Amino acids, an essential component that constitutes proteins in vivo, are also known to play as a signaling molecule that regulates various physiological functions in the living organism. Ionotropic glutamate receptors (iGluRs) are ligand-gated channels that specifically transmit amino acid signals in the central nervous system. Surprisingly, homologs of iGluRs, known as glutamate receptor-like channels (GLRs), were also found in higher plant genomes. However, their physiological roles or molecular functions are still obscure. Here, I review the latest research of plant GLRs and discuss their roles in plant signaling including environmental adaptation and cell-to-cell communications.