Inhibition of SlSKOR by SlCIPK23-SlCBL1/9 uncovers CIPK-CBL-target network rewiring in land plants.

Transport of K + to the xylem is a key process in the mineral nutrition of the shoots. Although CIPK-CBL complexes have been widely shown to regulate K + uptake transport systems, no information is available about the xylem ones. Here, we studied the physiological roles of the voltage-gated K + channel SlSKOR and its regulation by the SlCIPK23-SlCBL1/9 complexes in tomato plants. We phenotyped gene-edited slskor and slcipk23 tomato knock-out mutants and carried out two-electrode voltage-clamp (TEVC) and BiFC assays in Xenopus oocytes as key approaches. SlSKOR was preferentially expressed in the root stele and was important not only for K + transport to shoots but also, indirectly, for that of Ca 2+ , Mg 2+ , Na + , NO 3 - and Cl - . Surprisingly, the SlCIPK23-SlCBL1/9 complexes turned out to be negative regulators of SlSKOR. Inhibition of SlSKOR by SlCIPK23-SlCBL1/9 was observed in Xenopus oocytes and tomato plants. Regulation of SKOR-like channels by CIPK23-CBL1 complexes was also present in Medicago, grapevine and lettuce but not in Arabidopsis and saltwater cress. Our results provide a molecular framework for coordinating root K + uptake and its translocation to the shoot by SlCIPK23-SlCBL1/9 in tomato plants. Moreover, they evidenced that CIPK-CBL-target networks have evolved differently in land plants.