Functions of HKT transporters in sodium transport in roots and in protecting leaves from salinity stress
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Excessive sodium (Na<sup>+</sup>) accumulation in plants due to soil salinity is toxic to most higher plants including crop plants. Many genes encoding Na<sup>+</sup> permeable transporters/channels have been identified for the last 15 years, based on genetic approaches, genome-sequencing projects and functional complementation screening using yeast mutants. The HKT-type transporter/channel class is one of the best characterized Na<sup>+</sup> permeable membrane proteins in plants. Interestingly, most Na<sup>+</sup> permeable proteins including HKT-type transporters/channels in plants were shown or deduced to play a protective role against salinity stress. A Na<sup>+</sup> selective transporter/channel in rice (<i>Oryza sativa</i>), OsHKT2;1, however, has recently been proven to function in "nutritional Na<sup>+</sup> absorption" in K<sup>+</sup>-starved roots rather than functioning in a protective role under salinity stress. Here we review findings on the HKT-type transporters/channels, mainly focusing on the function of OsHKT2;1 that is tightly regulated by K<sup>+</sup>/Na<sup>+</sup> homeostatic mechanisms of rice plants. We also discuss functions of <i>Arabidopsis thaliana</i> AtHKT1;1 and rice OsHKT1;5 in protecting plant leaves from over-accumulating toxic Na<sup>+</sup> concentrations during salinity stress by removing Na<sup>+</sup> from the xylem sap.
- Plant tissue culture letters
Plant tissue culture letters 25(3), 233-239, 2008-06-01
Japanese Society for Plant Cell and Molecular Biology