Plant Ion Channels: Gene Families, Physiology, and Functional Genomics Analyses

Abstract

Distinct potassium, anion, and calcium channels in the plasma membrane and vacuolar membrane of plant cells have been identified and characterized by patch clamping. Primarily owing to advances in Arabidopsis genetics and genomics, and yeast functional complementation, many of the corresponding genes have been identified. Recent advances in our understanding of ion channel genes that mediate signal transduction and ion transport are discussed here. Some plant ion channels, for example, ALMT and SLAC anion channel subunits, are unique. The majority of plant ion channel families exhibit homology to animal genes; such families include both hyperpolarization-and depolarization-activated Shaker-type potassium channels, CLC chloride transporters/channels, cyclic nucleotide–gated channels, and ionotropic glutamate receptor homologs. These plant ion channels offer unique opportunities to analyze the structural mechanisms and functions of ion channels. Here we review gene families of selected plant ion channel classes and discuss unique structure-function aspects and their physiological roles in plant cell signaling and transport.

A rice high-affinity potassium transporter (HKT) conceals a calcium-permeable cation channel

“…However, oocytes expressing OsHKT2;4 generated currents that were large and time-dependent when applying highly hyperpolarized pulses. The current-voltage relationship displayed strong inward rectification with a profile reminiscent of numerous voltage-gated ion channels, including well-known K + channels in the Shaker family (16,17). Also surprising was the tail current recorded at the 0 mV that displayed an initial rapid increase in amplitude followed by a slow decay (Fig.…”

MscS-Like10 is a stretch-activated ion channel from Arabidopsis thaliana with a preference for anions

“…17). In planta, MSL10 gating could lead to the activation of depolarization-activated Shaker-type potassium channels and depolarization-activated Ca 2+ channels, leading to K + efflux from the cell, Ca 2+ influx, and possibly the propagation of a systemic signal (55,56). Thus, the electrophysiological characterization of a MscS homolog from a multicellular system opens up the exciting possibility that some members of this family of MS channels may not only release osmolytes from swelling cells and organelles, but also alter cell physiology and potentially participate in intercellular signaling.…”

Heteromeric AtKC1·AKT1 Channels in Arabidopsis Roots Facilitate Growth under K+-limiting Conditions

“…The fresh weight as well as the root length of WT and mutant seedlings was determined after 11 days of seedling growth under a 12/12-h light to dark rhythm. 2 mM NH 4 ϩ was added to the medium to inhibit transporter-mediated K ϩ uptake (11,12,15). Root length and the fresh weight of at least 20 seedlings were measured at each condition in three independent experiments (ϮS.D.…”

“…Classical experiments by Epstein et al in 1963 (2) described K ϩ root uptake as a biphasic process mediated by two uptake mechanisms: high affinity potassium transport with apparent affinities of ϳ20 M and a low affinity transport system with K m values in the millimolar range. During the last decades several molecular components of potassium transport systems have been identified and functionally characterized in plants (3,4). Mutant analyses, heterologous expression, as well as radiotracer uptake experiments characterized the K ϩ channels AKT1⅐AtKC1 and members of the HAK⅐KT⅐KUP family as major components of the Arabidopsis thaliana root-localized potassium transport system (5)(6)(7)(8)(9).…”