User:Asoph/Stacey Harmer

Stacey Harmer is a chronobiologist whose work centers on the study of circadian rhythms in plants, specifically in Arabidopsis Thaliana and Helianthus. Her research focuses on the molecular nature of the plant circadian clock and its influences on plant physiology. Harmer is currently a professor of Plant Biology in the Department of Plant Biology at the University of California, Davis.

Education
Stacey Harmer achieved her bachelor’s degree in Biochemistry from the University of California, Berkeley, then earned a PhD at the University of California, San Francisco in 1998. At UC San Francisco, she was a Howard Hughes Predoctoral Fellow in Dr. Tony DeFranco’s lab, while researching the systems involving signal transduction by the B-cell antigen receptor.

From 1998 to 2002, Harmer’s post-doctoral studies changed from immunology to plant biology to research under Dr. Steve Kay at the Scripps Research Institute. Harmer received the NIH National Research Service Award and has great skill for exploring and analyzing the circadian rhythms in the lab with her in-depth knowledge in biochemistry and plant anatomy. When Harmer created her own lab, she started to investigate circadian rhythms in plants and the plant clock’s function in plant physiology, which continues to be her primary scientific interest in life.

Sunflower heliotropism
Stacey Harmer also discovered that the circadian clock controls Arabidopsis seedlings’ sensitivity, which was influenced by auxin; sensitive reaction to auxin was different depending on the time of day. Building off this work, Harmer wondered about the significance of circadian clock and auxin signaling network on plant growth, so she studied circadian clock in sunflower heliotropism, or solar tracking. Sunflower’s long stem made it easy to identify its heliotropism. Following the sun’s location, the sunflower’s leaves and stems moved from east to west during light. Anticipating sunrise, the flowers moved from west to east during dark, thus the plant clock played a role in heliotropism.

Since the sunflowers did not have pulvini, organs that controlled solar tracking for other plants, Harmer hypothesized that stem growth may cause heliotropism. She monitored growth of stems and solar tracking in dwarf2 (dw2) sunflowers, which lack gibberellin growth hormones. Due to this deficiency, dw2 sunflowers have short stems and no heliotropism. After treating these flowers with gibberellin hormones, heliotropism was restored. As a result, this day and night movement was caused by the stem’s elongation.

Harmer further hypothesized that heliotropism is irregular growth rates on the opposite sides of the stem. On the east side, the stem had large growth during the day and small growth during the night, but on the west side, the stem experienced the opposite. This contrast indicated that the east side of the stem lengthened during day and the west side lengthened during night, which enabled it to move east to west during day and west to east at night. This uneven growth was controlled by genes influenced by light and circadian rhythm. Despite these findings, there is still an investigation on understanding the molecular mechanism behind the sunflower’s growth rates. Current reports suggest that certain pathways control the stem’s movements during day and night.

Harmer Lab
The Harmer Lab is a research group dedicated to studying the plant circadian clock, in particular the molecular processes and physiology underlying plant development and responses to environmental stimuli such as light and temperature. The Harmer Lab was established in 2001 when Dr. Harmer was recruited to the Department of Plant Biology at the University of California, Davis.

By using Arabidopsis thaliana and the sunflower as models, the Harmer lab focuses on understanding how molecular mechanisms in plant circadian systems control responses to a variety of environmental cues through signaling pathways and physiological timing. Some of the lab's current research projects include investigating processes by which plants respond to fluctuations in light, identifying genes and pathways involved in regulating the plant circadian clock, and analyzing the role of microRNAs in plant gene expression.

Over time, the Harmer Lab has made several important contributions to the field of plant chronobiology:

Identifying several crucial genes involved in plant circadian growth including LHY and CCA1. Discovering DET1, a protein that plays a key role in plant responses to light. Exploring microRNAs involved in overseeing plant development, including the miR156 family.

The Harmer Lab also collaborates with a number of outside research groups: The laboratory of Dr. Xuemei Chen at the University of California, Riverside on microRNA regulation in plants. The laboratory of Dr. Joanne Chory at the Salk Institute for Biological Studies for light signaling in plants. The laboratory of Dr. Steve Kay at the University of Southern California on the plant circadian clock.

References

Harmer lab. Harmer Lab. (n.d.). Retrieved April 6, 2023, from http://harmerlab.plantclock.org/ Harmer, S. L. (2009). The circadian system in higher plants. Annual Review of Plant Biology, 60, 357-377. Harmer, S. L., et al. (2000). Det1, a negative regulator of light-mediated development and gene expression in Arabidopsis, encodes a novel nuclear-localized protein. Cell, 90(4), 683-692. Jung, J. H., et al. (2015). The GIGANTEA-Regulated MicroRNA172 mediates photoperiodic flowering independent of CONSTANS in Arabidopsis. The Plant Cell, 27(8), 1916-1928.