Highly selective inward-rectifying potassium channel that mediate potassium uptake by plant roots in response to low K(+) conditions, by a calcium-, CBL-, and CIPK-dependent pathway. Positively regulated by phosphorylation by CIPK23. Negatively regulated by a kinase-independent regulatory mechanism involving a competing direct binding of CBL10. Involved in the stomatal regulation by monitoring the turgor pressure in guard cells. Assuming opened or closed conformations in response to the voltage difference across the membrane, the channel is activated by hyperpolarization. May interact with the cytoskeleton or with regulatory proteins (PubMed:12678562, PubMed:16814720, PubMed:16895985, PubMed:17898163, PubMed:9572739). Is essential with POT5/HAK5 for high-affinity potassium uptake in roots during seedling establishment and postgermination growth under low potassium conditions (PubMed:20413648). The potassium channel is probably composed of a homo- or heterotetrameric complex of pore-forming subunits. Possible heteromultimer with AKT2 or KAT3. Part of a K(+)-channel calcium-sensing kinase/phosphatase complex composed by a calcium sensor CBL (CBL1, CBL2, CBL3 or CBL9), a kinase CIPK (CIPK6, CIPK16 or CIPK23), a phosphatase PP2C (AIP1) and a K(+)-channel (AKT1). Interacts directly with AIP1, CBL10, CIPK6, CIPK16 and CIPK23. Preferentially expressed in the peripheral cell layers of root mature including root cortex and root hairs. Detected also, at a lower level, in the mesophyll of the leaves and at restricted sites corresponding to hydathodes and guard cells. In roots, strongly reduced after 2,4-dichlorophenoxyacetic acid (2,4-D) treatment and weakly reduced after benzyladenine (BA) treatment. In shoots, strongly reduced after abscisic acid (ABA) treatment and induced after benzyladenine (BA) treatment. The segment S4 is probably the voltage-sensor and is characterized by a series of positively charged amino acids. The pore-forming region H5 is enclosed by the transmembrane segments S5 and S6 in the Shaker-type (1P/6TM) and contains the GYGD signature motif which seems to be involved in potassium selectivity. The KHA domain (rich in hydrophobic and acidic residues) present in the C-terminal part is likely to be important for tetramerization. Phosphorylated by CIPK proteins CIPK6, CIPK16 and CIPK23. The activation by phosphorylation is induced by low K(+) conditions and stimulates K(+) uptake and relocation. Dephosphorylation by AIP1 repressed the transport activity. Belongs to the potassium channel family. Plant (TC 1.A.1.4) subfamily.