Fig. 6

Schematic model of AtNRT2.4 involvement in the regulation of root development by sensing the local and systemic nitrate signaling. AtNRT2.4 perceives local N-deficiency signal and activates the AtANR1 and AtTCP20 mediated signaling pathways, thereby promoting LR elongation and proliferation (left). Conversely, when external nitrate is abundant, it inhibits root elongation by suppressing this cascade (right). Additionally, AtNRT2.4 can sense low nitrate signals to activate the pathway of AtPAP2/AtTT8 regulating the AtF3H-AtDFR/AtANS genes, leading to anthocyanin accumulation (left). AtNRT2.4 also involved the phosphorylation of AtNRT1.1 by the AtCBL1/9-AtCIPK23 complex in response to external nitrate concentration, facilitating the switch between high and low-affinity nitrate transport. Furthermore, systemic N-sufficiency signals inhibit the AtTCP20 and AtANR1-mediated signaling pathways in an AtNRT2.4-dependent manner, thereby suppressing the elongation of the primary root and proliferation of LR on the -N side. In contrast, the systemic N-deficiency signals enable AtNRT2.4 to promote AtANR1, enhancing the elongation of the primary root and proliferation of lateral roots on the + NO₃⁻ side (middle). Gradient-colored dots represent nitrate; arrows indicate positive regulation, and flat ends indicate negative regulation. Blue and red dashed lines represent systemic nitrate sufficiency and deficiency signaling, respectively