ABA signal transduction at the crossroad of biotic and abiotic stress responses

Abstract

Abscisic acid (ABA) regulates key processes relevant to seed germination, plant development, and biotic and abiotic stress responses. Abiotic stress conditions such as drought induce ABA biosynthesis initiating the signalling pathways that lead to a number of molecular and cellular responses, among which the best known are the expression of stress-related genes and stomatal closure. Stomatal closure also serves as a mechanism for pathogen defence, thereby acting as a platform for crosstalk between biotic and abiotic stress responses involving ABA action. Significant advances in our understanding of ABA signal transduction have been made with combination of approaches including genetics, biochemistry, electrophysiology and chemical genetics. Molecular components associated with the ABA signalling have been identified, and their relationship in the complex network of interactions is being dissected. We focused on the recent progress in ABA signal transduction, especially those studies related to identification of ABA receptors and downstream components that lead ABA signal to cellular response. In particular, we will describe a pathway model that starts with ABA binding to the PYR/PYL/RCAR family of receptors, followed by inactivation of 2C-type protein phosphatases and activation of SnRK2-type kinases, and eventually lead to activation of ion channels in guard cells and stomatal closure. Plants are constantly bombarded by environmental signals including both biotic and abiotic stress condtions. Among the complex molecular mechanisms for responding to these signals, plant hormone ABA plays a key role in the crosstalk of signaling pathways that couple biotic and abiotic signals to cellular responses. Centrally located in the many signaling processes, ABA-induced stomatal closure controls both pathogen entry and water loss during drought stress. This review highlights recent breakthroughs that demonstrate the molecular events underlying ABA action in stomatal guard cells. © 2011 Blackwell Publishing Ltd.