Abscisic acid (ABA) signaling: Finding novel components off the beaten track

Abstract

The sesquiterpene abscisic acid (ABA) is an ancient universal stress response molecule. In plants, many ABA-dependent processes operate via the PYR/PYL/RCAR receptor complexes, however, there is evidence suggesting that not all plant responses operate through this mechanism. This is consistent with ABA responses in animals and humans which do not contain such receptors. We hypothesize that plant and animal proteomes harbour proteins with undiscovered ABA-binding sites and propose that carefully curated amino acid search motifs deduced from the binding sites of experimentally confirmed ABA-binding proteins can identify many more candidates in plant and animal proteomes many of which show folds that are compatible with ABA-binding. Plant candidates include annotated ABA downstream signaling components such as SnRK2.2 and SnRK2.6 and proteins with roles in protein folding and RNA polyadenylation, while candidates in the human proteome affect, among other processes, immune responses and tumor progression. If these candidates will eventually be experimentally validated, it will imply that the regulation and tuning of ABA-dependent processes is considerably more complex than hitherto suspected and it will also expand and help to clarify the role of ABA in animal systems.