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David Somers

David SomersDr. David Somers
Associate Professor
Ph.D., University of California at Berkley, 1994.

Contact:
The Ohio State University
Plant Cellular and Molecular Biology
206 Rightmire Hall
1060 Carmack Road
Columbus, OH 43210

Office: Office: 614.292.2551
Laboratory: 614.292.2533
Fax: 614.292.5379
e-Mail: Somers.24@osu.edu

Focus:

Molecular and genetic analysis of the plant circadian system.

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, such as flowering time, 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.

The central pacemaker driving circadian rhythms in plants consists of one or more autoregulatory feedback loops that are still being molecularly dissected. Work in my lab focuses on the intersection of light input to the clock and the molecular components that comprise the oscillator.

ZEITLUPE (ZTL) is an F-box protein originally isolated as a long period mutant in Arabidopsis. It, and two related family members, are unique among the nearly 700 plant F-box proteins in possessing a blue-light sensing LOV (Light Oxygen and Voltage) domain at its N-terminus, very similar to the flavin-binding regions found in the phototropins. ZTL targets at least two members of a closely related family of pseudoresponse regulators that are key in setting the pace of the oscillator. Our work with ZTL has focused on understanding the role of each of three domains that comprise the protein, in the context of the circadian system. We have recently identified ZTL as a novel blue light photoreceptor, the first F-box protein to possess this property. Interestingly, light absorption appears necessary to sustain ZTL levels, meaning photoperception is largely an act of self-preservation. The mechanism of this property and the consequences for clock function is part of our focus.

Recently we have identified an interactor with ZTL that regulates its stability in vivo. GIGANTEA (GI) was first identified 40 years ago as a regulator of flowering time. Since then, further characterization of gi mutants has demonstrated a wide-ranging role for the protein throughout plant development, including control over circadian period.  The subsequent cloning of the GI gene provided little insight into its function. Our demonstration that GI is necessary to confer post-translational control of circadian cycling to ZTL protein both identified a molecular role for GI and uncovered a new post-translational mechanism of establishing a circadian rhythm in eukaryotes (see Figure). We are pursing further the biochemical function of GI to understand the primary basis of its action, as well as its larger role in plant developement.

 

Post-translational control of circadian cycling through cooperative stabilization of ZTL and GI.

Post-translational control of circadian cycling through cooperative stabilization of ZTL and GI.

(a) mRNA levels of GI (gray line) are rhythmic under LD  in contrast to constitutive expression of ZTL mRNA (blue). Clock-controlled GI mRNA rhythms results in GI protein, which interacts with ZTL. Cooperative stabilization increases levels of ZTL and GI proteins, with enhancement of the interaction in the light by blue light photoactivation of ZTL (bolt), and a diminished interaction in the dark. This results in robust oscillations of both proteins. (b) One consequence of ZTL oscillations is to refine or “sculpt” the TOC1 protein profile (red line). In the absence of GI (-GI) ZTL levels are very low and non-cyclic. TOC1 protein oscillates with low amplitude, tracking its own message rhythms. In the WT (GI+), ZTL protein rhythms lead to high amplitude TOC1 protein cycles, resulting in a normal circadian period and phasing of clock-controlled outputs.

Teaching:

Lab Members:

Undergraduates

Postdoctorates

Lab Alumni:

Selected publications (2000 - Date):

  1. Fujiwara, S., Wang, L., Han, L., Suh, S. S., Salome, P. A., McClung, C. R., Somers, D. E. (2008). Post-translational regulation of the Arabidopsis circadian clock through selective proteolysis and phosphorylation of pseudo- response regulator proteins. J.Biol.Chem. 283: 23073-23083

  2. Jin JB, Jin YH, Lee J, Miura K, Yoo CY, Kim WY, Van Oosten M, Hyun Y, Somers DE, Lee I, Yun DJ, Bressan RA, Hasegawa PM. 2008. The SUMO E3 ligase, AtSIZ1, regulates flowering by controlling a salicylic acid-mediated floral promotion pathway and through affects on FLC chromatin structure. Plant J. 53(3):530-540

  3. Kim, W.Y, Fujiwara, S., Suh, S.S., Kim, J., Kim, Y., Han, L., David, K., Putterill, J.,  Nam. H.G., and Somers, D.E. 2007. ZEITLUPE is a circadian photoreceptor stabilized by GIGANTEA in blue light. Nature 449: 356-360.

