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.
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.
In 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.
In 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.
Samanfattning på Svenska
- Edwards KD, Takata N, Johansson M, Jurca M, Novák O, Hényková E, Liverani S, Kozarewa I, Strnad M, Millar AJ, Ljung K, Eriksson ME (2018) Circadian clock components control daily growth activities by modulating cytokinin levels and cell division-associated gene expression in Populus trees. Plant Cell & Environment on-line 8 March 2018
- Johansson M, McWatters HG, Bakó L, Takata N, Gyula P, Hall A, Somers DE, Millar AJ, Eriksson ME (2011). Partners in time: EARLY BIRD associates with ZEITLUPE and regulates the speed of the Arabidopsis clock. Plant Physiology: 155:2108-2122
- Ashelford K, Eriksson ME, Allen CM, D’Amore L, Johansson M, Gould P, Kay S, Millar AJ, Hall N, Hall A (2011). Full genome re-sequencing reveals a novel circadian clock mutation in Arabidopsis. Genome Biology: 12:R28, 12 pp
- Ibáñez C, Kozarewa I, Johansson M, Ögren E, Rohde A, Eriksson ME (2010). Circadian clock components regulate entry and affect exit of seasonal dormancy as well as winter hardiness in Populus trees. Plant Physiology: 153:1823-1833
- Kozarewa I, Ibáñez C, Johansson M, Ögren E, Mozley D, Nylander E, Chono M, Moritz T, Eriksson ME (2010). Alteration of PHYA expression change circadian rhythms and timing of bud set in Populus. Plant Molecular Biology: 73:143-156
- Eriksson ME, Hanano S, Southern MM, Hall A, Millar AJ (2003). Response regulator homologues have complementary, light- dependent functions in the Arabidopsis circadian clock. Planta: 218:159-162
- Eriksson ME, Israelsson M, Olsson O, Moritz T (2000). Increased gibberellin biosynthesis in transgenic trees promotes growth, biomass production and xylem fiber length. Nature Biotechnology 18:784-788