Growing evidence suggests that plant proteomes contain numerous proteins that specifically bind abscisic acid (ABA). Many of them are complex multidomain proteins where specific ABA-binding can cause biochemical and physiological changes. Here we show that the Arabidopsis thaliana K + transporter AtKUP5 contains both a functional cytoplasmic N-terminal adenylate cyclase (AC) enabling the synthesis of 3’,5’-cAMP from ATP and a C-terminal phosphodiesterase (PDE) that hydrolyses 3’,5’-cAMP to 5’-AMP. We found that ABA binds in a ligand-specific manner to the catalytic center of the PDE thereby causing a reduction of 3’,5’-cAMP hydrolysis in vitro . The hydrolytic activity of the PDE is ABA concentration-dependent, biphasic and requires the presence of an intact ABA-binding site similar to the one in the canonical Pyrabactin resistance 1/PYR-like/Abscisic acid receptors, with V max of 1.19 pmole min -1 μg -1 in the absence of ABA, increasing to 1.58 pmole min -1 μg -1 at 2 nM ABA, and decreasing to 0.75 pmole min -1 μg -1 at 50 nM ABA. These findings are therefore consistent with a direct role of ABA in PDE activity modulations and form a functional link between 3’,5’-cAMP signaling and K + flux. Furthermore, we predict that a growing number of such receptor-like proteins that specifically and directly interact with ABA will be discovered thereby uncovering complex and ancient layers of signaling and metabolic regulation.
Kwiatkowski et al. (2026) studied this question.