PYR/PYL/RCAR ABA receptors

Abstract

The clade A protein phosphatases type 2C (PP2Cs) ABA INSENSITIVE 1 (ABI1) and ABI2 were the first components of the ABA signaling pathway identified from single-locus dominant mutations but functional redundancy precluded the identification of ABA receptors by classical forward genetic analyses. However, a chemical genetic approach using a synthetic selective ABA agonist, pyrabactin, led to the discovery of PYRABACTIN RESISTANCE1 (PYR1)/PYR1-LIKE (PYL1-13) ABA receptors. Independently, the search for interacting partners of clade A PP2Cs in yeast-two hybrid screenings also led to their discovery, naming them as REGULATORY COMPONENTS OF ABA RECEPTORS (RCAR1-14). From 2009 many studies have shed light on the biochemical properties of PYR/PYL/RCAR ABA receptors and their capability to inhibit clade A PP2Cs, the key negative regulators of the pathway. Physiological studies have made use of mutants impaired in several PYR/PYL/RCAR genes in order to break functional redundancy, and in the appropriated biological context, some specific functions of the receptors have also emerged. The regulation of their half-life through interaction with E3 ubiquitin ligases and the discovery of post-translational modifications of ABA receptors have been active fields as well. It is particularly appealing that ABA perception by PYL8 leads to reduced ubiquitination and specific stabilization of this unique receptor. More recently, translational studies in crops are starting to be developed and biotechnological applications are expected in the next years. The structural studies performed with Arabidopsis receptors are being complemented with studies in other plant species, which offer new insights on the mechanism of ABA perception that highlight the role of PP2Cs as co-receptors.