  4. Allen T., Koustenis A., Theodorou G.,Somers, D.E., Kay S.A., Whitelam G.C., Devlin P.F. (2006) Arabidopsis FHY3 specifically gates phytochrome signaling to the circadian clock. Plant Cell 18: 2506-2516[pdf]

  5. Kevei,E., Gyula,P., Hall,A., Kozma-Bognar,L., Kim,W.Y., Eriksson,M.E., Toth,R., Hanano,S., Feher,B., Southern,M.M., Bastow,R.M., Viczian,A., Hibberd,V., Davis,S.J.,Somers, D.E., Nagy,F., and Millar,A.J. (2006) Forward genetic analysis of the circadian clock separates the multiple functions of ZEITLUPE. Plant Physiol 140:933-945 [pdf]

  6. Kim, W.Y., Hicks, K. A. and Somers, D.E. 2005. Independent roles for EARLY FLOWERING 3 and ZEITLUPE in the control of circadian timing, hypocotyl length, and flowering time. Plant Physiol. 139:1557-69. [pdf]

  7. Han, L., Mason, M., Risseeuw, E.P., Crosby, W.L. and Somers, D.E. 2004. Formation of an SCFZTL complex is required for proper regulation of circadian timing. Plant J. 40: 291-301. [pdf]

  8. Somers, D.E., Kim,W.Y., and Geng, R. 2004. The F-Box protein ZEITLUPE confers dosage-dependent control on the circadian clock, photomorphogenesis, and flowering time. Plant Cell 16: 769-782. [pdf]

  9. Mas P., Kim WY, Somers D.E., and Kay S.A. 2003. Targeted degradation of TOC1 by ZTL modulates circadian function in Arabidopsis thaliana. Nature. 426:567-70. [pdf]

  10. Kim, W.Y., Geng, R., and Somers, D.E. 2003. Circadian phase-specific degradation of the F-box protein ZTL is mediated by the proteasome. Proc Natl Acad Sci U S A 100(8): 4933-4938. [pdf]

  11. Risseeuw, E.P., Daskalchuk, T.E., Banks, T.W., Liu, E., Cotelesage, J., Hellmann, H., Estelle, M., Somers, D.E., and Crosby, W.L. 2003. Protein interaction analysis of SCF ubiquitin E3 ligase subunits from Arabidopsis. Plant J. 34(6):753-767. [pdf]

  12. Somers, D.E., Schultz, T.F., Milnamow, M. and Kay S.A. 2000. ZEITLUPE encodes a novel clock associated PAS protein from Arabidopsis. Cell 101: 319-329. [pdf]

  13. Strayer C., Oyama T., Schultz T.F., Raman R., Somers D.E., Mas P., Panda S., Kreps J.A., Kay S.A. 2000. Cloning of the Arabidopsis clock gene TOC1, an autoregulatory response regulator homolog. Science. 289:768-71.

Invited Publications, Book Chapters and Reviews (2000-present)

 

  1. Somers, D. E., Fujiwara, S., Kim, W. Y., Suh, S. S. (2007). Post-translational photomodulation of circadian amplitude. Cold Spring Harb. Symp. Quant. Biol. 72: 193-200

  2. Somers, D.E. 2005. Entrainment of the Circadian Clock. In: Endogenous Plant Rhythms, eds. Hall, A.J.W and McWatters, H.G., Oxford: Blackwell, pp. 85-105

  3. Somers, D.E. 2005. ZEITLUPE and the Control of Circadian Timing. In: Light Sensing in Plants, eds.Wada, M., Shimazaki, K., and Iino, M., Tokyo: Springer, pp. 347-354..

