Nutrient dose-responsive transcriptome changes driven by Michaelis-Menten kinetics underlie plant growth rates

Rapid transcriptional responses allow plants to adapt to environmental change. While changes in transcription patterns are routinely documented, rates of change in transcriptomic responses to environmental cues receives less attention. To address this knowledge gap, we profiled Arabidopsis thaliana root transcriptomic responses to a series of treatment conditions that varied the key plant nutrient – Nitrogen (N) - over time. Through fitting Michaelis-Menten models to gene expression patterns, we found that N increases rates of transcription through the TGA1 transcription factor. We employed a cell-based system to capture TGA1-dependent gene regulation events, and found TGA1 is a transcriptional activator, regulating N-uptake and N-metabolism genes upon changes in N. Using transgenic TGA1 overexpression lines we found TGA1 dramatically enhances growth rates. Collectively, our results demonstrate that TGA1 significantly improves plant growth rates by regulating rate of transcription of genes involved in key steps of N metabolism.