Shoot-derived polypeptide signals control nitrate acquisition in root in response to fluctuating nitrogen environments

Nitrogen (N), which is mostly present as nitrate in soils, is an essential macronutrient that plays a crucial role in plant development. However, due to the high mobility of nitrate ions through soil with water, marked spatiotemporal fluctuations can occur with respect to soil nitrate availability. To cope with such fluctuations in the external N environment, plants have evolved regulatory mechanisms that enable them to modulate the efficiency of root N acquisition in response to their internal N demand and rhizosphere N availability. This systemic adaptive response to N deficiency is mediated by shoot-to-root mobile polypeptides, CEPD and CEPDL2. CEPD is induced in shoots in response to the peptide hormone CEP, which is a root-derived N deficiency signal, whereas CEPDL2 is induced in response to the shoot's own N deficiency. CEPD/CEPDL2 polypeptides cooperatively regulate nitrate uptake in roots by both transcriptional upregulation of high-affinity nitrate transporter genes, such as NRT2.1, and post-translational activation of NRT2.1 via dephosphorylation by the protein phosphatase CEPH, which is also induced by CEPDs.　 Using an unbiased proteomic approach and ChIP-seq analysis, we further identified that CEPD/CEPDL2 interact with the TGA1/4 transcription factor in roots, functioning as co-activators to enhance the transcription of nitrate uptake genes. Here, we will present our progress in understanding systemic signaling to N deficiency in plants.