Crosstalk between Salt, Drought, and Cold Stress in Plants: Toward Genetic Engineering for Stress Tolerance

Salinity, drought, and low temperature are the major abiotic stresses that limit plant growth and productivity. The perception of the abiotic stresses and signal transduction to switch on adaptive responses are critical steps in determining the survival and reproduction of plants exposed to adverse environments. Plants have stress-specific adaptive responses as well as responses that protect them from more than one environmental stress. Understanding the mechanisms by which plants perceive and transduce the stress signals to initiate adaptive responses is essential for engineering stress-tolerant crop plants. Molecular and genomic studies have shown that several genes with various functions are induced by salinity, drought, and cold stresses, and that various transcription factors are involved in the regulation of stress-inducible genes. Genetic engineering strategies rely on the transfer of one or several genes that are involved in signaling and regulatory pathways, encoding enzymes present in pathways leading to the synthesis of functional and structural protectants, or encoding stress-tolerance-conferring proteins. Molecular control mechanisms for abiotic stress tolerance are based on the activation and regulation of specific stress-related genes. These genes are involved in the whole sequence of stress responses, such as signaling, transcriptional control, protection of membranes and proteins, and scavenging of free radicals and toxic compounds. The products of stress-inducible genes function not only in stress tolerance but also in stress response. There are multiple stress perception and signaling pathways, some of which are specific, but others may crosstalk at various steps. Recently, progress has been made in identifying components of signaling pathways involved in salt, drought, and cold stresses. This chapter highlights the involvement of both abscisic acid (ABA)-dependent and ABA-independent signaling components and their interaction or convergence in activating the stress genes. We restrict our discussion to salinity, drought, and cold stress, with emphasis on strategies for engineering plants for salt tolerance.