| Abstract |
Plants uptake nitrogen (N) from the soil mainly in the form of nitrate. However, nitrate is often distributed heterogeneously in natural soil. Plants, therefore, have a systemic long-distance signalling mechanism by which N starvation on one side of the root leads to a compensatory N uptake on the other N-rich side1,2. This systemic N acquisition response is triggered by a root-to-shoot mobile peptide hormone, C-TERMINALLY ENCODED PEPTIDE (CEP), originating from the N-starved roots3,4, but the molecular nature of the descending shoot-to-root signal remains elusive. Here, we show that phloem-specific polypeptides that are induced in leaves upon perception of root-derived CEP act as descending long-distance mobile signals translocated to each root. These shoot-derived polypeptides, which we named CEP DOWNSTREAM 1 (CEPD1) and CEPD2, upregulate the expression of the nitrate transporter gene NRT2.1 in roots specifically when nitrate is present in the rhizosphere. Arabidopsis plants deficient in this pathway show impaired systemic N acquisition response accompanied with N-deficiency symptoms. These fundamental mechanistic insights should provide a conceptual framework for understanding systemic nutrient acquisition responses in plants.
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