Physiology and biophysics of plant ligand‐gated ion channels

Abstract

Small molecules and metabolites often act as intra- or extracellular messengers in signal transduction pathways. Ligand-gated ion channels provide a mean to transduce those biochemical signals at the membrane into electrical events and ion fluxes. In plants, cyclic nucleotides and glutamate represent intra- and extracellular signalling ligands, respectively. While the former have been shown to regulate voltage-dependent ion channels and are supposed to activate cyclic nucleotide gated (CNG) channels, the latter are perceived by ionotropic glutamate receptors (GLRs). This review summarises our current knowledge about CNG channels and glutamate receptors in plants and their proposed roles in plant development and adaptation to biotic and abiotic stresses.

Ca2+ Conduction by an Amino Acid-Gated Ion Channel Related to Glutamate Receptors

“…Slowest to accrue has been information about the intrinsic transport properties of a GLR protein (Dietrich et al, 2010). Heterologous expression followed by voltage-clamp analysis is typically the most reliable source of this information.…”

“…Asn and Ser and other amino acids are exuded by plant roots (Nguyen, 2003). GLR3.4 and other members of the GLR family are expressed in roots (Chiu et al, 2002;Roy et al, 2008;Dietrich et al, 2010). Exuded amino acids that reach the rhizosphere are believed to be quickly mineralized by microbial metabolism (Griffiths et al, 1999;Owen and Jones, 2001).…”

Multiple Calmodulin-binding Sites Positively and Negatively Regulate Arabidopsis CYCLIC NUCLEOTIDE-GATED CHANNEL12

“…Plant genomes examined to date lack homologs to animal voltage-gated cation channels and instead possess expanded families of ligand-gated cation channels, represented primarily by the ionotropic glutamate receptor-like channel and cyclic nucleotide-gated channel (CNGC) families (Mäser et al, 2001). CNGCs are nonselective cation channels that are hypothesized to function as Ca 2+ channels in plants (Dietrich et al, 2010;Jammes et al, 2011;Zelman et al, 2012) and are characterized by conserved structural components, including a short cytosolic N terminus, six transmembrane helices (S1-S6) with a pore-forming region between S5 and S6, and a cytosolic C terminus containing a cyclic nucleotide binding domain (CNBD; Kaupp and Seifert, 2002;Matulef and Zagotta, 2003). The CNBD mediates channel gating by cyclic nucleotide monophosphates such as cAMP and/or cGMP (Mäser et al, 2001;Kaupp and Seifert, 2002;Matulef and Zagotta, 2003;Kaplan et al, 2007;Zelman et al, 2012), though studies of this mechanism are largely restricted to animal isoforms.…”

High throughput chemical screening supports the involvement of Ca2+in cyclic nucleotide-gated ion channel-mediated programmed cell death in Arabidopsis

“…Since then, a substantial amount of work has been done to elucidate the molecular nature and biological functions of these channel proteins. 4,8 To date, the composition of these channel tetramers and the precise regulatory mechanisms of this channel group remain unknown. However, further biochemical, molecular and genetic analyses will likely provide us with a more comprehensive understanding of plant CNGCs.…”

“…4,8 Through Arabidopsis mutant screens, four CNGCs, AtCNGC 2, 4, 11 and 12, have been identified to be involved in immune responses. 8 The loss-of-function mutants of AtCNGC2 and 4 (dnd1 and dnd2/hlm1, respectively), exhibit increased resistance to pathogen infection but fail to induce a hypersensitive response (HR) after infection with some avirulent pathogens.…”