, Maria E.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Webb, Alex A. R.
    Plant cell responses to cold are all about timing2011In: Current opinion in plant biology, ISSN 1369-5266, E-ISSN 1879-0356, Vol. 14, no 6, p. 731-737Article in journal (Refereed)
    Abstract [en]

    Changes in temperature present the cells of plants with particular challenges. Fortunately, many changes in temperature can be anticipated due to the rhythms of day/night and the seasons. To anticipate changes in the environment most organisms have a circadian clock to optimize daily and seasonal timing of gene expression, metabolism, physiology and cell biology. Circadian clocks comprised positive and negative feedback loops which ensure an internal period of approximately 24 hours. We describe the role of the circadian clock in modulating cellular cold signalling networks to prepare the cell for the onset of winter.

  • 8. Hoffman, Daniel E.
    et al.
    Jonsson, Pär
    Umeå University, Faculty of Science and Technology, Department of Chemistry. SweTree Technologies AB, Umeå, Sweden.
    Bylesjö, Max
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Almac Diagnostics Ltd, Craigavon, UK.
    Trygg, Johan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Antti, Henrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Eriksson, Maria E.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Moritz, Thomas
    Changes in diurnal patterns within the Populus transcriptome and metabolome in response to photoperiod variation2010In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 33, no 8, p. 1298-1313Article in journal (Refereed)
    Abstract [en]

    Changes in seasonal photoperiod provides an important environmental signal that affects the timing of winter dormancy in perennial, deciduous, temperate tree species, such as hybrid aspen (Populus tremula x Populus tremuloides). In this species, growth cessation, cold acclimation and dormancy are induced in the autumn by the detection of day-length shortening that occurs at a given critical day length. Important components in the detection of such day-length changes are photoreceptors and the circadian clock, and many plant responses at both the gene regulation and metabolite levels are expected to be diurnal. To directly examine this expectation and study components in these events, here we report transcriptomic and metabolomic responses to a change in photoperiod from long to short days in hybrid aspen. We found about 16% of genes represented on the arrays to be diurnally regulated, as assessed by our pre-defined criteria. Furthermore, several of these genes were involved in circadian-associated processes, including photosynthesis and primary and secondary metabolism. Metabolites affected by the change in photoperiod were mostly involved in carbon metabolism. Taken together, we have thus established a molecular catalog of events that precede a response to winter.

  • 9.
    Ibáñez, Cristian
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kozarewa, Iwanka
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Johansson, Mikael
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Ögren, Erling
    Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural ences, Umeå, Sweden.
    Rohde, Antje
    Department of Plant Growth and Development, Institute of Agricultural and Fisheries Research, 9090 Melle, Belgium.
    Eriksson, Maria E
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Circadian clock components regulate entry and affect exit of seasonal dormancy as well as winter hardiness in Populus trees2010In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 153, no 4, p. 1823-1833Article in journal (Refereed)
    Abstract [en]

    This study addresses the role of the circadian clock in the seasonal growth cycle of trees: growth cessation, bud set, freezing tolerance, and bud burst. Populus tremula x Populus tremuloides (Ptt) LATE ELONGATED HYPOCOTYL1 (PttLHY1), PttLHY2, and TIMING OF CAB EXPRESSION1 constitute regulatory clock components because down-regulation by RNA interference of these genes leads to altered phase and period of clock-controlled gene expression as compared to the wild type. Also, both RNA interference lines show about 1-h-shorter critical daylength for growth cessation as compared to the wild type, extending their period of growth. During winter dormancy, when the diurnal variation in clock gene expression stops altogether, down-regulation of PttLHY1 and PttLHY2 expression compromises freezing tolerance and the expression of C-REPEAT BINDING FACTOR1, suggesting a role of these genes in cold hardiness. Moreover, down-regulation of PttLHY1 and PttLHY2 causes a delay in bud burst. This evidence shows that in addition to a role in daylength-controlled processes, PttLHY plays a role in the temperature-dependent processes of dormancy in Populus such as cold hardiness and bud burst.

  • 10. Johansson, Mikael
    et al.
    Ibáñez, Cristian
    Takata, Naoki
    Eriksson, Maria E
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    The perennial clock is an essential timer for seasonal growth events and cold hardiness2014In: Plant Circadian Networks: Methods in Molecular Biology / [ed] Staiger D, New York: Springer, 2014, Vol. 1158, p. 297-311Chapter in book (Refereed)
    Abstract [en]

    Over the last several decades, changes in global temperatures have led to changes in local environments affecting the growth conditions for many species. This is a trend that makes it even more important to understand how plants respond to local variations and seasonal changes in climate. To detect daily and seasonal changes as well as acute stress factors such as cold and drought, plants rely on a circadian clock. This chapter introduces the current knowledge and literature about the setup and function of the circadian clock in various tree and perennial species, with a focus on the Populus genus.

