Aluminum-Activated Malate Transporters Can Facilitate GABA Transport.

Plant aluminum-activated malate transporters (ALMTs) are currently classified as anion channels; they are also known to be regulated by diverse signals, leading to a range of physiological responses. Gamma-aminobutyric acid (GABA) regulation of anion flux through ALMT proteins requires a specific amino acid motif in ALMTs that shares similarity with a GABA binding site in mammalian GABA receptors. Here, we explore why TaALMT1 activation leads to a negative correlation between malate efflux and endogenous GABA concentrations ([GABA]) in both wheat () root tips and in heterologous expression systems. We show that TaALMT1 activation reduces [GABA] because TaALMT1 facilitates GABA efflux but GABA does not complex Al TaALMT1 also leads to GABA transport into cells, demonstrated by a yeast complementation assay and via C-GABA uptake into -expressing oocytes; this was found to be a general feature of all ALMTs we examined. Mutation of the GABA motif (TaALMT1) prevented both GABA influx and efflux, and resulted in no correlation between malate efflux and [GABA] We conclude that ALMTs are likely to act as both GABA and anion transporters in planta. GABA and malate appear to interact with ALMTs in a complex manner to regulate each other's transport, suggestive of a role for ALMTs in communicating metabolic status.