Main focus of my research is to understand the functional aspects of the circadian clockwork in Arabidopsis and hybrid aspen (Populus sp.), and how this timing machinery influences the regulation of growth. We use both the annual Arabidopsis and the deciduous Populus to address these questions using forward and reverse genetics approaches.

Ericsson Maria 1150
To anticipate the diurnal cycle of light and dark, most organ- isms have developed a molecular time measuring system called a circadian (circadian lat.= about a day) oscillator or clock. It re-sets to local time on a daily basis and synchronizes the or- ganism's cellular and physiological events to its most favorable time of the day. It is also implicated in seasonal events such as flowering and bud set in trees, in order for them to occur at the most favorable time of year. Moreover, we have shown that a functional clock is essential for seasonal timing, cold response and freezing tolerance of Populus trees. Hence, if we learn more about temporal regulation, there is therefore a great potential for biotechnological application in adapting new plants or re-adapting (in case of climate warming) local plants to local conditions to increase the length of the growth season and to keep winter hardiness.
Light is received by multiple photoreceptors in the red, far red and blue spectra and mediates re-setting of the circadian clock, while temperature may be received directly by central components of the clock.

maria e 1Luciferase imaging of Populus cuttingsIn Arabidopsis there are five red/far-red light photoreceptors, phytochromes (phy); the best characterized are phyA (far red) and phyB (red). In the blue wavelengths receptors like the cryptochromes (cry1 and cry2) are important, but also members of the ZEITLUPE (ZTL) gene family, of F-box, Kelch-, and LOV/PAS domain containing proteins are thought capable of receiving blue light directly and are involved in regulation of the circadian clock and seasonal timing.
The most central clock proteins are TIMING OF CAB2 EXPRESSION 1 (TOC1), CIRCADIAN CLOCK ASSOCI- ATED1 (CCA1), and LATE ELONGATED HYPOCOTYL (LHY) forming a feedback loop where the two single myb domain proteins CCA1 and LHY negatively regulates the expression of the pseudo-response regulator (PRR) TOC1. However, their regulation repressor is intertwined with at least two additional interlocked feedback loops.

maria_e_3Signs of season. An apex of Populus in active growth (upper left), at bud set (upper right), during dormancy (lower right) and at bud burst (lower left).IIn order to find clock associated genes, mutant approaches in Arabidopsis have been very fruitful.A true clock mutant needs to be affected in several out-puts from the clock, and have to have an effect on genes found close to the central loops.Tracking the movements of leaves or expression from promoters under circadian control under constant conditions, like the hands of a mechanical clock, make it possible to tell the pace and features of the inner clock's rhythm and to characterize new clock mutants. We use the Arabidopsis clock as a model that is now explored further in the deciduous perennial setting using Populus.
In order to study the clockwork and its adaptive value, we use Arabidopsis or hybrid aspen lines with altered levels of clock gene expression, and molecular tools such as promoter:LUCIF- ERASE expression, and real time PCR to monitor circadian clock regulated gene expression.To investigate perennial growth, we monitor elongation growth and physiological manifestations of season such as flowering, growth cessation, bud set and bud break. Mutants with an altered timing mechanism help us to build a model for clock function and its impact on seasonal regulation of growth in this species. Clock mutants also offer a possibility to further the understanding of the clock's role in the life of a plant, and its impact on metabolism and the synthesis of plant hormones that regulate growth on a daily basis.
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Publication list

