AtGLR3.4, a glutamate receptor channel-like gene is sensitive to touch and cold

Abstract

The Arabidopsis genome encodes for 20 members of putative ligand-gated channels, termed glutamate receptors (GLR). Despite the fact that initial studies suggested a role for GLRs in various aspects of photomorphogenesis, calcium homeostasis or aluminium toxicity, their functional properties and physiological role in plants remain elusive. Here, we have focussed on AtGLR3.4, which is ubiquitously expressed in Arabidopsis including roots, vascular bundles, mesophyll cells and guard cells. AtGLR3.4 encodes a glutamate-, touch-, and cold-sensitive member of this gene family. Abiotic stress stimuli such as touch, osmotic stress or cold stimulated AtGLR3.4 expression in an abscisic acid-independent, but calcium-dependent manner. In plants expressing the Ca(2+) -reporter apoaequorin, glutamate as well as cold elicited cytosolic calcium elevations. Upon glutamate treatment of mesophyll cells, the plasma membrane depolarised by about 120 mV. Both glutamate responses were transient in nature, sensitive to glutamate receptor antagonists, and were subject to desensitisation. One hour after eliciting the first calcium signal, a 50% recovery from desensitisation was observed, reflecting the stimulus-induced fast activation of AtGLR3.4 transcription. We thus conclude that AtGLR3.4 in particular and GLRs in general could play an important role in the Ca(2+) -based, fast transmission of environmental stress.

Glutamate Receptor Subtypes Evidenced by Differences in Desensitization and Dependence on theGLR3.3andGLR3.4Genes

“…An assumption at the outset was that different members of the 20-gene GLR family would be found to function in the hypocotyl and root if both organs were studied with similar techniques. Figure 1A shows that application of Gly to lightgrown hypocotyls caused a large, transient membrane depolarization, similar to previously reported measurements in roots (Qi et al, 2006) and reminiscent of recordings made in mesophyll cells (Meyerhoff et al, 2005). Figure 1B summarizes 88 similar measurements of Gly-triggered transient depolarizations.…”

“…These roles include regulation of hypocotyl elongation (Lam et al, 1998;Dubos et al, 2003), sensing of mineral nutrient status (Kim et al, 2001), regulating carbon/nitrogen balance (Kang and Turano, 2003), resisting aluminum toxicity (Sivaguru et al, 2003) and cold (Meyerhoff et al, 2005), root meristem function (Li et al, 2006;Walch-Liu et al, 2006), as well as jasmonate-mediated defense mechanisms (Kang et al, 2006).…”

Sodium as nutrient and toxicant

“…2). Other such possible routes include nonselective cation channels (NSCCs), such as the cyclic nucleotide gated (CNGC) and/or glutamate receptor (GLR) channels (Lemtiri-Chlieh and Berkowitz 2004;Meyerhoff et al 2005;Wolf et al 2005;Zhao et al 2011; see also Véry et al 1998;Tyerman and Skerrett 1999). It is also possible that members of the KUP/HAK/KT family, generally attributed to primary K + uptake in roots (Gierth and Mäser 2007), might contribute, as these have been shown to be capable of mediating low-affinity Na + fluxes in roots under special circumstances (Santa-María et al 1997;Takahashi et al 2007; see also Mäser et al 2002), and are also expressed in shoots (Kim et al 1998;Rubio et al 2000;Bañuelos et al 2002;Su et al 2002).…”

Roles of ion channels and transporters in guard cell signal transduction

“…GLR3.4 is ubiquitously expressed throughout the plant, including guard cells, and so may play role in Ca 2+ -based guard cell signaling [115].…”