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Room 2123
Department of Plant Biology
1002 Life Sciences, One Shields Ave.
University of California Davis
Davis, CA 95616

Contact: slharmer at

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  • A nice description of our recent article investigating the role of the clock in sunflower solar tracking and flower orientation can be found in this New Scientist article.
  • Links to additional popular press articles, podcasts, and social media references to this work may be found on this page.


Many organisms, including some prokaryotes and most eukaryotes, possess an internal timer or circadian clock that allows them to regulate their physiology to better adapt to our continually changing world. These circadian clocks generate roughly 24 hour rhythms in physiology and behavior that are maintained even in the absence of environmental cues. Although the molecular components of circadian clocks are not conserved across higher taxa, in all organisms studied these clocks are cell autonomous oscillators and in diverse eukaryotes are composed of complex transcriptional networks. As rooted organisms living in a continually changing world, plants are masters at withstanding environmental variation. The circadian clock is key: it both ensures the optimal timing of daily and seasonal events to cope with predictable stresses and regulates myriad signaling pathways to optimize responses to environmental cues. The study of circadian rhythms in plants thus presents a wide range of fascinating questions with real-world applications: What is the molecular nature of the circadian clock; that is, how can a cell keep time? What aspects of physiology are under circadian regulation? What are the mechanistic links between the clock network and other signaling pathways? Why does a functional circadian clock provide an adaptive advantage? The Harmer lab is using Arabidopsis thaliana and sunflower to address these important questions. We use forward and reverse genetics, genomics, biochemistry, and physiological studies to better understand the nature of the plant clock and how it helps shape plant responses to the environment.


Lab Members

Undergrad & high school interns

  • Faith Ajayi
  • Ben Caswell
  • Marcus Gainer
  • Emma Goguen
  • Tatiana Gromova
  • Leandro Guerrero
  • Nicky Kwa
  • Joe Martin
  • Valeria Nunez
  • Ryleigh Rupe
  • Yanne Santos
  • Bryant Tran

Former Members


Recent Publications

  • Atamian, H.S., Creux, N.M., Brown, E.A., Garner, A.G., Blackman, B.K., and Harmer, S.L. (2016) Circadian regulation of sunflower heliotropism, floral orientation, and pollinator visits. Science. 353(6299):587-90. doi: 10.1126/science.aaf9793 [1]
  • Atamian, H.S. and Harmer, S.L. (2016) Circadian regulation of hormone signaling and plant physiology. Plant Mol Biol. 91(6):691-702. doi: 10.1007/s11103-016-0477-4 [2]
  • Jones, M.A., Hu, W., Litthauer, S., Lagarias, J.C. and Harmer, S.L. (2015) A constitutively active allele of phytochrome B maintains circadian robustness in the absence of light. Plant Physiology. 169(1):814-25. doi: 10.1104/pp.15.00782 [3]
  • Anver, S., Roguev, A., Zofall, M., Krogan, N.J., Grewal, S.I.S., and Harmer, S.L. (2014) Yeast X-Chromosome Associated Protein 5 (Xap5) Functions with H2A.Z to Suppress Aberrant Transcripts. EMBO reports. pii: e201438902. [4]
  • Hsu, P.Y. and Harmer, S.L. (2013) Wheels within wheels: the plant circadian system. Trends in Plant Science [5]
  • Hsu, P.Y., Devisetty, U.K., and Harmer, S.L. (2013) Cycling activators control the evening arm of the plant clock. eLife. 2:e00473. [6]
  • Zemach, A., Kim, M.Y., Hsieh, P.-H., Coleman-Derr,D., Eshed-Williams, L., Thao, K, Harmer, S.L., and Zilberman, D. (2013) The Arabidopsis nucleosome remodeler DDM1 allows DNA methyltransferases to access H1-containing heterochromatin. Cell 153(1):193-205 [7]
  • Hu, W., Franklin, K.A., Sharrock, R.A., Jones, M.A., Harmer, S.L., and Lagarias, J.C. (2013) Unanticipated regulatory roles for Arabidopsis phytochromes revealed by null mutant analysis. Proceedings of the National Academy of the Science 110(4) 1542-1547. [8]
  • Hsu, P.Y. and Harmer, S.L. (2012) Circadian phase has profound effects on differential expression analysis. PLoS One 7(11):e49853 [9]
  • Jones, M.A., Williams, B.A., McNicol J., Simpson, C.G., Brown, J.W., and Harmer, S.L. (2012) Mutation of Arabidopsis SPLICEOSOMAL TIMEKEEPER LOCUS 1 causes circadian clock defects. Plant Cell, 24(10):4066-82 [10]


Blackman Lab
Jones Lab
Lagarias Lab
Maloof Lab
Montemurro Lab
Yanovsky Lab

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