HKT K⁺ transporters mediate K⁺ uptake and contribute to K⁺ homeostasis in rice under salt stress

Abstract

Excessive accumulation of Na⁺ in plants disturbs cellular functions and inhibits K⁺ uptake under salt stress condition. It is supposed that Na⁺ and K⁺ homeostasis is crucial for plant salt tolerance. HKT-type transporters mediate uptake of K⁺ and Na⁺, and play important roles in salt tolerance by removing Na⁺ from xylem sap and maintaining K⁺/Na⁺ homeostasis. Previous functional characterization of rice HKT transporter in yeast expression system have shown that OsHKT2;2 which was isolated from salt-tolerant cultivar (cv Pokkali) functions as a Na⁺/K⁺ co-transporter and a single amino acid mutant of Na⁺ transporter OsHKT2;1 (OsHKT2;1S88G) mediates high affinity-K⁺ transport in yeast.
In this study, we carried out a functional analysis of these HKT transporters using transgenic rice plants. When overexpressed in rice, OsHKT2;1S88G increased K⁺ content in leaves under low K⁺ and high Na⁺ condition. Also overexpression of OsHKT2;1S88G and OsHKT2;2 resulted in higher K⁺/Na⁺ ratio compared with control. Our results suggest that these transporters mediate K⁺ uptake and contribute to K⁺/Na⁺ homeostasis under salt stress condition.