  • 11.
    Johansson, Mikael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    McWatters, Harriet G
    Bako, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Takata, Naoki
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Gyula, Péter
    Hall, Anthony
    Somers, David E
    Millar, Andrew J
    Eriksson, Maria E
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Partners in time: early bird associates with zeitlupe and regulates the speed of the arabidopsis clock2011In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 155, no 4, p. 2108-2122Article in journal (Refereed)
    Abstract [en]

    The circadian clock of the model plant Arabidopsis (Arabidopsis thaliana) is made up of a complex series of interacting feedback loops whereby proteins regulate their own expression across day and night. early bird (ebi) is a circadian mutation that causes the clock to speed up: ebi plants have short circadian periods, early phase of clock gene expression, and are early flowering. We show that EBI associates with ZEITLUPE (ZTL), known to act in the plant clock as a posttranslational mediator of protein degradation. However, EBI is not degraded by its interaction with ZTL. Instead, ZTL counteracts the effect of EBI during the day and increases it at night, modulating the expression of key circadian components. The partnership of EBI with ZTL reveals a novel mechanism involved in controlling the complex transcription-translation feedback loops of the clock. This work highlights the importance of cross talk between the ubiquitination pathway and transcriptional control for regulation of the plant clock.

  • 12.
    Johansson, Mikael
    et al.
    Bielefeld, Germany .
    Takata, Naoki
    Hitachi, Japan .
    Ibáñez, Cristian
    La Serena, Chile.
    Eriksson, Maria E
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK .
    Monitoring seasonal bud set, bud burst, and cold hardiness in Populus2014In: Plant Circadian Networks: Methods and Protocols / [ed] Dorothee Steiger, New York: Springer Science+Business Media B.V., 2014, Vol. 1158, p. 313-324Chapter in book (Refereed)
    Abstract [en]

    Using a perennial model plant allows the study of reoccurring seasonal events in a way that is not possible using a fast-growing annual such as Arabidopsis thaliana (Arabidopsis). In this study, we present a hybrid aspen (Populus tremula × P. tremuloides) as our perennial model plant. These plants can be grown in growth chambers to shorten growth periods and manipulate day length and temperature in ways that would be impossible under natural conditions. In addition, the use of growth chambers allows easy monitoring of height and diameter expansion, accelerating the collection of data from new strategies that allow evaluation of promoters or inhibitors of growth. Here, we describe how to study and quantify responses to seasonal changes (mainly using P. tremula × P. tremuloides) by measuring growth rate and key events under different photoperiodic cycles.

  • 13. Kevei, Eva
    et al.
    Gyula, Péter
    Hall, Anthony
    Kozma-Bognár, László
    Kim, Woe-Yeon
    Eriksson, Maria
    Umeå University, Faculty of Science and Technology, Plant Physiology. Umeå Plant Science Centre.
    Tóth, Réka
    Hanano, Shigeru
    Fehér, Balázs
    Southern, Megan M
    Bastow, Ruth M
    Viczián, András
    Hibberd, Victoria
    Davis, Seth J
    Somers, David E
    Nagy, Ferenc
    Millar, Andrew J
    Forward genetic analysis of the circadian clock separates the multiple functions of ZEITLUPE.2006In: Plant Physiology, ISSN 0032-0889, Vol. 140, no 3, p. 933-45Article in journal (Refereed)
    Abstract [en]

    The circadian system of Arabidopsis (Arabidopsis thaliana) includes feedback loops of gene regulation that generate 24-h oscillations. Components of these loops remain to be identified; none of the known components is completely understood, including ZEITLUPE (ZTL), a gene implicated in regulated protein degradation. ztl mutations affect both circadian and developmental responses to red light, possibly through ZTL interaction with PHYTOCHROME B (PHYB). We conducted a large-scale genetic screen that identified additional clock-affecting loci. Other mutants recovered include 11 new ztl alleles encompassing mutations in each of the ZTL protein domains. Each mutation lengthened the circadian period, even in dark-grown seedlings entrained to temperature cycles. A mutation of the LIGHT, OXYGEN, VOLTAGE (LOV)/Period-ARNT-Sim (PAS) domain was unique in retaining wild-type responses to red light both for the circadian period and for control of hypocotyl elongation. This uncoupling of ztl phenotypes indicates that interactions of ZTL protein with multiple factors must be disrupted to generate the full ztl mutant phenotype. Protein interaction assays showed that the ztl mutant phenotypes were not fully explained by impaired interactions with previously described partner proteins Arabidopsis S-phase kinase-related protein 1, TIMING OF CAB EXPRESSION 1, and PHYB. Interaction with PHYB was unaffected by mutation of any ZTL domain. Mutation of the kelch repeat domain affected protein binding at both the LOV/PAS and the F-box domains, indicating that interaction among ZTL domains leads to the strong phenotypes of kelch mutations. Forward genetics continues to provide insight regarding both known and newly discovered components of the circadian system, although current approaches have saturated mutations at some loci.

