2. Progress in functional and molecular genomics toward understanding stress perception

dissection of the genetic determinants associated with abiotic stress responses. Major breakthroughs included (1) development of molecular markers for gene mapping and the construction of associated maps, (2) the development of expressed sequence tags (ESTs) libraries, (3) the complete sequencing of Arabidopsis, maize and rice genomes, (4) the development of T-DNA tagged mutagenic populations of Arabidopsis and (5) the development of forward genetics tools such as Targeting Induced Local Lesions in genomes (TILLING) technique to assess functional

Figure 1. The process of plant response to abiotic stresses. The plant abiotic stress response pathway involves stress sensing, stress transduction and altered metabolism. Stress tolerance is achieved through expression of a large number of genes that accumulate stress-related transcription factors, chaperon function proteins, ROS scavenging enzymes, primary

Understanding Plant Responses to Drought and Salt Stresses: Advances and Challenges in "Omics" Approaches

http://dx.doi.org/10.5772/intechopen.81041

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Exploring genome sequences of Arabidopsis and rice and progress toward development of molecular markers and some new techniques has enabled positional cloning of mutated genes

3. Map-based cloning of abiotic stress-related genes

and secondary metabolites, osmoprotectants and cellular and vacuolar membrane antiporters.

analysis of genes [11].

Abiotic stress tolerance is a polygenic trait that involves the expression of many sets of genes working in different pathways [8]. Plants have a well-organized system of sensing the environmental signals and responding to them in the form of gene expression [9]. The process of stress perception is comprised of a set of events including stress signaling, stress transduction and gene expression that result in accumulation of transcription factors, stress-related proteins, enzymes and metabolites (Figure 1). In order to fully understand the plants abiotic stress tolerance, and to modify it with the help of transgenic technologies, understanding the process of stress perception at the molecular level is very important. The application of functional genomics technologies has added new dimensions to our understanding of plant responses to environmental stresses [10]. The progress of abiotic stress tolerance in plants through conventional breeding programs has met with limited success, mainly because of the polygenic nature of abiotic stress responses in plants. However, during the last decade, considerable progress was made toward development of functional genomic tools that allowed the functional Understanding Plant Responses to Drought and Salt Stresses: Advances and Challenges in "Omics" Approaches http://dx.doi.org/10.5772/intechopen.81041 77

important crop plants worldwide [1]. The resultant adverse changes in plant growth and productivity are orchestrated at the morphological, molecular and physiological levels [2]. The physiological effects of these stress conditions on plant developmental processes are mostly overlapping. Drought and salt stresses, in particular affect plants physiological and developmental processes by imposing osmotic and oxidative stresses. In addition, salt stress causes ionic stress and Na+ toxicity. These stress conditions, in turn, induce cellular damages resulting in the disruption of ionic and osmotic [3]. In response to these stress conditions, plants generate a set of events comprising perception and transduction of stress signals. These changes ultimately result into expression of stress-related genes that induces alterations in metabolic processes [3]. The abiotic stress responses are generally polygenic in nature and are

Being a polygenic trait, achieving abiotic stress tolerance in crop plants through conventional breeding is a tedious and time-consuming approach. In this respect, comparative genomics has been utilized to explore candidate genes conferring tolerance to salt, drought and extreme temperature stresses in several plants [5, 6]. In recent years, appreciable work has been conducted to identify abiotic stress-related transcriptomes and proteomes in several plant species. The availability of these information in plants have paved the way for dissecting abiotic stress responses at the molecular level that provided a base for transgenic approaches against abiotic stresses. These approaches were utilized to engineer several crop plants in order to enhance their abiotic stress tolerance [4, 7]. However, taking into consideration the polygenic nature of abiotic stress tolerance, detailed transcriptomic and proteomic studies are required across the plant species to fully dissect the stress-response pathway. Such information will add to the current efforts to find suitable genes for plant transformation against abiotic stresses. The current review summarizes the recent findings on abiotic stress tolerance-related transcriptomic and

2. Progress in functional and molecular genomics toward understanding

Abiotic stress tolerance is a polygenic trait that involves the expression of many sets of genes working in different pathways [8]. Plants have a well-organized system of sensing the environmental signals and responding to them in the form of gene expression [9]. The process of stress perception is comprised of a set of events including stress signaling, stress transduction and gene expression that result in accumulation of transcription factors, stress-related proteins, enzymes and metabolites (Figure 1). In order to fully understand the plants abiotic stress tolerance, and to modify it with the help of transgenic technologies, understanding the process of stress perception at the molecular level is very important. The application of functional genomics technologies has added new dimensions to our understanding of plant responses to environmental stresses [10]. The progress of abiotic stress tolerance in plants through conventional breeding programs has met with limited success, mainly because of the polygenic nature of abiotic stress responses in plants. However, during the last decade, considerable progress was made toward development of functional genomic tools that allowed the functional

shared in multiple abiotic stresses [4].

76 Transgenic Crops - Emerging Trends and Future Perspectives

proteomic studies in plant species.

stress perception

Figure 1. The process of plant response to abiotic stresses. The plant abiotic stress response pathway involves stress sensing, stress transduction and altered metabolism. Stress tolerance is achieved through expression of a large number of genes that accumulate stress-related transcription factors, chaperon function proteins, ROS scavenging enzymes, primary and secondary metabolites, osmoprotectants and cellular and vacuolar membrane antiporters.

dissection of the genetic determinants associated with abiotic stress responses. Major breakthroughs included (1) development of molecular markers for gene mapping and the construction of associated maps, (2) the development of expressed sequence tags (ESTs) libraries, (3) the complete sequencing of Arabidopsis, maize and rice genomes, (4) the development of T-DNA tagged mutagenic populations of Arabidopsis and (5) the development of forward genetics tools such as Targeting Induced Local Lesions in genomes (TILLING) technique to assess functional analysis of genes [11].
