Transgenic plants over-expressing glutathione biosynthetic genes and abiotic stress tolerance

Abstract

Plants cannot survive without glutathione, or a functionally homologous thiol, as glutathione has diverse functions in plant growth and development, many of which cannot be performed by other thiols or antioxidants. The roles of glutathione in plants include the regulation of redox homeostasis, cell signaling and gene expression, and essential roles in key physiological and metabolic processes such as photosynthesis and sulfur assimilation. The cellular pool of reduced glutathione (GSH) can be depleted by oxidation of GSH to glutathione disulfide (GSSG), by reactive oxygen species (ROS), or by reacting with methylglyoxal (MG). The generation of ROS and MG increases in plant cells under abiotic stress, e.g., in plants exposed to heavy metals, salinity, drought, high or low temperatures, herbicides, or air pollutants. There is considerable evidence to suggest that enhanced activities of GSH utilizing and regenerating enzymes are crucial for abiotic stress tolerance in both model and cultivated plant species. Recently, the use of transgenic plants has clearly demonstrated the importance of GSH for stress tolerance, with plants over-expressing GSH biosynthetic genes and genes associated with maintaining GSH levels having increased GSH levels and showing improved tolerance to individual stressors. In addition, modulating the activities of GSH-related enzymes has also been shown to be important for multiple stress tolerance; however, many of the details of the roles GSH plays in multiple stress tolerance are still unresolved. The aim of this chapter is to provide a comprehensive overview of the diverse roles of GSH biosynthetic genes in improving abiotic stress tolerance by critically evaluating the research conducted using transgenic plants, expressing GSH-associated genes, grown under abiotic stress.