| Glutamate receptor genes in Arabidopsis (AtGLR ) were first identified based on their sequence similarity to animal ionotropic glutamate receptor genes (iGluR). Animal iGluRs encode ligand-gated ion channels that are important in neurotransmission, and have been implicated in human diseases, including Alzheimer's disease, Parkinson's disease, schizophrenia and excitotoxicity. The discovery of plant glutamate receptor genes raises an interesting question concerning their function in an organism without a nervous system. Pharmacological and reverse genetics approaches have been used to dissect the in vivo function of AtGLR genes in plants. So far, AtGLR genes have been proposed to be involved in light signal transduction, and the regulation of calcium homeostasis as well as carbon/nitrogen metabolism. With the completion of the Arabidopsis genome-sequencing project, a large gene family of twenty AtGLR genes has been identified. Here, I present detailed sequence and phylogenetic analysis of the ionotropic glutamate receptor family in prokaryotes and eukaryotes, including both plants and animals. I also attempt to further dissect the in vivo function of AtGLR genes by (1) performing the first comprehensive organ-specific expression analysis of the AtGLR gene family, and (2) analyzing gene function by reverse genetics approaches. Finally, I examine whether AtGLR genes encode functional ligand-gated ion channel subunits, as in the case of animal iGluRs, and try to explore the connection between the biochemical function of GLR proteins, i.e., channel activities, and their function in vivo. |
