Structure and transport mechanism of a high-affinity potassium uptake transporter from higher plants

Abstract

POTASSIUM is the most abundant cation in higher plants and is crucial for plant nutrition, growth, tropisms, enzyme homeostasis and osmoregulation^1–4. K⁺ accumulation can be rate-limiting for agricultural production^2–4. K⁺ uptake from soils into roots is largely mediated by high-affinity K⁺ uptake (K_m≈10–40 μM) (refs 1, 2, 5–7). But although K⁺channels allow low-affinity K⁺ uptake^8–10, both the transport mechanism and structure of the high-affinity K⁺ nutrition pathway remain unknown. Here we use expression cloning to isolate a complementary DNA encoding a membrane protein (HKT1) from wheat roots which confers the ability to take up K⁺. The substrate affinity, saturation and cation selectivity of HKT1 correspond to hallmark properties of classical high-affinity K⁺ uptake in plants^1,2,11. The transport mechanism of HKT1 uses K⁺-H⁺ co-uptake. Expression of HKT1 is localized to specific root and leaf regions which represent primary sites for K⁺ uptake in plants^2,3. HKT1 is important for plant nutrition and could possibly contribute to environmental alkali metal toxicities^11–13.