Keeping in touch with plant glutamate receptors
 
Oliver Meyerhoff1, Katharina Müller1, M. Rob G. Roelfsema1, Andreas Latz1, Benoit Lacombe2, Rainer Hedrich1, Petra Dietrich3 and Dirk Becker1,*
1 University of Wuerzburg , Molecular Plant Physiology & Biophysics, Julius-von-Sachs-Platz 2, 97082 Wuerzburg , Germany
2 Biochimie et Physiologie Moleculaires des Plantes, UMR 5004, Agro-M/CNRS/INRA/UM2, F-34060 Montpellier Cedex 1, France
3 University of Erlangen, Institut für Molekulare Pflanzenphysiologie, Staudtstr. 5, 91058 Erlangen, Germany
*email: dbecker@botanik.uni-wuerzburg.de
 
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 of GLRs in various aspects of photomorphogenesis, calcium homeostasis or aluminium toxicity, their functional properties and physiological role in plants remain elusive. Here we 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 Ca2+-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 Ca2+-based, fast transmission of environmental stress.
 
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