Sixteen years have passed since human aquaporin-1 (AQP1) was discovered as the first water channel, facilitating trans-membrane water fluxes. Subsequent years of research showed that the water channel AQP1 was only the tip of an iceberg; the iceberg itself being the ubiquitous super family of membrane intrinsic proteins (MIPs) that facilitate trans-membrane transport of water and an increasing number of small, water-soluble and uncharged compounds. Here we introduce you to the superfamily of MIPs and provide a summary about our gradually refined understanding of the phylogenetic relationship of its members. This volume is dedicated to the metalloids, a recently discovered group of substrates for a number of specific MIPs in a diverse spectrum of organisms. Particular focus is given to the essential boron, the beneficial silicon and the highly toxic arsenic. The respective MIP isoforms that facilitate the transport of these metalloids include members from several clades of the phylogenetic tree, suggesting that metalloid transport is an ancient function within this family of channel proteins. Among all the various substrates that have been shown to be transported by MIPs, metalloids take an outstanding position. While water transport seems to be a common function of many MIPs, single isoforms in plants have been identified as being crucially important for the uptake of boric acid as well as silicic acid. Here, the function seems not to be redundant, as mutations in those genes render plants deficient in boron and silicon, respectively.

Thomas P. Jahn is an Associate Professor and group leader at the Department of Agriculture and Ecology, Faculty of Life Sciences, University of Copenhagen. He studied biology at the University of Bonn, Germany. From early on in his scientific career he was interested in transport processes in plants and the molecular mechanisms behind these processes. More recently his group contributed to the field of aquaporin research culminating in the identification of several new substrates for members of this superfamily of channel proteins. The overall scope of his current research focuses on the elucidation of networks comprising molecular components engaged in the responses to nutritional stresses, including elements of transport, assimilation, storage and stress signaling. Gerd P. Bienert is currently a Marie Curie Fellow at the Institute of Life Science at the Université Catholique de Louvain in Louvain la Neuve, Belgium. His work focuses on the molecular characterisation of the intracellular trafficking and hetero-oligomerisation of aquaporins in plants. In 2008, he received his PhD in Molecular Plant Nutrition from the University of Copenhagen, Denmark. During his PhD, Gerd Patrick Bienert made significant advances in the scientific understanding on the substrate selectivity of plant aquaporins for uncharged solutes. The work resulted in the molecular identification of the first arsenite, antimonite and hydrogen peroxide channels in plants. Gerd P. Bienert studied biology at the Julius-Maximilians-University Würzburg and at the Technical University Darmstadt, Germany. During his education he emphasized molecular plant physiology and biophysics, genetics and biotechnology. His main research interests focus on the molecular transmembrane transport processes involved in the uptake, translocation and extrusion of compounds that are relevant for plant physiology. In addition, intracellular regulation and trafficking of the transport proteins themselves are also contemplated. In his home region, Tauber-Franken, he began to develop his enthusiastic curiosity for biology by exploring and studying nature. He became fascinated by insects, especially the members of the order of hymenoptera to which he still devotes his free-time. The existing overlap between entomology and botany has aroused his interest in understanding the physiology of plants.