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

Abstract

Summary 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 knockout 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 Ca2+, Mg2+, Na+, NO3−, 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.