PROJECT SUMMARY
Despite not having a nervous system, plants have exceptional capacities to communicate between cells
and organs. Being sessile, this is vital for adaptation to animal herbivory (organ regeneration), extreme
temperatures, pathogens at all levels, etc. Interestingly, plants have evolved an expanded family of
glutamate receptors, proteins gated by glutamate to generate electric and calcium signals, which are well
known for their crucial role in the human nervous system and many of its related pathologies. My lab has
been leading the field of plant GLutamate Receptor (GLR) research. We pioneered their demonstration as
ion channels involved in cell-cell communication, and, among other, further studied their evolution, roles
in sexual reproduction, or functions of GLR-associated regulatory proteins. Under grant R01GM131043
we extended our scope to generate the first structural views of GLRs. Cryo-EM revealed a surprising
conservation of structural mechanisms with their animal homologues (iGluRs) but also many differences,
e.g. ligand promiscuity, non-canonical gating properties and different ionic selectivity. Globally these
features revealed functions in electrical communication and ligand-gated Ca2+ store homeostasis for GLRs.
Taking advantage of novel methodology that permits reasonable prediction from sequence and
homologous structures, we are now re-iterating GLR function and their physiological roles by generating
protein activity predictions by structural and molecular dynamics computational simulations. Specifically,
we are targeting ligand specificity, structural topologies affecting gating and de-sensitization speeds, and
ion selectivity. We posit these properties to be crucial for GLR-based physiology and will explore this
strategy to break the barrier posed by genetic/functional redundancy resulting from the elevated gene copy
number (20 in Arabidopsis, many more in other plants; 14 in humans). Our current efforts are focused in
developing these approaches and establishing new protocols for validation of structural predictions from
modeling. These will include validation of altered GLR properties by expression of combinations of mutated
glutamate receptors and accessory proteins on heterologous systems. Modifications likely to generate
either dominant-negative or -positive functional phenotypes will be knocked into our reference collection
of GLR mutants and screened for function. We will target complementation of backgrounds with multiple
mutations in diverse clades, and will screen for plausible functions of GLR roles, namely innate immunity,
organ regeneration and abiotic stresses. Ion imaging and single-cell transcriptomics of promising lines will
be further investigated for signaling and transcriptional pathways which are affected by GLR function.
Given that plant GLRs evolved physiological functions out of topologies and motifs that are associated
with disease when present in human glutamate receptors, notably in the “orphan” Glu-∂ sub-family, our
results should also address intriguing medical questions related to these structural aspects.
