Functional characterisation of Arabidopsis glutamate-like receptors
 
Matthew Gilliham1,*, Lai-hua Liu1, Pauline Essah1, Romola Davenport1, Mark Tester2 and Julia Davies1
1 Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK
2 Australian Centre for Plant Functional Genomics & University of Adelaide, PMB1, Glen Osmond, South Australia, 5074, Australia
*email: mg253@cam.ac.uk
 
There are twenty members of the Arabidopsis glutamate-like receptor family (AtGLR) that have been so named as they share significant similarity with the animal ionotropic glutamate receptors (iGLuR). Animal iGLuR are non-selective cation channels that have been demonstrated to function predominately as Ca2+ and Na+ influx pathways, particularly at synaptic junctions. Although it is predicted that AtGLR have the 3+1 channel-like structure of iGLuR, and they also share a ligand-binding domain of significant similarity to the animal iGluR, the amino acid sequence within the putative pore of AtGLR is unlike any other known channel. This makes predictions of AtGLR selectivity, if they are indeed ion channels, impossible. In an attempt to determine AtGLR function, the expression of several members of the family has been attempted in Xenopus oocytes, a popular expression system for iGLuR.
Preliminary results indicating successful heterologous expression and characterisation of AtGLR as Ca2+, K+ and Na+ permeable ion channels have been reported at several conferences over the last five years. So far, however, these reports have not been successfully published in peer reviewed journals. iGLuR form functional channels by combining subunits into hetero- or homo-tetramers therefore, as well as the expression of single members of the AtGLR family we are undertaking co-expression studies to screen for AtGLR function. The utility and difficulty of using Xenopus oocytes as an heterologous expression system for plant ion channels and transport proteins will therefore be discussed with reference to our own attempts to characterise AtGLRs.
In the light of difficulties in the definitive functional characterisation of the AtGLRs in heterologous systems, we are also turning our attention to the plant resource and conducting electrophysiological studies in planta in an attempt to elucidate AtGLR function.
 
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