Constitutive expression of CmSKOR, an outward K+ channel gene from melon, in Arabidopsis thaliana involved in saline tolerance

Shaker-like K⁺ outward rectifying channel (SKOR) is involved in mediating long-distance K⁺ transport from roots to shoots. In this study, a Shaker-like outward K⁺ channel gene CmSKOR (GenBank accession number MF447462) was isolated from melon (Cucumis melo L.). Phylogenetic analysis showed that CmSKOR belongs to the SKOR-subfamily in the Shaker-like K⁺ channel family. Electrophysiological experiments indicated that CmSKOR was a K⁺-permeable channel with low affinity. Expressed in Xenopus oocytes, CmSKOR displayed classical Shaker-like outwardly rectifying K⁺ currents. Confocal imaging of a CmSKOR - yellow fluorescent fusion protein (YFP) in transgenic Nicotiana tabacum leaves indicated that CmSKOR was located in the plasma membrane. Transcript analysis showed CmSKOR predominantly expressed in melon roots and with lower abundance in stem and leaves. In addition, both external K⁺ and NaCl treatment could up-regulate the expression of CmSKOR in melon and enhance the K⁺ content in shoot. Constitutive overexpressed CmSKOR in Arabidopsis thaliana, the transgenic plants showed changes in root length in MS plates, displayed higher maximum photochemical efficiency of PSII (Fv/Fm), higher fresh and dry weight, and accumulation of K⁺ in shoot, together with the changes of transcript amount of CmSKOR with NaCl treatments in mixture substrate. In conclusion, it was proposed that CmSKOR may play the role on distributing K⁺ to the shoot in melon and its constitutive expression in Arabidopsis improved saline tolerance by maintaining K⁺ homeostasis in the plant.