Abscisic Acid Catabolism Generates Phaseic Acid, a Molecule Able to Activate a Subset of ABA Receptors

Abstract

Abscisic acid (ABA) catabolic pathways are conventionally thought of as routes for ABA inactivation and, thus, reduction of the well-known ABA responses to cope with stress. However, this point of view was challenged by the finding that some forms of hydroxylated ABA generated by ABA catabolism still maintain biological activity (Zou et al., 1995; Kepka et al., 2011). Hydroxylation at C-8′ position is thought to be the predominant ABA catabolic pathway, and this reaction is catalyzed by the CYP707A family cytochrome P450 monooxygenases (P450s) (Krochko et al., 1998; Kushiro et al., 2004; Saito et al., 2004) (Figure 1).