Signals and players in the transcriptional regulation of root responses by local and systemic N signaling in Arabidopsis thaliana.

In natural environments, nitrogen (N) concentration in the soil fluctuates greatly and is often limiting for plant growth and development. The ability of plants to respond to changes in N availability is therefore essential for adaptation. The response of plants to N variations consists in particular of adjusting root N uptake systems and root architecture. To do so, plants integrate local sensing and signaling of external N availability with systemic sensing and signaling of their internal N status, in order to tune the functional and structural properties of the root system in accordance with the N demand for growth of the whole plant. Transcriptional regulation of gene expression is one of the most important processes plants use to adapt the properties of the root system in response to local and long-distance N pathways. This review focuses on the mechanisms that give rise to transcriptional responses in Arabidopsis roots under N fluctuations, with an emphasis on those associated with the regulation of nitrate uptake and transport systems. We discuss the putative long-distance signals triggering the gene expression responses, as well as the molecular players that locally induce transcriptional changes. We also highlight several observations revealing the importance of adopting an integrative approach in the regulation of N signaling.