The two-pore channel TPK1 gene encodes the vacuolar K + conductance and plays a role in K + homeostasis

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Abstract
The Arabidopsis thaliana genome contains five genes that encode two pore K + (TPK) channels. The most abundantly expressed isoform of this family, TPK1, is expressed at the tonoplast where it mediates K + -selective currents between cytoplasmic and vacuolar compartments. TPK1 open probability depends on both cytoplasmic Ca 2+ and cytoplasmic pH but not on the tonoplast membrane voltage. The channel shows intrinsic rectification and can be blocked by Ba 2+ , tetraethylammonium, and quinine. TPK1 current was found in all shoot cell types and shows all of the hallmarks of the previously described vacuolar K (VK) tonoplast channel characterized in guard cells. Characterization of TPK1 loss-of-function mutants and TPK1-overexpressing plants shows that TPK1 has a role in intracellular K + homeostasis affecting seedling growth at high and low ambient K + levels. In stomata, TPK1 function is consistent with vacuolar K + release, and removal of this channel leads to slower stomatal closure kinetics. During germination, TPK1 contributes to the radicle development through vacuolar K + deposition to provide expansion growth or in the redistribution of essential minerals.