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Ionotropic glutamate receptors (iGluRs) in the animal Central Nervous System are vital for high fidelity synaptic transmission. Glutamate, the principal neurotransmitter, binds to an extracellular ligand-binding domain to open the transmembrane ion channel. This action drives a depolarization of the postsynaptic membrane and promotes Ca²⁺ transport. GLutamate Receptor-like channels (GLRs) are the plant homologs of iGluRs and are also associated with electrical and Ca²⁺ signaling to participate in essential mechanisms, including developmental processes, responses to (a)biotic stress, sexual reproduction, and systemic signaling. The evolutionary relationship between iGluRs and GLRs was recently verified, finding structural homology in the extracellular ligand-binding domain (LBD) — yet the structure-function relationships of GLRs are only emerging. I'll present and discuss data on the characterization of GLRs expressed in moss protonema and  heterologous systems, demonstrating the requirements for functional ion channel operation and the channel properties that distinguish GLRs from iGluRs. With a structurally conserved ligand-binding domain, albeit conferring different ligand-gating properties, we show the GLR ion channel pore plays a direct role in ion channel gating and ion selectivity. We further address the conservation of these properties in Arabidopsis GLRs, and address the vexing problem created by the diversification and strong expansion of GLRs in flowering plants. These results aim to enlighten the molecular evolution of plant glutamate receptors shaping the ion channel properties that ultimately conserve a role in Ca²⁺ and electrical signaling and have strong implications in our current interpretation and understanding of GLRs biological functions.