Previously Unknown Regulatory Mechanism for Circadian and Temperature Signaling Pathways Revealed

Ever wondered why people become tired when the sun goes down? What causes some flower petals to open during the day and close at night? Or how monarch butterflies ascertain when to migrate south?

Dmitri Nusinow PhD, and Maria Sorkin, PhD working together with colleagues in the Plant Transformation Facility. Image Credit: Donald Danforth Plant Science Center

Life on Earth has evolved to be able to predict the time. The circadian clock is a mechanism that allows plants and animals to have rhythmic, biological responses to the Earth’s 24-hour and 365-day cycles by utilizing environmental cues such as light and temperature. Dmitri Nusinow, PhD, Associate Member, Danforth Plant Science Center, and former Nusinow Graduate Student Maria Sorkin, PhD, performed a study that discovered a novel protein complex in plants that regulates temperature responsiveness via the circadian clock.

Because climate change affects daily and seasonal temperature patterns, such as warmer nights and winters, it is indeed important to understand how plants interpret and respond to thermal cues. Their findings were recently published in Plant Physiology, a scientific journal.

The clock is essential for plants to correctly respond to temperature stimuli. The circadian clock in Arabidopsis is well-studied, so the most exciting part of this project was finding a brand-new protein complex that regulates temperature responses. No one else had discovered this interaction, even in an established system.”

Maria Sorkin, Graduate Student, Danforth Plant Science Center

Scientists have discovered a number of ways in which the circadian clock aids plants in acclimating to temperature fluctuations and surviving stress, particularly in model species such as Arabidopsis.

The complex is made up of three proteins that interact in the evening to help acclimatize to cooler temperatures. The study team made an important discovery by establishing a mechanistic link between these proteins and the time of day at which they interact.

Sorkin went to heroic lengths to discover how these three protein ‘puzzle pieces’ come together. We are always looking for protein complexes in our work, but we don’t know how they will interact. Maria’s dedication solved that puzzle.”

Dmitri Nusinow, Associate Member, Danforth Plant Science Center

Their advancements are the result of three years of hard work - sometimes late at night and early in the morning—to decipher how and when these proteins interact. Surprisingly, the group “saw new complexes formed when we ran our experiments at different times of the day, even just hours apart from each other,” Nusinow comments.

Partnership with the Danforth Center's Proteomics & Mass Spectrometry Facility (PMSF) and plant growth team was required for the researcher's experiments. The PMSF used cutting-edge technology to identify hundreds of possible proteins for the team to investigate. Furthermore, plant material was generously shared for analysis of these proteins by collaborators from the University of Freiburg in Germany, the Plant-Environment Signaling Group at Utrecht University, and the Fundación Instituto Leloir, Instituto de Investigaciones Bioqumicas de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas in Argentina.

Stefanie King, a Co-Author and second-year Graduate Student at Washington University in St. Louis, is a co-author and second-year graduate student in the Nusinow lab. “I’m grateful to learn from Maria and design experiments to look at the structure and regulation of the complex as a whole,” King says.

Now that scientists have shown that the protein complex interacts at specific times of day, they want to learn more about how it interacts at different temperatures. In addition, Stefanie is looking forward to guiding an NSF REU intern in these techniques over the summer.