Research Area
Environmental control of plant growth and development
Strategy
Experimentation and mathematical modelling
Background
In higher plants, the need to sense and interpret environmental light cues in a meaningful way has led to the evolution of highly sophisticated molecular signalling networks. Controlling these networks are families of photoreceptors whose collective action shapes growth and development via a process that is referred to as photomorphogenesis. Recent work in our lab has shown that light receptor pathways play a pivotal role in temperature signalling. We are currently employing a range of approaches to understand the molecular processes that integrate environmental light and temperature signals.
Projects
1. ROBuST: Regulation of Biological Signalling by Temperature
Even though global earth surface temperatures are predicted to rise over the coming century we know very little of how plants cope with temperature change. The BBSRC/EPSRC-funded ROBuST project seeks to understand the molecular circuitry that enables plants to react to or withstand sometimes extreme daily and seasonal temperature changes. To do this we are combining experimentation, computational modelling and mathematical approaches to establish how temperature modifies signalling through a central regulatory network. Our cross-disciplinary work programme has identified novel thermal signalling mechanisms, defined new hypotheses in silico that are tested in the lab, and determined general principles that underlie temperature signalling.
ROBuST collaborators: Dr Steve Penfield (University of Exeter), Dr Anthony Hall (University of Liverpool), Prof. David Rand and Dr Bärbel Finkenstädt (University of Warwick), Prof. Andrew Millar, Prof. Mathew Williams, Dr Stephen Gilmore (University of Edinburgh), Prof. Mike White (University of Manchester), Prof. Ian Graham (University of York).
2. The intersection of light, temperature and the plant body clock
This project is looking into the processes that control the timing of growth in the daily light/dark cycle. The rhythmic expression of two genes, PIF4 and PIF5, has been shown to underlie this temporal response. Figure 1 shows the timing and duration of the growth phase that are thought to be set by the combined impact of the plants internal pacemaker (the circadian clock) and external signals (light [yellow] and temperature [red]) on PIF4/PIF5 levels and activity. We are currently building mathematical models to test and expand our knowledge of this so called “external coincidence' mechanism that controls growth. Hypotheses that are determined from the models are tested experimentally and resulting new knowledge feeds back to inform model development.
Figure 1. Schematic of the external coincidence of Arabidopsis stem growth. Current knowledge of this system suggests that the development of the Arabidopsis stem is controlled through the transcription factors PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PIF5. These genes integrate pathways from the circadian clock and the external environment, notably light (yellow sun) and temperature (red bolt) signalling. PIF4/5 have been shown to be regulated by LUX ARRHYTHMO (LUX) from the circadian clock, whilst temperature increases the PIF mRNA abundance and light (through PHYB - the primary regulator of red light signals) inhibits the accumulation of protein.
3. Photothermal models
We are developing mathematical models that can simulate Arabidopsis plant growth and development to flowering under different field conditions (Figure 2). This approach considers the impact of plant genotype on externally-driven signals (i.e. light and temperature) that intercept with internal circadian oscillator to regulate floral timing. Our models can predict flowering time through the seasons, and are instructive educational tools.
Figure 2. Schematic diagram of our photothermal model. The model is made up of three components: (a) The photoperiod component, which is divided into three sections by two critical day lengths; (b) The thermal time component considers hourly temperatures above 3oC, with different effectiveness at day and night; (c) The vernalisation component, which has two sub-components. The modifier represents the extent of vernalisation, which depends on the accumulated vernalisation effectiveness at different temperatures within the range of -3.5 – 6.00C; (d) The Modified Photothermal Unit (MPTU) is a product of the three components. MPTU is accumulated every hour until a threshold value is reached to indicate reproductive switch.
Collaborators: Prof. Johanna Schmitt (Brown University RI, USA), Prof. Stephen Welch (Kansas State University, USA), Prof. Amity Wilczek (Deep Springs College NV, USA).
4. Dynamic properties of phytochrome B
The light receptor phyB exists in two states red (R)-absorbing inactive Pr form and a far-red (FR) active Pfr isoform. phyB has been described as a biological light switch as R triggers the photoconversion of Pr to its active Pfr isoform, while FR switches it back. However, as Pr and Pfr have broadly-overlapping absorption spectra (see Figure 3) most wavelengths in the red to far-red range establish a dynamic equilibrium of Pr:Pfr. We are interested in how changes in the light and temperature environment affect the dynamic properties of phyB. As phyB is a potent plant growth regulator, this knowledge will help us understand how the local habitat and the seasons affect plant growth strategy.
Figure 3. Absorption Spectra from the inactive (Pr) and active (Pfr) forms of phytochrome plotted as a percentage of the maximum peak of Pr. (adapted from Maninelli Photomorphogenesis in Plants R.E. Kendrick and G.M.H. Kronenberg, eds.1994) The peak of absorbance occurs for Pr at 666nm and for Pfr at 730nm. Data adapted from Mancinelli, A.L. (1994).
Collaborators: Dr Christian Fleck (University of Freiburg, Germany), Dr Stefan Kircher (University of Freiburg, Germany), Dr Ramon Grima (University of Edinburgh, UK)
5. Signal Integration
The plant life cycle is intimately connected to the external environment. For example, light and temperature signals provide vital seasonal cues that control the timing of key developmental events such as germination or flowering. But how do plants interpret the variety of signals to which they are exposed on a daily basis? This project explicitly considers the decision-making molecular circuitry that integrates different environmental signals. We have recently described a dual-input signalling motif that has a critical role in maintaining plant growth as ambient temperatures rise (Figure 4).
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Figure 4. Light signalling networks are essential for buffering the effects of warm temperatures. An increase in temperature promotes elongated growth of hypocotyl and petioles, while light generally inhibits elongation. Removal of a major photoreceptor (phyB) and HFR1 (a positive factor in light singalling) has a dramatic effect at high temperatures, illustrating that light singalling is vital to control plant growth in the warm. 3 week old plants grown in diurnal white light (12:12). Scale bar = 10mm. |
Collaborator: Prof. Christian Fankhauser (University of Lausanne, Switzerland)