Organisms that fail to respond appropriately to seasonal change will face severe consequences related to survival and reproduction. For humans, seasonal variation in the amount of light causes Seasonal Affective Disorder (SAD), a recurrent subtype of depression. Although the molecular mechanisms underlying SAD remain elusive, it is known that photoperiodic mechanisms play a significant role in many cases of SAD. Many organisms, including humans, have evolved mechanisms to sense changes in day length (=photoperiod) and integrate seasonal change information into their development. The long-term goal of our research program is to elucidate the molecular mechanisms by which organisms measure changes in day length and adjust their behaviors and development accordingly. Although the molecular mechanisms of photoperiodism have not yet been well described in many organisms, recent advances in the study of the model plant Arabidopsis have increased our molecular understanding of photoperiodic time measurement and have influenced the study of other plant and animal species. In Arabidopsis, the core time-measurement mechanism is circadian-regulated transcription of the floral activator CONSTANS (CO) gene and light-regulated CO protein stability and activity. In this proposal, further characterization o this core mechanism will be done through biochemical, genetic, and genomic approaches.
In Aim 1, newly identified transcriptional regulators of CO will be characterized. The findings will elucidate further how the circadian clock plays a role in regulating seasonal response by orchestrating different classes of transcription factors.
In Aim 2, time-dependent chromatin modification of CO transcriptional regulation - a new mechanistic layer of understanding - will be studied. Our previous results indicated the involvement of the FKF1 blue-light photoreceptor in posttranslational regulation of CO protein.
In Aim 3, the molecular function of FKF1-associating proteins on CO protein stability regulation will be examined. With these three Aims, the mechanisms by which plants monitor daily and seasonal differences through the circadian clock will be analyzed. The findings will impact plant research and our broader understanding of photoperiodism and circadian clocks in mammals and other systems. The types of transcriptional and posttranslational mechanisms present in Arabidopsis are likely conserved among all eukaryotes, thus these findings will contribute to our understanding of fundamental transcriptional regulation. These findings also have the potential to provide clues to the mechanisms involved in SAD. Finally, elucidating the photoperiodic flowering mechanism is important for understanding a major plant reproduction mechanism that is directly applicable to improvements in crop yield, an important contributor to human health especially in developing countries.

Public Health Relevance

Failure to adapt to seasonal change can have critical impacts on an organism's survival and reproductive success, and on human behavior. This proposed research, regarding the molecular mechanisms of day-length measurement in plants, will be important for plant research and for a broader understanding of photoperiodism and circadian clock-regulated behaviors in mammals and other organisms. In addition, elucidating this mechanism is essential for understanding a major plant reproduction mechanism, one that is directly applicable for improvement of crop yield (an important contributor to human health, especially in developing countries) and to our understanding of a sophisticated, time-resolved transcriptional mechanism that is universal and fundamental among all eukaryotes.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular Genetics B Study Section (MGB)
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Sesma, Michael A
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University of Washington
Schools of Arts and Sciences
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Song, Young Hun; Ito, Shogo; Imaizumi, Takato (2013) Flowering time regulation: photoperiod- and temperature-sensing in leaves. Trends Plant Sci 18:575-83
Liu, Hongtao; Wang, Qin; Liu, Yawen et al. (2013) Arabidopsis CRY2 and ZTL mediate blue-light regulation of the transcription factor CIB1 by distinct mechanisms. Proc Natl Acad Sci U S A 110:17582-7
Kinmonth-Schultz, Hannah A; Golembeski, Greg S; Imaizumi, Takato (2013) Circadian clock-regulated physiological outputs: dynamic responses in nature. Semin Cell Dev Biol 24:407-13
Ito, Shogo; Song, Young Hun; Josephson-Day, Anna R et al. (2012) FLOWERING BHLH transcriptional activators control expression of the photoperiodic flowering regulator CONSTANS in Arabidopsis. Proc Natl Acad Sci U S A 109:3582-7
Song, Young Hun; Lee, Ilha; Lee, Sang Yeol et al. (2012) CONSTANS and ASYMMETRIC LEAVES 1 complex is involved in the induction of FLOWERING LOCUS T in photoperiodic flowering in Arabidopsis. Plant J 69:332-42
Ito, Shogo; Song, Young Hun; Imaizumi, Takato (2012) LOV domain-containing F-box proteins: light-dependent protein degradation modules in Arabidopsis. Mol Plant 5:573-82
Nusinow, Dmitri A; Helfer, Anne; Hamilton, Elizabeth E et al. (2011) The ELF4-ELF3-LUX complex links the circadian clock to diurnal control of hypocotyl growth. Nature 475:398-402
Baudry, Antoine; Ito, Shogo; Song, Young Hun et al. (2010) F-box proteins FKF1 and LKP2 act in concert with ZEITLUPE to control Arabidopsis clock progression. Plant Cell 22:606-22
Imaizumi, Takato (2010) Arabidopsis circadian clock and photoperiodism: time to think about location. Curr Opin Plant Biol 13:83-9
Song, Young Hun; Ito, Shogo; Imaizumi, Takato (2010) Similarities in the circadian clock and photoperiodism in plants. Curr Opin Plant Biol 13:594-603

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