Structure and Mechanism of Hormone Perception and Signal Transduction by Abscisic Acid Receptors

Abstract

Abscisic acid (ABA) is a vital plant hormone that confers abiotic stress tolerance. ABA acts through inhibition of certain members of the type 2C protein phosphatase (PP2C), resulting in activation of the SNF1-related kinases (SnRKs) that positively transduce the ABA signal. The identity of ABA receptors had been elusive until recent studies identified the PYR/PYL/RCAR (PYL) family of proteins as promising candidates. In this study, the structures of representative PYL members in apo and ABA-bound forms, as well as in complexes with PP2Cs were determined using X-ray crystallography. Analyses of these structures revealed the molecular mechanisms of how PYL senses ABA and transduces the signal to PP2C inhibition. Additional structure determination of PYL in complexes with pyrabactin, a selective ABA agonist, provided mechanistic insights of how these receptors can be selectively activated or repressed. These findings have valuable ramifications in agriculture and contribute to our understanding of hormone receptor signalling.