Systems biology approach identifies nutrient regulation of biological clock in plants

The study will appear in the latest issue of the Proceedings of the National Academy of Sciences. This hypothesis derived from multi-network analysis of Arabidopsis genomic data, and validated experimentally, has shed light on how nutrients affect the molecular networks controlling plant growth and development in response to nutrient sensing.

The study was conducted by a team of researchers at New York University’s Center for Genomics and Systems Biology, Chile’s Pontificia Universidad Católica de Chile, Dartmouth College, and Cold Spring Harbor Labs. The study’s lead authors are Rodrigo A. Gutiérrez of the Pontificia Universidad Católica de Chile and Gloria Coruzzi of NYU’s Center for Genomics and Systems Biology. They note that the systems biology approach to uncovering nutrient regulated gene networks provides new targets for engineering traits in plants of agronomic interest such as increased nitrogen use efficiency, which could lead to reduced fertilizer cost and lowering ground water contamination by nitrates.

Scientists have previously studied how nitrogen nutrients affect gene expression as a way to understand the mechanisms that control plant growth and development. Nitrogen is an essential nutrient and a metabolic signal that is sensed and converted, resulting in the control of gene expression in plants. In addition, nitrate has been shown to serve as a signal for the control of gene expression in Arabidopsis, the first flowering plant to have its entire genome sequenced. There is existing evidence, on a gene-by-gene basis, that products of nitrogen assimilation, the amino acids glutamate (Glu) or glutamine (Gln), might serve as signals of organic nitrogen status that are sensed and in turn regulate gene expression.

To identify genome-wide responses to such organic nitrogen signals, the researchers treated Arabidopsis seedlings with inorganic nitrogen (N) in both the presence and the absence of chemicals that inhibit the assimilation into organic N and conducted a genome-wide analysis of all genes whose expression responds to inorganic or organic forms of nitrogen. Using an integrated network model of molecular interactions for Arabidopsis–constructed by the researchers–in which approximately 7,000 genes are connected by 230,000 molecular interactions, they uncovered a sub-network of genes regulated by organic nitrogen that includes a highly connected network “hub” CCA1, which controls a plant’s biological clock, and target genes involved in nitrogen assimilation.

The findings thus provide evidence that plant nutrition, like animal nutrition, is tightly linked to circadian, or biological clock, functions as scientists have previously hypothesized. Other researchers have recently found that the central clock gene Per2 is necessary for food anticipation in mice. This study indicates that nitrogen nutrition affects CCA1, the central clock gene of plants, suggesting nutritional regulation of the biological clock occurs in plants.