Structural and functional insights into core ABA signaling.

A series of papers in the last year reported major advances in our understanding of abscisic acid (ABA) signaling: the identification of soluble ABA receptors, the elucidation of a core ABA signaling pathway and structural insights into the mechanism of ABA perception and signaling. Here we summarize these advances, which have shown in atomic resolution that the ABA receptors PYR1, PYL1 and PYL2 function as allosteric switches that inhibit type 2C protein phosphatases (PP2Cs) in response to ABA. These receptors function at the apex of a core signaling pathway that regulates ABA responses by controlling SnRK2 kinase activity and the phosphorylation of downstream target proteins such as ABFs, which control nuclear responses, and the ion channel SLAC1, which mediates electrophysiological responses to ABA.