C-terminally encoded peptides act as signals to increase cotton root nitrate uptake under nonuniform salinity

Abstract Soil salinity is often heterogeneous in saline fields. Nonuniform root salinity increases nitrate uptake into cotton (Gossypium hirsutum) root portions exposed to low salinity, which may be regulated by root portions exposed to high salinity through a systemic long-distance signaling mechanism. However, the signals transmitted between shoots and roots and their precise molecular mechanisms for regulating nitrate uptake remain unknown. Here, we showed that nonuniform root salinity treatment using split-root systems increases the expression of C-TERMINALLY ENCODED PEPTIDE (GhCEP) genes in high-saline-treated root portions. GhCEP peptides originating in high-saline-treated root portions act as ascending long-distance mobile signals transported to the shoots to promote the expression of CEP DOWNSTREAM (GhCEPD) genes by inducing the expression of CEP receptor (GhCEPR) genes. The shoot-derived GhCEPD polypeptides act as descending mobile signals transported to the roots through the phloem, increasing the expression of nitrate transport genes NITRATE TRANSPORTER 1.1 (GhNRT1.1), GhNRT2.1, and GhNRT1.5 in nonsaline-treated root portions, thereby increasing nitrate uptake in the nonsaline-treated root portions. This study indicates that GhCEP and GhCEPD signals are transported between roots and shoots to increase nitrate uptake in cotton, and the transport from the nonsaline root side is in response to nonuniform root salinity distribution.