Na+-preferential Ion Transporter HKT1;1 Mediates Salt Tolerance in Blueberry

Published:31 Oct.2023 Source:Plant Physiology

Soil salinity is a major environmental factor constraining growth and productivity of highbush blueberry (Vaccinium corymbosum). Leaf Na⁺ content is associated with variation in salt tolerance among blueberry cultivars; however, the determinants and mechanisms conferring leaf Na⁺ exclusion are unknown.

Here, we observed that the blueberry cultivar ‘Duke’ was more tolerant than ‘Sweetheart’ and accumulated less Na⁺ in leaves under salt stress conditions. Through transcript profiling, we identified a member of the high-affinity K⁺ transporter (HKT) family in blueberry, VcHKT1;1, as a candidate gene involved in leaf Na⁺ exclusion and salt tolerance. VcHKT1;1 encodes a Na⁺-preferential transporter localized to the plasma membrane and is preferentially expressed in the root stele. Heterologous expression of VcHKT1;1 in Arabidopsis (Arabidopsis thaliana) rescued the salt hypersensitivity phenotype of the athkt1 mutant. Decreased VcHKT1;1 transcript levels in blueberry plants expressing antisense-VcHKT1;1 led to increased Na⁺ concentrations in xylem sap and higher leaf Na⁺ contents compared with wild-type plants, indicating that VcHKT1;1 promotes leaf Na⁺ exclusion by retrieving Na⁺ from xylem sap.

A naturally occurring 8-bp insertion in the promoter increased the transcription level of VcHKT1;1, thus promoting leaf Na⁺ exclusion and blueberry salt tolerance. Collectively, we provide evidence that VcHKT1;1 promotes leaf Na⁺ exclusion and propose natural variation in VcHKT1;1 will be valuable for breeding Na⁺-tolerant blueberry cultivars in the future.