Linking Metabolism to Membrane Signaling: The GABA–Malate Connection

γ-Aminobutyric acid (GABA) concentration increases rapidly in tissues when plants encounter abiotic or biotic stress, and GABA manipulation affects growth. This, coupled to GABA's well-described role as a neurotransmitter in mammals, led to over a decade of speculation that GABA is a signal in plants. The discovery of GABA-regulated anion channels in plants provides compelling mechanistic proof that GABA is a legitimate plant-signaling molecule. Here we examine research avenues unlocked by this finding and propose that these plant ‘GABA receptors’ possess novel properties ideally suited to translating changes in metabolic status into physiological responses. Specifically, we suggest they have a role in signaling altered cycling of tricarboxylic acid (TCA) intermediates during stress via eliciting changes in electrical potential differences across membranes.

Trendsγ-Aminobutyric acid (GABA), a non-protein amino acid, regulates the activity of aluminum-activated anion transporters (ALMTs); these, like mammalian GABAA receptors, are anion channels that alter the electrical potential across membranes.ALMTs are a multigenic protein family found in all plants that are involved in multiple physiological processes. Contrary to their name, most ALMTs are not activated by aluminum; instead, they are activated by anions and negatively regulated by GABA.ALMTs share little homology with mammalian GABAA receptors; the only region of similarity so far identified is a domain of 12 amino residues containing a phenylalanine or tyrosine required for GABA sensitivity.Malate activation and GABA inhibition of ALMTs provide a mechanism for indicating changes in tricarboxylic acid (TCA) cycle activity via membrane signaling and the propagation of these signals from cell to cell.