A Central Role of Abscisic Acid in Stress-Regulated Carbohydrate Metabolism Stefan Kempa1¤, Julia Krasensky1, Silvia Dal Santo1, Joachim Kopka2, Claudia Jonak1* 1 Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, Vienna, Austria, 2 Max Plank Institute of Molecular Plant Physiology, Golm, Germany Abstract Background: Abiotic stresses adversely affect plant growth and development. The hormone abscisic acid (ABA) plays a central role in the response and adaptation to environmental constraints. However, apart from the well established role of ABA in regulating gene expression programmes, little is known about its function in plant stress metabolism. Principal Findings: Using an integrative multiparallel approach of metabolome and transcriptome analyses, we studied the dynamic response of the model glyophyte Arabidopsis thaliana to ABA and high salt conditions. Our work shows that salt stress induces complex re-adjustment of carbohydrate metabolism and that ABA triggers the initial steps of carbon mobilisation. Significance: These findings open new perspectives on how high salinity and ABA impact on central carbohydrate metabolism and highlight the power of iterative combinatorial approaches of non-targeted and hypothesis-driven experiments in stress biology. Citation: Kempa S, Krasensky J, Dal Santo S, Kopka J, Jonak C (2008) A Central Role of Abscisic Acid in Stress-Regulated Carbohydrate Metabolism. PLoS ONE 3(12): e3935. doi:10.1371/journal.pone.0003935 Editor: Ivan Baxter, Purdue University, United States of America Received July 4, 2008; Accepted November 14, 2008; Published December 12, 2008 Copyright: 2008 Kempa et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the Austrian Science Fund (FWF), the Vienna Science and Technology Fund (WWTF) and GEN-AU. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: claudia.jonak@gmi.oeaw.ac.at ¤ Current address: Max Plank Institute of Molecular Plant Physiology, Golm, Germany Introduction High soil salinity is a major environmental constraint for plant growth and development, and limits agronomic yield [1]. Salt stress affects almost all aspects of plant physiology. A decrease in water availability constitutes the primary limitation and leads to osmotic stress. In the second phase, high concentrations of sodium ions are toxic to the cell as they inhibit essential enzymes, cell division and expansion. Membranes may become disorganised and excess levels of reactive oxygen species (ROS) are produced, leading to oxidative stress [2–4]. Genetic and biochemical studies indicate that distinct signal transduction pathways mediate different aspects of high salt stress, which ultimately lead to reprogramming of metabolism, physiol- ogy and morphology [5]. Recovery of ion balance under salinity can be achieved by restriction of entry, vacuolar compartmental- isation and extrusion of sodium from the cell. For osmotic adjustment, plants can accumulate osmoprotective compounds such as proline, glycine betaine, sugars and sugar alcohols [6]. Additionally, compatible solutes appear to play a beneficial role by stabilising membranes and proteins, preserving the activity of enzymes and scavenging ROS [7]. Salinity has a strong impact on gene expression [8–11]. Salt stress-inducible genes comprise genes that directly protect cells from stress and genes that code for regulatory proteins. The first group includes genes involved in the synthesis of osmoprotectants, detoxification enzymes, ion channels and transporters, whereas the second group comprises genes encoding protein kinases and phosphatases, transcription factors, and enzymes required for the synthesis of the hormone abscisic acid (ABA). ABA is an important regulator in many aspects of plant growth and development, and is pivotal for stress resistance [12–14]. Interestingly, ABA also plays a recently discovered role in hydroid regeneration, stress-adaptation in sponges, pathogenesis of Toxo- plasma gondii and in human immune responses, thus indicating a conservation of ABA signalling across kingdoms [15–18]. In plants, ABA accumulates in response to different environmental stresses such as high salt, cold and drought. ABA-deficient plants have a modified tolerance to high salt conditions [19–21]. ABA appears to be perceived at several sites both extracellularly and intracellularly [22–24]. Phospholipids, heterotrimeric G proteins, modulation of intracellular calcium levels and the action of protein kinases and phosphatases are involved in ABA signalling [25,26]. As an integral part of stress signal transduction, ABA regulates important cellular reactions such as stomatal closure and gene expression. Based on the observation that only a subset of stress- inducible genes responds to ABA, ABA-dependent and indepen- dent regulatory pathways have been suggested to mediate stress response [27]. Although global adjustment of metabolism is vital for adaptation to high salinity, our knowledge of the mechanisms involved in metabolic adaptation upon adverse environmental conditions is scarce. Early events largely determine whether plants can cope with stress [28] and point to the mechanisms plants use to adapt. PLoS ONE | www.plosone.org 1 December 2008 | Volume 3 | Issue 12 | e3935