Changes in Expression Level of OsHKT1;5 Alters Activity of Membrane Transporters Involved in K+ and Ca2+ Acquisition and Homeostasis in Salinized Rice Roots
Mohammad Alnayef, Celymar Solis, Lana Shabala, Takaaki Ogura, Zhong‐Hua Chen, Jayakumar Bose, Frans J. M. Maathuis, Gayatri Venkataraman, Keitaro Tanoi, Min Yu, Meixue Zhou, Tomoaki Horie, Sergey Shabala
Abstract
In rice, the OsHKT1;5 gene has been reported to be a critical determinant of salt tolerance. This gene is harbored by the SKC1 locus, and its role was attributed to Na+ unloading from the xylem. No direct evidence, however, was provided in previous studies. Also, the reported function of SKC1 on the loading and delivery of K+ to the shoot remains to be explained. In this work, we used an electrophysiological approach to compare the kinetics of Na+ uptake by root xylem parenchyma cells using wild type (WT) and NIL(SKC1) plants. Our data showed that Na+ reabsorption was observed in WT, but not NIL(SKC1) plants, thus questioning the functional role of HKT1;5 as a transporter operating in the direct Na+ removal from the xylem. Instead, changes in the expression level of HKT1;5 altered the activity of membrane transporters involved in K+ and Ca2+ acquisition and homeostasis in the rice epidermis and stele, explaining the observed phenotype. We conclude that the role of HKT1;5 in plant salinity tolerance cannot be attributed to merely reducing Na+ concentration in the xylem sap but triggers a complex feedback regulation of activities of other transporters involved in the maintenance of plant ionic homeostasis and signaling under stress conditions.