Phytohormone Signaling in Response to Drought

Under natural conditions, plants are often exposed to both biotic (pathogens, wounding, insects) and abiotic stresses (drought, salinity, heat, high or low temperature, UV light, heavy metals, ozone) simultaneously. Among the various abiotic stresses, drought along with salinity and alkalinity confers osmotic stress and causes major yield losses, with water scarcity (drought) contributing to maximum losses. On perceiving stress, plants respond by activating signal transduction cascades that interact with other pathways (phytohormones) for an optimal response for survival. Hormones also control the response to environmental factors, but do so by influencing each other at a biosynthesis or signaling level rather than by discrete pathways. This coordination leads to a network of signal transduction that integrates various inputs leading to a comprehensive output resulting in a physiological adaptation to stress. The points of hormones interacting with one another are where crosstalk occurs, which helps in switching the response from one pathway to another. Published literature provide comprehensive information on the response of plants to drought and the role of hormones in regulating the response to drought from experiments directly imposing drought stress (dehydration stress-withholding water) or osmotic stress (turgor loss due to extracellular solutes) and experiments with mutants and others involving the functions of hormones and other signals. Changes in gene expression induced by drought overlap with gene expression regulated by hormones. This chapter presents the signal transduction pathways of hormones under drought stress and how they cross talk with each other in regulating the drought stress response in plants.