Transgenic approaches to increase dehydration-stress tolerance in plants

Plant productivity is strongly influenced by abiotic stress conditions indu ced by drought, high salt and low temperature. Plants respond to these cond itions with an array of biochemical and physiological adaptations, at least some of which are the result of changes in gene expression. Transgenic app roaches offer a powerful means of gaining valuable information to better un derstand the mechanisms governing stress tolerance. They also offer new opp ortunities to improve dehydration-stress tolerance in crops by incorporatin g a gene involved in stress protection into species that lack them. In this review, we discuss progress made towards understanding the molecular eleme nts involved in dehydration-stress responses that have been used to improve salt or drought tolerance following several transgenic approaches. Further , we discuss various strategies being used to produce transgenic plants wit h increased tolerance to dehydration stress. These include the overproducti on of enzymes responsible for biosynthesis of osmolytes, late-embryogenesis -abundant proteins and detoxification enzymes. At this time, there is a nee d for a careful appraisal of the genes to be selected and promoter elements to be used, because constitutive expression of these genes may not be desi rable in all applications. In this context, the advantages and limitations of transgenic approaches currently being used are discussed together with t he importance of using stress-inducible promoters and the introduction of m ultiple genes for the improvement of dehydration-stress tolerance.