ATGLR3.7 AS NEGATIVE REGULATOR OF ATGLR3.3 MEDIATED STRESS RESPONSES

During evolution, plants have developed sophisticated mechanisms to perceive and respond to environmental cues. Adaptability and responsivity to biotic and abiotic stresses involve a complex interplay of multiple factors: second messengers, phytohormones, metabolites and a whole variety of molecules involved into the perception, distribution, and transduction of stress signals. Recent studies have demonstrated that wounding-driven long-distance propagation of Ca2+ waves depend on the activity of the cation permeable channel Glutamate Receptor-Like 3.3 (GLR3.3), but the mechanisms regulating this crucial factor remain largely unknown. GLRs are homologous to the animals’ ionotropic glutamate receptor channels (iGluRs), which can form both homo and hetero-tetramer. This allows us to hypothesize that different assemblies of plant GLRs as well can bring to the formation of channels with different properties. Here we present multiple lines of evidence supporting the molecular and functional interdependency between GLR3.3 and another relatively uncharacterized GLR isoform, GLR3.7. Preliminary data in our laboratory indicate that GLR3.7 activity can negatively impact GLR3.3-mediated responses, such as burning and exogenous amino acid administration, suggesting this GLR isoform as a putative partner of GLR3.3. Colocalization and close proximity of GLR3.3 and GLR3.7, both at tissue and cellular level, has been demonstrated by GUS reporter assay, complemented by a FLIM analysis. Moreover, Co-Immunoprecipitation experiments demonstrated direct protein-protein interaction between the two GLRs. Intriguingly, expression of the cation permeable GLR3.3 channel exhibits a negative impact on yeast G19 sodium sensitive strain growth efficiency, significantly rescued by GLR3.7 expression, indicating a wider influence of GLR3.7 on GLR3.3 activity. To investigate the relationship between GLR3.3 and GLR3.7 activity in response to changes of natural environmental conditions, we developed a new protocol to study the effect of re-watering drought-stressed plants. In this scenario, GLR3.3 showed again a crucial role in the generation and propagation of long-distance Ca2+ waves, whereas GLR3.7 exerts a negative regulatory role. In summary, our results suggest that GLR3.7 can modulate the activity of GLR3.3 by possibly forming, in planta, a heteromeric channel.