Structure and Mechanism of Abscisic Acid Signaling by Snf1-related Protein Kinase 2 (SnRK2) and Type 2C Protein Phosphatase (PP2C)

Abstract

Abscisic acid is a vital phytohormone that promotes abiotic stress tolerance in plants. The earliest events of the signaling pathway are believed to be mediated by the ABA receptors, type 2C phosphatase (PP2Cs), and Snf1-related kinases 2 (SnRK2s). Here, we elucidated the mechanism of SnRK2 autoactivation and the structural basis of its inhibition by PP2C. A two-step activation mechanism is established, involving the stabilization of kinase domain by a conserved intramolecular element SnRK2 box that aids in the subsequent auto-phosphorylation of activation loop. Inhibition of SnRK2 by PP2C requires the dephophorylation of activation loop and blockade of catalytic site by the phosphatase. Finally, structural information from the SnRK2?PP2C complex identifies molecular similarities with the receptor?PP2C complex, indicating the use of molecular mimicry to relay ABA binding to SnRK2 activation. The results address the gaps in our knowledge of ABA signaling and pave the way for future agricultural application.