Overexpression of PeHKT1;1 Improves Salt Tolerance in Populus

Soil salinization is an increasingly serious threat that limits plant growth and development. Class I transporters of the high-affinity K⁺ transporter (HKT) family have been demonstrated to be involved in salt tolerance by contributing to Na⁺ exclusion from roots and shoots. Here, we isolated the PeHKT1;1 gene from hybrid poplar based on the sequences of the Populus trichocarpa genome. The full-length PeHKT1;1 gene was 2173 bp, including a 1608 bp open reading frame (ORF) encoding 535 amino acids and containing eight distinct transmembrane domains. Multiple sequence alignment and phylogenetic analysis suggested that the PeHKT1;1 protein had a typical S⁻G⁻G⁻G signature for the P-loop domains and belonged to class I of HKT transporters. PeHKT1;1 transcripts were mainly detected in stem and root, and were remarkably induced by salt stress treatment. In further characterization of its functions, overexpression of PeHKT1;1 in Populus davidiana × Populus bolleana resulted in a better relative growth rate in phenotypic analysis, including root and plant height, and exhibited higher catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities than non-transgenic poplar under salt stress conditions. These observations indicated that PeHKT1;1 may enhance salt tolerance by improving the efficiency of antioxidant systems. Together, these data suggest that PeHKT1;1 plays an important role in response to salt stress in Populus.