Genetic manipulation of plants for increased drought tolerance

On a world basis, water availability is considered the main constraint for crop production. Concerns about water accessibility have always accompanied crop production in dry areas, which are on the other hand the most extensive areas for agriculture on the earth. As a consequence, men had to develop agricultural strategies to cope with water shortage, growing the plants during the short climatic interval of water availability and selecting plants possessing a relatively superior tolerance to water deficiency. Although development of drought tolerant plants by conventional breeding methods has resulted in modest Correspondence/Reprint request: Dr. Gerardo Armando Aguado-Santacruz, Plant Biotechnology Unit, National Institute for Forestry, Agriculture and Livestock Research, Campo Experimental Bajío –INIFAP, Km 6.5 Carretera Celaya-San Miguel de Allende, Celaya, Gto. 38010, México. E-mail: [email protected] Gerardo Armando Aguado-Santacruz 72 achievements, it is expected that genetic transformation contribute to widen still more the water stress tolerance range of plants. A great detail is currently known on the physiology and molecular biology of plants subjected to water stress, from the perception of the stimulus to the response module responsible for reducing the detrimental effects of water deprivation. Part of this deep understanding about the molecular basis of the plant response to water stress has been derived from other model organisms, such as yeast, and it is now being landed into practical grounds to modify the genome of plants for increasing their water stress tolerance. From the existing experimental evidence several conclusions can be drawn. First, there is enormous and complex information concerning the transduction pathways and molecular responses of plants to water deficit, but less is known about the receptors sensing suboptimal osmotic conditions in plants. Second, practically all genetic modifications tested up to now, from the initial perception steps to the final response module, have resulted in an improved response of plants to water stress, with osmolyte pathway alteration being the most studied approach. Third, if a logical scientific framework is to be developed, it is evident the urgency for testing the physiological and productive performance of the genetically modified crops under field conditions in order to define the most robust approach to be adopted in future work. Several issues remain to be addressed in upcoming research: Should we introduce or modify a single pleiotropic gene localized upstream the response module? or Should we alter a gene or set of genes with more defined functions at the response module level? Is a multigenic approach, altering genes at the perception, transduction and/or response module, a more robust strategy for increasing drought tolerance? Can the chloroplast transformation technology assist in improving the effect of the genes already established as conferring water stress tolerance?