Plant HKT Channels: An Updated View on Structure, Function and Gene Regulation

Abstract

HKT channels are a plant protein family involved in sodium (Na+) and potassium (K+) uptake and Na+-K+ homeostasis. Some HKTs underlie salt tolerance responses in plants, while others provide a mechanism to cope with short-term K+ shortage by allowing increased Na+ uptake under K+ starvation conditions. HKT channels present a functionally versatile family divided into two classes, mainly based on a sequence polymorphism found in the sequences underlying the selectivity filter of the first pore loop. Physiologically, most class I members function as sodium uniporters, and class II members as Na+/K+ symporters. Nevertheless, even within these two classes, there is a high functional diversity that, to date, cannot be explained at the molecular level. The high complexity is also reflected at the regulatory level. HKT expression is modulated at the level of transcription, translation, and functionality of the protein. Here, we summarize and discuss the structure and conservation of the HKT channel family from algae to angiosperms. We also outline the latest findings on gene expression and the regulation of HKT channels.

Genome-Wide Identification and Expression Profiling of Potassium Transport-Related Genes in Vigna radiata under Abiotic Stresses

“…In plants, there are two classes of HKTs (HKT1-like and HKT 2-like). Class I HKTs are Na + uniporters and class II HKTs are Na + and K + symporters [ 14 ]. The KEA proteins are closely related to bacterial KefC K + /H + antiporters [ 15 , 16 ].…”

Transcriptome-Wide Analysis Revealed the Potential of the High-Affinity Potassium Transporter (HKT) Gene Family in Rice Salinity Tolerance via Ion Homeostasis

“…Similarly, we also noted that a maximum number of HKT proteins that consisted of five or less motifs were found in subfamily V. The results further noted that the physicochemical properties of all HKT proteins were similar in each subfamily. These results suggest that HKT proteins shared a close evolutionary relationship during biological evolution in plants [ 45 , 46 ]. The intron–exon distribution revealed that most HKT genes possessed two exons and one intron ( Figure 2 ), further confirming that the HKT genes may have close evolutionary relationships in plants [ 47 ].…”

Gene Mapping, Cloning and Association Analysis for Salt Tolerance in Rice

“…This transporter could transport Na + out of the xylem, and transport Na + from the phloem back to the root where it was excreted from the plant through the action of other Na + transporters. This process reduced the Na + content in the shoot, regulated the Na + /K + balance in the shoots, and improved rice salt tolerance [ 68 ].…”