  4. Somers, D.E. 2003. Photobiology of Circadian Rhythms. In: CRC Handbook of Organic Photochemistry and Photobiology, 2nd Edition, William Horspool and Francesco Lenci, eds.

  5. Somers, D.E. 2001. Clock-associated genes in Arabidopsis: a family affair. Philos Trans R Soc Lond B Biol Sci. 356:1745-53. [pdf]

Revised: 12-aug-08

PCMB NEWS

Work Study Position Available in PCMB

8-20 hrs/week; $7.26-8.25/hour.
Contact Dr. Rebecca Lamb.
Position Information [pdf}

A MDA (Muscular Dystrophy Association) sponsored post-doctoral position is available in the Department of Plant Cellular and Molecular Biology/Molecular and Cellular Biochemistry at Ohio State University in Columbus, Ohio, starting on August 1st 2008.

The researcher will work in the field of mitochondria biogenesis and study the assembly process of c-type cytochromes, a class of hemoproteins with covalent attachment of the heme co-factor to a CXXCH motif on the apocytochrome. Cytochromes c are versatile molecules that function in electron transfer reactions but also in signaling the death pathways. Their assembly process is not understood and in humans mutations in the only known cytochrome c assembly factor cause a neurodevelopmental disease with cardiomyopathic manifestations.

The future hire will use yeast as an experimental system and focus on 1) elucidating the biochemical activity of Cyc2p a novel mitochondrial flavoprotein that controls a yet-to-be-defined redox step in the heme attachment reaction to apocytochrome and 2) identifying additional mammalian cytochrome-c assembly factors. Because we suspect a role of Cyc2p in thiol-based chemistry, the researcher will also take part in on-going genetic experiments to 3) further dissect the pathway(s) that operate in intermembrane thiol-based redox chemistry. Thiol-based chemistry in the mitochondrial intermembrane space is a recent and novel development in the field since the discovery of catalysts that promote disulfide bond formation. Molecular genetics and biochemical approaches will be used to answer the scientific questions we are interested in. Interested candidates should send a cover letter, resume, and a list of three referees to Dr. Patrice Hamel at hamel.16@osu.edu. Use Post-doctoral Position in the subject line. For additional information, see also Dr. Hamel's Web Site.

Erich Grotewold Receives Grant from US-Israeli Binational Agricultural Research and Development Fund

We are pleased to announce that Erich Grotewold has been awarded another new grant. This is a 3-year award from the US-Israeli Binational Agricultural Research and Development Fund. It is in the amount of $137,000 and is entitled "Regulation of tomato fruit development by interacting MYB proteins."

Erich Grotewold Receives DOE And NSF Grants

Erich Grotewold has been awarded 3-year grant in the amount o $449,390 from the DOE, entitled "Engineering phenolic metabolism in the grasses using transcription factors."

Erich has also been awarded a second, major grant from NSF (Plant Genome). It is a 3-year award in the amount of $2,479,632 entitled "The Grass Regulome Initiative: Integrating control of gene expression and agronomic traits across the grasses.

David Somers' Lab Published In Nature

David Somers’ group has published an article in Nature (Sept. 20) entitled, “ZEITLUPE is a circadian photoreceptor stabilized by GIGANTEA in blue light.” Woe-Yeon Kim and Sumire Fujiwara are co-first authors.

Erich Grotewold Awarded USDA Grant

Erich Grotewold has been awarded a grant from the USDA in the amount of $201,025 for a two-year study entitled, “Transposons as gene control elements.”

Rebecca Lamb Receives OPBC Award

Rebecca Lamb has received an award of $57,567 over two years from the OPBC for a study entitled, ”Two Arabidopsis WWE-PARP proteins involved in abiotic stress response and development.”

Plant Biotechnology In-Floor Seminar Series Schedule

Follow the link below for a schedule of informal 30-40 min seminars that will take place at noon on Fridays in room 189 of Rightmire Hall.
Schedule [pdf]

News Archive

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