ZxSKOR is important for salinity and drought tolerance of Zygophyllum xanthoxylum by maintaining K+ homeostasis

Abstract

As an important nutrient element, K+ plays a crucial role in plant stress resistance. It was reported that the stelar K+ outward rectifying channel (SKOR) is involved in loading K+ into xylem for its transport from roots to shoots. Zygophyllum xanthoxylum, a succulent woody xerophyte, could maintain stable K+ concentration in leaves to adapt to salt and arid environments. Here we characterized ZxSKOR from Z. xanthoxylum, ZxSKOR expression patterns and Na+ and K+ accumulation in Z. xanthoxylum treated with various concentrations of KCl and NaCl and −0.5 MPa osmotic stress were investigated in order to assess the contribution of ZxSKOR to K+ homeostasis. The results showed that ZxSKOR was predominantly expressed in roots and stems rather than in leaves. Its expression levels in roots and stems increased significantly accompanied by an increase in K+ concentration in leaves when plants were exposed to 5–10 mM KCl. Moreover, a positive correlation was identified not only between ZxSKOR expression in roots and K+ accumulation in shoots, but also between ZxSKOR expression in stems and K+ accumulation in leaves. Transcription levels of ZxSKOR in roots and stems under high salinity (100–150 mM NaCl) and osmotic stress (−0.5 MPa) were 2.0–2.8 times those in plants grown in the absence of NaCl or osmotic stress. Concomitantly, the expression level of ZxSKOR in roots under osmotic stress plus salt (−0.5 MPa +50 mM NaCl) was significantly higher than that under osmotic stress (−0.5 MPa) alone during 12–48 h of treatment. We propose that ZxSKOR in roots and stems is well-coordinated to mediate long-distance K+ transport and perhaps plays an important role in K+ accumulation and homeostasis in Z. xanthoxylum under salt as well as drought stress.