Structural and functional diversity of glutamate receptors-like channels in plants

Glutamate receptor-like (GLR) family encodes cation-permeable ion channels that are crucial for defense signaling and have attracted significant research interest. The identification of multiple GLRs subfamilies across vascular lineages suggests their functional diversity in plants. Functional studies of clade 3 GLRs confirm their critical role in generating electrical signals and increasing cytosolic Ca²⁺ in response to mechanical wounding, insect and pathogen attacks, and other environmental cues for systemic defense responses. In this review, we present evidence that GLRs are conserved across all plant lineages and likely originated from Streptophyta. Comparative bioinformatic analysis of GLRs' functional domains reveals that ion channel gating and ligand binding of GLR are highly conserved and involved in ion transport and cell-to-cell communication in plants. The role of GLRs in electrical and Ca²⁺ signaling is also discussed in non-vascular tissues as well as in vascular plants. The hypothetical model suggests that GLR-induced systemic defense responses to external stimuli may have co-evolved with plant vascular systems. We also highlight the role of glutamate and other amino acid agonists in regulating membrane depolarization and cytosolic Ca²⁺ concentration. Finally, we review the roles of GLR in physiological processes, abiotic and biotic stresses, and strategies to enhance plant health and productivity.