  • 14.
    Kozarewa, Iwanka
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Ibáñez, Cristian
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Johansson, Mikael
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Ögren, Erling
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Mozley, David
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Nylander, Eva
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Chono, Makiko
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Moritz, Thomas
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Eriksson, Maria E
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Alteration of PHYA expression change circadian rhythms and timing of bud set in Populus2010In: Plant Molecular Biology, ISSN 0167-4412, E-ISSN 1573-5028, Vol. 73, no 1-2, p. 143-56Article in journal (Refereed)
    Abstract [en]

    In many temperate woody species, dormancy is induced by short photoperiods. Earlier studies have shown that the photoreceptor phytochrome A (phyA) promotes growth. Specifically, Populus plants that over-express the oat PHYA gene (oatPHYAox) show daylength-independent growth and do not become dormant. However, we show that oatPHYAox plants could be induced to set bud and become cold hardy by exposure to a shorter, non-24 h diurnal cycle that significantly alters the relative position between endogenous rhythms and perceived light/dark cycles. Furthermore, we describe studies in which the expression of endogenous Populus tremula x P. tremuloides PHYTOCHROME A (PttPHYA) was reduced in Populus trees by antisense inhibition. The antisense plants showed altered photoperiodic requirements, resulting in earlier growth cessation and bud formation in response to daylength shortening, an effect that was explained by an altered innate period that leads to phase changes of clock-associated genes such as PttCO2. Moreover, gene expression studies following far-red light pulses show a phyA-mediated repression of PttLHY1 and an induction of PttFKF1 and PttFT. We conclude that the level of PttPHYA expression strongly influences seasonally regulated growth in Populus and is central to co-ordination between internal clock-regulated rhythms and external light/dark cycles through its dual effect on the pace of clock rhythms and in light signaling.

  • 15. McWatters, Harriet G
    Plant Circadian Rhythms2016In: Encyclopedia of Life Sciences: Biological Sciences, Chichester: John Wiley & Sons, 2016, p. 1-10Chapter in book (Refereed)
    Abstract [en]

    Circadian clocks are found in most eukaryotic organisms. By allowing anticipation of daily and seasonal changes, they enable coordination of metabolism and lifecycle with the natural rhythms of the environment. Plant circadian rhythms are generated by a series of interlocking feedback loops of RNA (ribonucleic acid) and protein expression that respond to environmental cycles of light and temperature. They control essential processes in the plant's development, such as the transition to flowering or growth cessation, and thus influence yield, plant growth and biomass production. Many components of the clock are conserved across a wide variety of plant species and thus research in Arabidopsis translates into an understanding of the clock in agricultural crops or long‐living deciduous tree species such as hybrid aspen.

    Key Concepts

    • Circadian clocks are found in both eukaryotes and bacteria.
    • Circadian clocks have a free‐running periodicity of about 24 h but are normally entrained to environmental cycles of light and temperature.
    • Temperature compensation is a key feature of the circadian clock and thus the free‐running period length varies relatively little across the range of ambient temperature.
    • The clock underlies many aspects of plant metabolism and physiology because it can detect and respond to both short‐term (the day:night cycle) and long‐term (the pattern of daylength variation across a year) changes in light and temperature.
    • The circadian clock of plants is made up of a series of interconnected transcription‐translation feedback loops (TTFLs) governing cycles of mRNA and protein expression.
    • Every plant cell contains its own clock. Clocks in different cells may be entrained independently of one another, although there appears to be a hierarchy of clocks within a plant dominated by the apex.
    • Plants with malfunctioning clocks suffer reductions in growth.
    • Many of the key components of the plant clock first described in the model species Arabidopsis thaliana are conserved across a wide range of species including trees such as hybrid aspen.
  • 16. McWatters, Harriet G
    et al.
    Eriksson, Maria E
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Plant Circadian Rhythms2007In: eLS, Chichester: John Wiley & Sons, 2007Chapter in book (Other academic)
    Abstract [en]

    Circadian clocks are found in most eukaryotic organisms. By allowing anticipation of daily and seasonal changes they enable coordination of metabolism and life cycle with the natural rhythms of the environment. Plant circadian rhythms are generated by a series of interlocking feedback loops of ribonucleic acid (RNA) and protein expression that respond to environmental cycles of light and temperature. They control essential processes in the plant’s development, such as the transition to flowering or growth cessation.

