Abscisic acid binds to recombinant Arabidopsis thaliana G-protein coupled receptor-type G-protein 1 in Sacaromycese cerevisiae and in vitro

• G-protein coupled receptor-type G-proteins (GTGs) are proposed to be abscisic acid receptors.
• However, reports in the literature are inconsistent on this point.
• We examined the interaction of abscisic acid with a recombinant form of GTG.
• A physiologically relevant binding affinity is determined for abscisic acid binding to GTG.
• This independent study confirms the ability of GTGs to bind abscisic acid in vitro and in yeast.

The G-protein coupled receptor-type G-proteins (GTG) 1 and 2 from Arabidopsis thaliana have been proposed to function in the modulation of abscisic acid (ABA) mediated responses to stress and development. In particular it has been suggested that they function as ABA receptors based on in planta and in vitro analyses. However a recent independent report was inconsistent with this, suggesting that there is no link between the GTGs and ABA in planta. Here we provide an independent assessment of the ability of ABA to bind to recombinant GTG1 in vitro and in vivo in Sacaromycese cerevisiae. Radio-labelled binding assays on enriched lipid-reconstituted recombinant GTG1, demonstrated specific concentration dependent binding of [3H]-ABA with a dissociation constant (KD) of 80 nM, corroborating previous reports. Assessment of the binding of [3H]-ABA to intact GTG1 expressing yeast, showed GTG1-dependent binding in vivo, yielding a physiologically relevant KD of 0.6 μM. Together these results provide independent evidence of a binding-interaction between ABA and GTG1 in vitro and in vivo, in support of the previously proposed possibility of a biologically relevant interaction between GTG1 and ABA.