Salinity-regulated expression of genes involved in GABA metabolism and signaling

4-Aminobutyrate (GABA) is a nonproteinogenic amino acid that functions in stress tolerance and signaling. Here, we report that salinity stress and elevated GABA levels coincided with the induction of glutamate decarboxylase 4 (GAD4) expression in Arabidopsis thaliana (L.) Heynh. ecotype Col-0. In-silico and microarray analysis revealed the over-representation of binding sites for WRKY and MYB transcription factors in the GAD4 promoter, as well as their co-expression with GAD4. Transcript profiling of liquid culture-grown, wild-type plantlets subjected to salinity stress for up to two days confirmed that GAD4 expression is associated with the inducible co-expression of WRKY28, WRKY30, WRKY40, MYB2, MYB15, and MYB108, as well as calmodulin-like 37 and aluminum-activated malate transporter 2, suggesting the involvement of gene regulation, protein activation, and anion transport in GABA accumulation. Transcript profiling of shoots from soil-grown, wild-type plants and corresponding single and double GAD mutants subjected to two days of salinity stress suggests that the GABA accumulation could involve post-translational activation of pre-existing GAD1 and GAD2 by elevated cytosolic calmodulin, as well as induction of GAD4 expression.