Plant HKT Channels: an updated view on structure, function and gene regulation

Authors: RIEDELSBERGER, JANIN - University Of Talca; MILLER, JULIA - Cornell University; VALDEBENITO-MATURANA, BRAULIO - University Of Talca; Pineros, Miguel; GONZALES, WENDY - University Of Talca; DREYER, INGO - University Of Talca

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2021
Publication Date: 2/14/2021
Citation: Riedelsberger, J., Miller, J.K., Valdebenito-Maturana, B., Pineros, M., Gonzales, W., Dreyer, I. 2021. Plant HKT Channels: an updated view on structure, function and gene regulation. International Journal of Molecular Sciences. 22(4):1892. https://doi.org/10.3390/ijms22041892.
DOI: https://doi.org/10.3390/ijms22041892

Interpretive Summary: In plants, potassium (K) is an essential mineral nutrient, which plays a vital role as an osmolyte, maintaining the cell's turgor. The uptake of K+ from the soil by the roots and its redistribution and accumulation throughout the plant is mediated by the combined activity of various types of K+ transport proteins. Among these, members of the HKT family can also transport other cations (such as sodium) in addition to K+. Such a functional hallmark enables these transporters to be involved in cellular processes to fine-tune the Na to K balance, particularly under environmentally unfavorable conditions, such as those experienced during salt stress or K deficiency. Based on their known functions and predicted protein structures, the members of this family of transport proteins can be subdivided into two main classes. This review examines the evolution of the structure of the HKT channel family, as the plants evolved from algae to angiosperms, and describes the latest findings on the processes regulating their expression. The investigation of the structure-function relations of transport proteins provides a mechanistic understanding of how plants efficiently make use of mineral nutrients (K in the present case) to maintain agricultural productivity, even under abiotic stress conditions found in marginal soils.

Technical 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.