  • 17.
    Michelson, Ingrid H.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ingvarsson, Pär K.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Robinson, Kathryn M.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Edlund, Erik
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Eriksson, Maria E.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Nilsson, Ove
    Jansson, Stefan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Autumn senescence in aspen is not triggered by day length2018In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 162, no 1, p. 123-134Article in journal (Refereed)
    Abstract [en]

    Autumn senescence in mature aspens, grown under natural conditions, is initiated at almost the same date every year. The mechanism of such precise timing is not understood but we have previously shown that the signal must be derived from light. We studied variation in bud set and autumn senescence in a collection of 116 natural Eurasian aspen (Populus tremula) genotypes, from 12 populations in Sweden and planted in one northern and one southern common garden, to test the hypothesis that onset of autumn senescence is triggered by day length. We confirmed that, although bud set seemed to be triggered by a critical photoperiod/day length, other factors may influence it. The data on initiation of autumn senescence, on the other hand, were incompatible with the trigger being the day length per se, hence the trigger must be some other light-dependent factor.

  • 18.
    Norén, Louise
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kindgren, Peter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Copenhagen Plant Science Centre, University of Copenhagen.
    Stachula, Paulina
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Rühl, Mark
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Eriksson, Maria E.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Hurry, Vaughan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Strand, Åsa
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Circadian and Plastid Signaling Pathways Are Integrated to Ensure Correct Expression of the CBF and COR Genes during Photoperiodic Growth2016In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 171, no 2, p. 1392-1406Article in journal (Refereed)
    Abstract [en]

    The circadian clock synchronizes a wide range of biological processes with the day/night cycle, and correct circadian regulation is essential for photosynthetic activity and plant growth. We describe here a mechanism where a plastid signal converges with the circadian clock to fine-tune the regulation of nuclear gene expression in Arabidopsis (Arabidopsis thaliana). Diurnal oscillations of tetrapyrrole levels in the chloroplasts contribute to the regulation of the nucleus-encoded transcription factors C-REPEAT BINDING FACTORS (CBFs). The plastid signal triggered by tetrapyrrole accumulation inhibits the activity of cytosolic HEAT SHOCK PROTEIN90 and, as a consequence, the maturation and stability of the clock component ZEITLUPE (ZTL). ZTL negatively regulates the transcription factor LONG HYPOCOTYL5 (HY5) and PSEUDO-RESPONSE REGULATOR5 (PRR5). Thus, low levels of ZTL result in a HY5- and PRR5-mediated repression of CBF3 and PRR5-mediated repression of CBF1 and CBF2 expression. The plastid signal thereby contributes to the rhythm of CBF expression and the downstream COLD RESPONSIVE expression during day/night cycles. These findings provide insight into how plastid signals converge with, and impact upon, the activity of well-defined clock components involved in circadian regulation.

  • 19.
    Norén, Louise
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Kindgren, Peter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Copenhagen Plant Science Centre, University of Copenhagen, Thorvaldsenvej 40, 1871 Frederiksberg, Denmark.
    Stachula, Paulina
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Rühl, Mark
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Eriksson, Maria E.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Hurry, Vaughan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Strand, Åsa
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    HSP90, ZTL, PRR5 and HY5 integrate circadian and plastid signaling pathways to regulate CBF and COR expressionManuscript (preprint) (Other academic)
  • 20.
    Takata, Naoki
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Eriksson, Maria E.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    A simple and efficient transient transformation for hybrid aspen (Populus tremula x P. tremuloides)2012In: Plant Methods, ISSN 1746-4811, E-ISSN 1746-4811, Vol. 8, p. 30-Article in journal (Refereed)
    Abstract [en]

    Background: The genus Populus is accepted as a model system for molecular tree biology. To investigate gene functions in Populus spp. trees, generating stable transgenic lines is the common technique for functional genetic studies. However, a limited number of genes have been targeted due to the lengthy transgenic process. Transient transformation assays complementing stable transformation have significant advantages for rapid in vivo assessment of gene function. The aim of this study is to develop a simple and efficient transient transformation for hybrid aspen and to provide its potential applications for functional genomic approaches. Results: We developed an in planta transient transformation assay for young hybrid aspen cuttings using Agrobacterium-mediated vacuum infiltration. The transformation conditions such as the infiltration medium, the presence of a surfactant, the phase of bacterial growth and bacterial density were optimized to achieve a higher transformation efficiency in young aspen leaves. The Agrobacterium infiltration assay successfully transformed various cell types in leaf tissues. Intracellular localization of four aspen genes was confirmed in homologous Populus spp. using fusion constructs with the green fluorescent protein. Protein-protein interaction was detected in transiently co-transformed cells with bimolecular fluorescence complementation technique. In vivo promoter activity was monitored over a few days in aspen cuttings that were transformed with luciferase reporter gene driven by a circadian clock promoter. Conclusions: The Agrobacterium infiltration assay developed here is a simple and enhanced throughput method that requires minimum handling and short transgenic process. This method will facilitate functional analyses of Populus genes in a homologous plant system.

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