ABA perception and signalling.

Plant productivity is continuously challenged by pathogen attack and abiotic stress such as drought and salt stress. The phytohormone abscisic acid (ABA) is a key endogenous messenger in plants' responses to such stresses and understanding ABA signalling is essential for improving plant performance in the future. Since the discovery of ABA as a leaf abscission- and seed dormancy-promoting sesquiterpenoid in the 1960s, our understanding of the action of the phytohormone ABA has come a long way. Recent breakthroughs in the field of ABA signalling now unfold a unique hormone perception mechanism where binding of ABA to the ABA receptors RCARs/PYR1/PYLs leads to inactivation of type 2C protein phosphatases such as ABI1 and ABI2. The protein phosphatases seem to function as coreceptors and their inactivation launches SNF1-type kinase action which targets ABA-dependent gene expression and ion channels.