GABA signalling in guard cells acts as a 'stress memory' to optimise plant water loss

The non-protein amino acid {gamma}-aminobutyric acid (GABA) has been proposed to be an ancient messenger for cellular communication conserved across biological kingdoms. GABA has well-defined signalling roles in animals; however, whilst GABA accumulates in plants under stress it has not been determined if, how, where and when GABA acts as an endogenous plant signalling molecule. Here, we establish that endogenous GABA is a bona fide plant signal, acting via a mechanism not found in animals. GABA antagonises stomatal movement in response to opening and closing stimuli in multiple plant families including dicot and monocot crops. Using Arabidopsis thaliana, we show guard cell GABA production is necessary and sufficient to influence stomatal aperture, transpirational water loss and drought tolerance via inhibition of stomatal guard cell plasma membrane and tonoplast-localised anion transporters. This study proposes a novel role for GABA - as a stress memory - opening new avenues for improving plant stress tolerance.