Changes in Expression Level of OsHKT1;5 Alters Activity of Membrane Transporters Involved in K+ and Ca2+ Acquisition and Homeostasis in Salinized Rice Roots

Abstract

<jats:p>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.</jats:p>

Identification and Characterization of Long Non-coding RNA in Tomato Roots Under Salt Stress

“…In Solanum cheesmaniae , gene silencing of ScHKT1;2 could result in an increasing Na + /K + ratio and a salt-sensitive phenotype, while the function loss of ScHKT1;1 in rootstock could significantly reduce the ratio of Na + /K + in leaf and flower tissues ( Ra et al, 2021 ). Besides, OsHKT1;5 is also a key determinant of salt tolerance in rice ( Nayef et al, 2020 ).…”

Comparative Analysis of Root Na+ Relation under Salinity between Oryza sativa and Oryza coarctata

“…This pattern of Na + transport is effective to avoid shoot Na + toxicity. Although a functional role of OsHKT1;5 is still questioned due to direct measurements of Na + flux from root stele [ 58 ], OsHKT1;5 within the SKC1 locus is suggested to mediate xylem Na + unloading that reduces shoot Na + accumulation under salinity [ 59 ]. In addition, effective Na + sequestration into root vacuoles through NHX was found to be a key determinant of salinity tolerance in barley and wheat [ 21 , 60 ].…”

To exclude or to accumulate? Revealing the role of the sodium HKT1;5 transporter in plant adaptive responses to varying soil salinity

“…Salinized roots of rice sos1 mutants show reduced OsHKT1;5 expression, presumably to protect roots from accumulating lethal levels of Na + (due to loss of SOS1 function and recirculation of Na + from xylem to root by HKT1;5; El Mahi et al, 2019). Data from recent electrophysiological studies also show that OsHKT1;5 (SKC1) NIL lines (showing higher OsHKT1;5 expression) do not show Na + reabsorption by root xylem parenchyma compared to the wild type parent (Al Nayef et al, 2020). Instead, changes in the expression level of OsHKT1;5 correlates with alterations in expression of membrane transporters (including SOS1).…”