Abstract
Sodium and potassium are two alkali cations abundant in the biosphere. Potassium is essential for plants and its concentration must be maintained at approximately 150 mM in the plant cell cytoplasm including under circumstances where its concentration is much lower in soil. On the other hand, sodium must be extruded from the plant or accumulated either in the vacuole or in specific plant structures. Maintaining a high intracellular K+/Na+ ratio under adverse environmental conditions or in the presence of salt is essential to maintain cellular homeostasis and to avoid toxicity. The baker’s yeast, Saccharomyces cerevisiae, has been used to identify and characterize participants in potassium and sodium homeostasis in plants for many years. Its utility resides in the fact that the electric gradient across the membrane and the vacuoles is similar to plants. Most plant proteins can be expressed in yeast and are functional in this unicellular model system, which allows for productive structure-function studies for ion transporting proteins. Moreover, yeast can also be used as a high-throughput platform for the identification of genes that confer stress tolerance and for the study of protein–protein interactions. In this review, we summarize advances regarding potassium and sodium transport that have been discovered using the yeast model system, the state-of-the-art of the available techniques and the future directions and opportunities in this field.
Highlights
Potassium (K+) and sodium (Na+) are two nutrients essential for plant life
It has been observed that low K+ concentrations in the soil during a long growth period will produce plants with a higher transpiration rate and increased stomata frequency per leaf area; while, higher internal K+ is correlated with a lower transpiration rate and fewer stomata per leaf area [6]
The first HAKs isolated in plants were obtained from barley root cDNA, using an RT-PCR approach based on amino acid homology between the sequences of two K+ transporters known to belong to the HAK family, Kup of Escherichia coli [89] and HAK1 of Schwanniomyces occidentalis [90]
Summary
Potassium (K+) and sodium (Na+) are two nutrients essential for plant life. They are absorbed from the soil through the roots, translocated to the rest of plant organs through movement into the xylem/phloem, to be compartmentalized in the organs where they exert their specific functions. The first HAKs isolated in plants were obtained from barley root cDNA, using an RT-PCR approach based on amino acid homology between the sequences of two K+ transporters known to belong to the HAK family, Kup of Escherichia coli [89] and HAK1 of Schwanniomyces occidentalis [90] The characterization of these genes (HvHAK1 and HvHAK2) was carried out in trk trk yeast mutants, where the authors concluded that only HvHAK1 was able to rescue the growth phenotype, confirming the high affinity K+ transporter function [91]. In the case of the vacuolar channels, to use the yeast functional complementation approach, plant genes are expressed in yvc mutants and their activity is analyzed in isolated vacuoles.
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