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Research reveals nitrogen’s role in Circadian cycle

A group of researchers, which includes faculty from Dartmouth, has determined that organic nitrogen controls a genetic network in plants that regulates both the plant’s nitrogen metabolism and its circadian clock.

C. Robertson McClung (Photo by Joseph Mehling ´69)

The study was conducted by researchers at Dartmouth, New York University’s Center for Genomics and Systems Biology, Chile’s Papal Catholic University, and Cold Spring Harbor Laboratory. The study, titled, “Systems approach identifies an organic nitrogen-responsive gene network that is regulated by the master clock control gene CCA1,” was published in the March 25 issue of the Proceedings of the National Academies of Science.

The circadian clock controls the plant’s response to the time of day, available sunlight, and seasons. Understanding the clock’s underlying genetic mechanisms contributes to efforts to help improve plant productivity and can possibly lead to growing crops that are more resistant to stressful soil or climate conditions.

“Nitrogen is a key component of proteins and other cellular matter, and insufficient nitrogen frequently limits plant growth,” says C. Robertson McClung, professor of biological sciences and an author on the paper. “Our study provides evidence that a plant’s nitrogen nutrition, in other words how much nitrogen is in the plant, and circadian clock function are intimately linked and mutually regulate each other.”

Plants get their nitrogen from the soil, where it is usually found in inorganic form as nitrate. As plants take up the nitrate, it is combined with the products of photosynthesis to make amino acids such as glutamate and glutamine  that, in turn, are primary indicators of the abundance of nitrogen in the plant.

The circadian clock controls a plant's response to the time of day, sunlight, and seasons. (Photo: iStockphoto.com)

The research team studied the effects of glutamate and glutamine on the master clock control gene called CCA1. This study indicates that, in plants, anticipating daytime and photosynthesis, which enables the assimilation of inorganic nitrogen into amino acids, may represent one of the important functions of the clock.

“To our knowledge, this is the first manuscript that uses a systems approach to identify organic nitrogen-responsive gene networks in plants,” says lead author Rodrigo Gutiérrez, a faculty member both at New York University and at Papal Catholic University. “The systems biology approach provides an emerging view of the circadian clock as an integrator of metabolism, physiology, and gene function over time.”

In addition to Gutiérrez and McClung, Xiaodong Xu, a postdoctoral fellow at Dartmouth, was also an author on the paper. Other authors include: Gloria Coruzzi (the senior author on the study), Trevor Stokes, Karen Thum, Mariana Obertello, Manpreet Katari, Alexis Dean, and Damion Nero with New York University; and Milo Tanurdzic with Cold Spring Harbor Lab in New York.

This work was funded by grants to Coruzzi from the National Institutes of Health, the Department of Energy, and the National Science Foundation, and a grant from the National Science Foundation to McClung.

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