TWO CLADE III GLUTAMATE RECEPTOR-LIKE ISOFORMS INVERSELY REGULATE LOCAL AND LONG-DISTANCE CA2+ SIGNALLING IN ARABIDOPSIS THALIANA

In the central nervous system, ionotropic Glutamate Receptors (iGluRs) are tetrameric ligand-gated non-selective cation channels. They have been linked to learning and memory as well as to neurodegenerative pathologies such as Alzheimer disease. Thus, they are among the best characterized channels in animals. Animals and plants share this class of proteins. Plant Glutamate Receptors-like (GLRs) have been implicated in stomata movement regulation, pollen tube growth, long-distance signalling, root development and defence against pathogens. However, to date few details are known about their basic properties and functions, such as binding activity, ion transportation, sub-cellular localization, subunits interaction, desensitization etc. My PhD project focused on two GLR isoforms in Arabidopsis thaliana, AtGLR3.3 and AtGLR3.7 (hereafter called ‘AtGLR3.x’). Being putative amino acids-gated Ca2+-permeable channels, I tested the hypothesis that the two isoforms could handle Ca2+ dynamics upon amino acids challenge. Remarkably, Arabidopsis Col-0 plants show a transient elevation of cytosolic Ca2+ at the root tip meristematic zone upon amino acids treatment. Ablation of the AtGLR3.3 abolished the increase of Ca2+ concentration whereas loss of-function mutants for AtGLR3.7 showed enhanced Ca2+ rises in response to amino acids. Additionally, when the double mutant glr3.3glr3.7 was challenged with amino acids, mirrored the glr3.3 null-response. These results strongly suggested that the two AtGLRs could assemble in a channel where GLR3.3 would act as main scaffold and GLR3.7 would negatively regulate the biophysical properties. Being AtGLR3.x also expressed in the vascular tissues and in the cells of the floral abscission zone, we also assayed the role of AtGLR3.x in the generation/propagation of long-distance Ca2+ waves that occurs between stems and inflorescence apexes of Arabidopsis plants subjected to flaming. In the future, our efforts will be aimed at understanding whether the predicted amino acid sensing of GLRs is also required for the long-distance signalization.