Graduate Student Washington University in St. Louis
The daily rise and fall of the sun is one of the most dependable environmental patterns that an organism experiences. As such, organisms from all kingdoms of life have evolved an endogenous biological timekeeper called the circadian clock that anticipates and responds to these daily and seasonal patterns. In plants, daylength strongly entrains, or synchronizes, the clock to a 24-hour period to coordinate phenotypes like temperature response, flowering time, and vegetative growth with the appropriate time of day or year. To understand how the clock is connected to environmental input and circadian response output pathways, we used affinity purification coupled with mass spectrometry (APMS) to identify novel protein-protein interactions of the core circadian oscillator proteins. We have completed APMS for 14 of the core circadian clock proteins, producing a near-comprehensive protein-protein interactome for the circadian clock. By defining a circadian clock interactome, we have discovered new connections between the clock and input/output pathways. For instance, based on the identification of novel protein-protein interactions between the core clock transcriptional co-regulators NIGHT LIGHT AND CLOCK REGULATED 1 and 2 (LNK1/LNK2) and several cold-responsive proteins, we hypothesized that the LNKs may play a role in coordinating the response to cold temperature. We found that synchronization of the clock to temperature cycles is delayed in when LNK1 and/or LNK2 are lost, indicating that the LNKs are necessary for temperature entrainment of the clock. It is not well understood how the clock perceives and responds to temperature—especially cold temperatures. This connection between core circadian clock proteins and cold responsive elements could provide insight into how the clock is entrained by temperature and how it helps the plant cope with cold stress.
Coauthors: Dmitri Nusinow, Dr. – Danforth Plant Science Center