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David Somers Assistant Professor |
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Research Interests
The timing of many physiological and developmental processes in most eukaryotes is under the control of a circadian clock. This endogenous, self-sustaining oscillator maintains a rhythm of ca. 24 h in processes as diverse as human sleep/wake cycles, insect pupal eclosion, fungal sporulation and the movement of plant leaves. Many of the key events in plant development depend on receiving the appropriate environmental signals at the right time, and the circadian timekeeping mechanism allows them to keep pace with and anticipate cyclic events in their environment.
Work in my lab focuses on two aspects of the circadian clock in plants. The first is to understand the components and processes involved in the transduction of the daily environmental light/dark cycle to the central oscillator of the clock. Using the model genetic system of Arabidopsis thaliana, we have shown that two of the major red light (phytochromes) and blue light (cryptochromes) photoreceptor families in this plant are important in mediating light input to the clock. The next step will be to identify components downstream of these receptors that specifically signal to the oscillator.
My second interest is to understand the molecular nature of the central clock oscillator and how it is coupled to the light input pathway. We are exploiting transgenic Arabidopsis expressing firefly luciferase which has created a novel bioluminescent phenotype. The promoter of the gene coding for the chlorophyll a/b binding protein 2 (CAB2), driving luciferase expression (CAB2-luc), can accurately report the temporal and spatial expression patterns of the endogenous CAB2 gene to obtain accurate and reproducible estimates of the period, phase and amplitude of cyclic transcription driven by the circadian clock. Using this reporter, mutants with an abnormally longer period have been identified by imaging individual plants with a sensitive low-light video system. This assay has allowed the characterization of these long-period mutants to position them uniquely within the circadian system. All the mutations lie within a single gene and post-cloning work will focus on characterizing the role of the protein within the circadian system, as well as identifying genetic and biochemical interactors. The uniquely circadian phenotype of these mutants, which look morphologically wild-type, suggests they will serve as a excellent entry point towards the elucidation of the molecular basis of the clock in plants.
Selected References
- Park D.H., Somers D.E., Kim Y.S., Choy Y.H., Lim H.K., Soh M.S., Kim H.J., Kay S.A., Nam H.G. 1999. Control of circadian rhythms and photoperiodic flowering by the Arabidopsis GIGANTEA gene. Science. 285: 1579-1582.
- Somers, D.E. Devlin, P.A. and Kay, S.A. 1998. Phytochromes and cryptochromes in the entrainment of the Arabidopsis circadian clock. Science 282: 1488-1490.
- Somers, D.E., Webb, A., Pearson, M., and Kay, S.A. 1998. The short-period mutant, toc1-1, alters circadian clock regulation of multiple outputs throughout development in Arabidopsis thaliana. Development 125: 485-494.
- Anderson, S.L., Somers, D.E., Millar, A.J., Hanson, K., Chory, J. and Kay, S.A. 1997. Attenuation of phytochrome A and B signaling pathways by the Arabidopsis circadian clock. Plant Cell 9: 1727-1743.
- Devlin, P.F., Somers, D.E., Quail, P.H., and Whitelam, G.C. 1997. The Brassica rapa elongated internode (EIN) gene encodes phytochrome B. Plant Mol.Biol:. 34:537-547.
- Hicks, K.A., Millar, A.J., Carre, I.A., Somers, D.E., Straume, M., Meeks-Wagner, D.R. and Kay, S.A. 1996. Conditional circadian dysfunction of the Arabidopsis early-flowering 3 mutant. Science 274: 790-792.
- Somers, D.E. and Quail, P.H. 1995. Phytochrome-mediated light regulation of PHYA- and PHYB-GUS transgenes in Arabidopsis thaliana seedlings. Plant Physiol. 107: 523-534.
- Somers, D.E. and Quail, P.H. 1995. Temporal and spatial expression patterns of PHYA and PHYB genes in Arabidopsis. Plant J. 7: 413-427.
- Dehesh, K., Franci, C., Sharrock, R.A., Somers, D.E., Welsh J. and Quail, P.H. 1994. The Arabidopsis phytochrome A gene has multiple transcription start sites and a promoter sequence motif homologous to the repressor element of monocot phytochrome A genes. Photochem. Photobiol. 59: 379-384.
Book Chapters and Reviews
- Somers, D.E. 1999. The physiology and molecular bases of the plant circadian clock. Plant Physiol. 121: 9-20.
- Somers, D.E., and Kay, S.A. 1998. Genetic approaches to the analysis of circadian rhythms in plants. In: Biological Rhythms and Photoperiodism in Plants. eds. P. Lumsden and A.J. Millar. BIOS Scientific, Oxford.
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