TY - JOUR A1 - Rocchetti, Alessandra A1 - Sharma, Tripti A1 - Wulfetange, Camilla A1 - Scholz-Starke, Joachim A1 - Grippa, Alexandra A1 - Carpaneto, Armando A1 - Dreyer, Ingo A1 - Vitale, Alessandro A1 - Czempinski, Katrin A1 - Pedrazzini, Emanuela T1 - The putative K+ channel subunit AtKCO3 forms stable dimers in arabidopsis JF - Frontiers in plant science N2 - The permeation pore of K+ channels is formed by four copies of the pore domain. AtKCO3 is the only putative voltage-independent K+ channel subunit of Arabidopsis thaliana with a single pore domain. KCO3-like proteins recently emerged in evolution and, to date, have been found only in the genus Arabidopsis (A. thaliana and A. lyrata). We show that the absence of KCO3 does not cause marked changes in growth under various conditions. Only under osmotic stress we observed reduced root growth of the kco3-1 null-allele line. This phenotype was complemented by expressing a KCO3 mutant with an inactive pore, indicating that the function of KCO3 under osmotic stress does not depend on its direct ability to transport ions. Constitutively overexpressed AtKCO3 or AtKCO3::G FP are efficiently sorted to the tonoplast indicating that the protein is approved by the endoplasmic reticulum quality control. However, vacuoles isolated from transgenic plants do not have significant alterations in current density. Consistently, both AtKCO3 and AtKCO3::GFP are detected as homodimers upon velocity gradient centrifugation, an assembly state that would not allow for activity. We conclude that if AtKCO3 ever functions as a K+ channel, active tetramers are held by particularly weak interactions, are formed only in unknown specific conditions and may require partner proteins. KW - Arabidopsis KW - membrane proteins KW - potassium channels KW - protein assembly KW - tonoplast Y1 - 2012 U6 - https://doi.org/10.3389/fpls.2012.00251 SN - 1664-462X VL - 3 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Lucia Gomez-Porras, Judith A1 - Mauricio Riano-Pachon, Diego A1 - Benito, Begona A1 - Haro, Rosario A1 - Sklodowski, Kamil A1 - Rodriguez-Navarro, Alonso A1 - Dreyer, Ingo T1 - Phylogenetic analysis of K+ transporters in bryophytes, lycophytes, and flowering plants indicates a specialization of vascular plants JF - Frontiers in plant science N2 - As heritage from early evolution, potassium (K+) is absolutely necessary for all living cells. It plays significant roles as stabilizer in metabolism and is important for enzyme activation, stabilization of protein synthesis, and neutralization of negative charges on cellular molecules as proteins and nucleic acids. Land plants even enlarged this spectrum of K+ utilization after having gone ashore, despite the fact that K+ is far less available in their new oligotrophic habitats than in sea water. Inevitably, plant cells had to improve and to develop unique transport systems for K+ accumulation and distribution. In the past two decades a manifold of K+ transporters from flowering plants has been identified at the molecular level. The recently published genome of the fern ally Selaginella moellendorffii now helps in providing a better understanding on the molecular changes involved in the colonization of land and the development of the vasculature and the seeds. In this article we present an inventory of K+ transporters of this lycophyte and pigeonhole them together with their relatives from the moss Physcomitrella patens, the monocotyledon Oryza sativa, and two dicotyledonous species, the herbaceous plant Arabidopsis thaliana, and the tree Populus trichocarpa. Interestingly, the transition of green plants from an aqueous to a dry environment coincides with a dramatic reduction in the diversity of voltage-gated potassium channels followed by a diversification on the basis of one surviving K+ channel class. The first appearance of K+ release (K-out) channels in S. moellendorffii that were shown in Arabidopsis to be involved in xylem loading and guard cell closure coincides with the specialization of vascular plants and may indicate an important adaptive step. KW - potassium KW - transport KW - channel KW - voltage-dependent KW - voltage-independent KW - high-affinity KW - Selaginella Y1 - 2012 U6 - https://doi.org/10.3389/fpls.2012.00167 SN - 1664-462X VL - 3 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Gonzalez, Wendy A1 - Riedelsberger, Janin A1 - Morales-Navarro, Samuel E. A1 - Caballero, Julio A1 - Alzate-Morales, Jans H. A1 - Gonzalez-Nilo, Fernando D. A1 - Dreyer, Ingo T1 - The pH sensor of the plant K+-uptake channel KAT1 is built from a sensory cloud rather than from single key amino acids JF - The biochemical journal N2 - The uptake of potassium ions (K+) accompanied by an acidification of the apoplasm is a prerequisite for stomatal opening. The acidification (approximately 2-2.5 pH units) is perceived by voltage-gated inward potassium channels (K-in) that then can open their pores with lower energy cost. The sensory units for extracellular pH in stomatal K-in channels are proposed to be histidines exposed to the apoplasm. However, in the Arabidopsis thaliana stomatal K-in channel KAT1, mutations in the unique histidine exposed to the solvent (His(267)) do not affect the pH dependency. We demonstrate in the present study that His(267) of the KAT1 channel cannot sense pH changes since the neighbouring residue Phe(266) shifts its pK(a) to undetectable values through a cation-pi interaction. Instead, we show that Glu(240) placed in the extracellular loop between transmembrane segments S5 and S6 is involved in the extracellular acid activation mechanism. Based on structural models we propose that this region may serve as a molecular link between the pH- and the voltage-sensor. Like Glu(240), several other titratable residues could contribute to the pH-sensor of KAT1, interact with each other and even connect such residues far away from the voltage-sensor with the gating machinery of the channel. KW - Arabidopsis thaliana KW - channel protein structure KW - channel protein-proton interaction KW - KAT1 KW - pH regulation KW - potassium chanel Y1 - 2012 U6 - https://doi.org/10.1042/BJ20111498 SN - 0264-6021 VL - 442 IS - 7 SP - 57 EP - 63 PB - Portland Press CY - London ER - TY - CHAP A1 - Gonzalez, W. A1 - Riedelsberger, J. A1 - Morales-Navarro, S. E. A1 - Caballero, Julio A1 - Alzate-Morales, Jans H. A1 - Gonzalez-Nilo, F. D. A1 - Dreyer, Ingo T1 - The pH sensor of the plant K plus uptake channel KAT1 is built from a sensory cloud rather than from single key amino acids T2 - The FEBS journal Y1 - 2012 SN - 1742-464X VL - 279 SP - 455 EP - 455 PB - Wiley-Blackwell CY - Hoboken ER -