Signal interactions in the regulation of root nitrate uptake.

In most aerobic soils, nitrate (NO3(-)) is the main nitrogen source for plants and is often limiting for plant growth and development. To adapt to a changing environment, plants have developed complex regulatory mechanisms that involve short and long-range signalling pathways in response to both NO3(-) availability in the soil and other physiological processes like growth or nitrogen (N) and carbon (C) metabolisms. Over the past decade, transcriptomic approaches largely contributed to the identification of molecular elements involved in these regulatory mechanisms, especially at the level of root NO3(-)uptake. Most strikingly, the data obtained revealed the high level of interaction between N and both hormone and C signalling pathways, suggesting a strong dependence on growth, development, and C metabolism to adapt root NO3(-) uptake to both external NO3(-) availability and the N status of the plant. However, the signalling mechanisms involved in the cross-talk between N, C, and hormones for the regulation of root NO3(-) uptake remain largely obscure. The aim of this review is to discuss the recent advances concerning the regulatory pathways controlling NO3(-) uptake in response to N signalling, hormones, and C in the model plant Arabidopsis thaliana. Then, to further characterize the level of interaction between these signalling pathways we built on publicly available transcriptome data to determine how hormones and C treatments modify the gene network connecting root NO3(-) transporters and their regulators.