Electrophysiological analyses conducted about 25 years ago detected two types of anion channels in the plasma membrane of guard cells. One type of channel responds slowly to changes in membrane voltage while the other responds quickly. Consequently, they were named SLAC, for SLow Anion Channel, and QUAC, for QUick Anion Channel. Recently, genes SLAC1 and QUAC1/ALMT12, underlying the two different anion current components, could be identified in the model plant Arabidopsis thaliana. Expression of the gene products in Xenopus oocytes confirmed the quick and slow current kinetics. In this study we provide an overview on our current knowledge on slow and quick anion channels in plants and analyze the molecular evolution of ALMT/QUAC-like and SLAC-like channels. We discovered fingerprints that allow screening databases for these channel types and were able to identify 192 (177 non-redundant) SLAC-like and 422 (402 non-redundant) ALMT/QUAC-like proteins in the fully sequenced genomes of 32 plant species. Phylogenetic analyses provided new insights into the molecular evolution of these channel types. We also combined sequence alignment and clustering with predictions of protein features, leading to the identification of known conserved phosphorylation sites in SLAC1-like channels along with potential sites that have not been yet experimentally confirmed. Using a similar strategy to analyze the hydropathicity of ALMT/QUAC-like channels, we propose a modified topology with additional transmembrane regions that integrates structure and function of these membrane proteins. Our results suggest that cross-referencing phylogenetic analyses with position-specific protein properties and functional data could be a very powerful tool for genome research approaches in general.
Keywords: anion channel, evolution, SLAC/SLAH, ALMT, QUAC, voltage dependent, topology, phosphorylation
Citation: Dreyer I, Gomez-Porras JL, Riaño-Pachón DM, Hedrich R and Geiger D (2012) Molecular evolution of slow and quick anion channels (SLACs and QUACs/ALMTs). Front. Plant Sci. 3:263. doi: 10.3389/fpls.2012.00263
Received: 17 June 2012; Accepted: 12 November 2012;
Published online: 29 November 2012.
Edited by:Markus Geisler, University of Fribourg, Switzerland
Reviewed by:Sebastien Thomine, Centre National de la Recherche Scientifique, France
Copyright: © 2012 Dreyer, Gomez-Porras, Riaño-Pachón, Hedrich and Geiger. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Ingo Dreyer, Plant Biophysics, Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid, Campus de Montegancedo, Carretera M-40, km 37.7, Pozuelo de Alarcón, Madrid E-28223, Spain. e-mail: firstname.lastname@example.org