Abstract
Water deficit is a consequence of several different stresses including drought, salinity and extreme temperatures. It severely limits plant growth and productivity. Traditional plant breeding programmes have contributed significantly to the generation of stress-tolerant plants, but the process is rather time-consuming, expensive and hampered by the multigenic nature of the stress. Techniques developed in the field of plant molecular biology have the potential to modify plants for growth under unfavourable conditions and to provide new genotypes faster than traditional breeding is able to. The engineering of metabolic pathways associated with drought stress has emerged as a promising way to improve tolerance in model and crop plants. In recent years, efforts in this area have led to improvements in drought stress tolerance. Attempts to engineer improved drought tolerance using single- or multi-gene transfer of candidate genes offer rapid improvements in drought tolerance, although such genetic engineering strategies are limited by an incomplete understanding of stress tolerance mechanisms. Major efforts are required in molecular dissection of drought tolerance mechanisms in important crop plants. This review summarizes recent advances in elucidating stress response mechanisms and their biotechnological applications. Emphasis is placed on transgenic plants that exhibit improved drought tolerance. Various strategies to obtain drought-tolerant plants will be described and discussed.