| Summary: | Root system architecture (RSA) is required for the acquisition of water and mineral nutrients from the soil. One of the essential nutrients, nitrate (NO<sub>3</sub><sup>−</sup>), is sensed and transported by nitrate transporters <i>NRT1.1</i> and <i>NRT2.1</i> in the plants. Nitrate transporter 1.1 (<i>NRT1.1</i>) is a dual-affinity nitrate transporter phosphorylated at the T101 residue by calcineurin B-like interacting protein kinase (CIPKs); it also regulates the expression of other key nitrate assimilatory genes. The differential phosphorylation (phosphorylation and dephosphorylation) strategies and underlying Ca<sup>2+</sup> signaling mechanism of <i>NRT1.1</i> stimulate lateral root growth by activating the auxin transport activity and Ca<sup>2+</sup>-ANR1 signaling at the plasma membrane and the endosomes, respectively. NO<sub>3</sub><sup>−</sup> additionally functions as a signal molecule that forms a signaling system, which consists of a vast array of transcription factors that control root system architecture that either stimulate or inhibit lateral and primary root development in response to localized and high nitrate (NO<sub>3</sub><sup>−</sup>), respectively. This review elucidates the so-far identified nitrate transporters, nitrate sensing, signal transduction, and the key roles of nitrate transporters and its downstream transcriptional regulatory network in the primary and lateral root development in <i>Arabidopsis thaliana</i> under stress conditions.
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