  1. Growing in time: Exploring the molecular mechanisms of tree growth
    Tree Physiol. 2020 May 29 [Epub ahead of print]
  2. GIGANTEA-like genes control seasonal growth cessation in Populus
    New Phytol. 2018, 218 (4):1491-1503
  3. Circadian clock components control daily growth activities by modulating cytokinin levels and cell division-associated gene expression in Populus trees
    Plant Cell Environ. 2018, 41 (6):1468-1482
  4. Autumn senescence in aspen is not triggered by day length
    Physiol Plant. 2018, 162(1):123-134
  5. Circadian and Plastid Signaling Pathways Are Integrated to Ensure Correct Expression of the CBF and COR Genes during Photoperiodic Growth
    Plant Physiol. 2016, 171(2):1392-1406
  6. Plant Circadian Rhythms -based in part on the version published 2007
    eLS, 1-10 2016
  7. Role of the circadian clock in cold acclimation and winter dormancy in perennial plants
    In "Advances in dormancy", 2015, Ed Anderson J, Springer New York
  8. Transgenic hybrid aspen trees with increased gibberellin (GA) concentrations suggest that GA acts in parallel with FLOWERING LOCUS T2 to control shoot elongation
    New Phytologist 2015, 205(3):1288-95
  9. The perennial clock is an essential timer for seasonal growth events and cold hardiness
    Plant Circadian Networks, 297-311 2014
  10. Monitoring seasonal bud set, bud burst, and cold hardiness in Populus
    Plant Circadian Networks, 313-324 1 2014
  11. Takata N, Eriksson ME
    A simple and efficient transient transformation for hybrid aspen (Populus tremula × P. tremuloides)
    Plant Methods 2012, 8:30
  12. Cooke JE, Eriksson ME, Junttila O
    The Dynamic Nature of Bud Dormancy in Trees: Environmental Control and Molecular Mechanisms
    Plant Cell Environ. 2012 10(35):1707-1728
  13. Plant cell responses to cold are all about timing
    Curr Opin Plant Biol. 2011 Dec;14(6):731-7
  14. Ashelford K, Eriksson ME, Allen CM, D'Amore L, Johansson M, Gould P, Kay S, Millar AJ, Hall N, Hall A
    Full genome re-sequencing reveals a novel circadian clock mutation in Arabidopsis
    Genome Biology: 2011 12:R28, 12 pp
  15. Johansson M, McWatters HG, Bakó L, Takata N, Gyula P, Hall A, Somers DE, Millar AJ, Eriksson ME
    Partners in time: EARLY BIRD associates with ZEITLUPE and regulates the speed of the Arabidopsis clock
    Plant Physiology: 2011 155:2108-2122
  16. Ibáñez C, Kozarewa I, Johansson M, Ögren E, Rohde A, Eriksson ME
    Circadian clock components regulate entry and affect exit of seasonal dormancy as well as winter hardiness in Populus trees
    Plant Physiology: 2010 153:1823-1833
  17. Kozarewa I, Ibáñez C, Johansson M, Ögren E, Mozley D, Nylander E, Chono M, Moritz T, Eriksson ME
    Alteration of PHYA expression change circadian rhythms and timing of bud set in Populus
    Plant Molecular Biology: 2010 73:143-156
  18. Hoffman DE, Jonsson P, Bylesjö M, Trygg J, Antti H, Eriksson ME, Moritz T
    Changes in diurnal patterns within the Populus transcriptome and metabolome in response to photoperiod variation
    Plant, Cell & Environment: 2010 33:1298-1313
  19. Plant Circadian Rhythms
    eLS 2007
  20. Kevei E, Gyula P, Hall A, Kozma-Bognar L, Kim WY, Eriksson ME, Toth R, Hanano S, Feher B, Southern MM, Bastow RM, Viczian A, Hibberd V, Davis SJ, Somers DE, Nagy F, Millar AJ
    Forward genetic analysis of the circadian clock separates the multiple functions of ZEITLUPE
    Plant Physiology: 2006 140:933-945
  21. Israelsson M, Eriksson ME, Hertzberg M, Aspeborg H, Nilsson P, Moritz T
    Changes in gene expression in the wood-forming tissue of transgenic hybrid aspen with increased secondary growth
    Plant Mol Biol: 2003 52:893-903
  22. Eriksson ME, Millar AJ
    The circadian clock. A plant's best friend in a spinning world
    Plant Physiol: 2003 132:732-738
  23. Eriksson ME, Hanano S, Southern MM, Hall A, Millar AJ
    Response regulator homologues have complementary, light-dependent functions in the Arabidopsis circadian clock
    Planta: 2003 218:159-162
  24. Eriksson ME, Moritz T
    Daylength and spatial expression of a gibberellin 20-oxidase isolated from hybrid aspen (Populus tremula L. x P. tremuloides Michx.)
    Planta: 2002 214:920-930
  25. Eriksson ME, Israelsson M, Olsson O, Moritz T
    Increased gibberellin biosynthesis in transgenic trees promotes growth, biomass production and xylem fiber length
    Nature Biotechnology 2000 18:784-788
  26. Olsen JE, Junttila O, Nilsen J, Eriksson ME, Martinussen I, Olsson O, Sandberg G, Moritz T
    Ectopic expression of oat phytochrome A in hybrid aspen changes critical daylength for growth and prevents cold acclimatization
    Plant Journal: 1997 12:1339-1350
  27. Eriksson ME, Moritz T
    Isolation of a cDNA Encoding a Phytochrome A (Accession No.AJ001318) from Populus tremula x tremuloides. (PGR97-186)
    Plant Physiology: 1997 115:1731-1731