Can the Quest for Drought Tolerant Crops Avoid Arabidopsis Any Longer

The use of Arabidopsis as a model system in plant research has been a powerful tool for biologists in the last twenty years, yet crop scientists largely have considered Arabidopsis an unsuitable system for addressing agricultural problems. The realization that Arabidopsis genes can function ectopically in other plant species, together with recent advances in our understanding of Arabidopsis gene function, have greatly facilitated the potential for genetic manipulation of crop species. Based on the available data on function in Arabidopsis and on our current knowledge of phenological, morphological, and biochemical factors affecting water stress tolerance in plants, we identify in this chapter possible strategies to improve drought stress tolerance, using the powerful genetic model Arabidopsis. Specifically, we consider those Arabidopsis genes and mutants, whose respective functions and phenotypes may be directly or indirectly involved in improving drought stress tolerance. Genes that shorten or delay the flowering time, for instance, have been cloned and can be used to ehance mechanisms such as drought escape and avoidance. Similarly, genes that alter stomatal function, leaf shape, area, and other aspects of plant morphology such as leaf architecture, may be good candidates to design a more efficient phenotype in terms of water consumption. This objective may also be accomplished by transferring traits such as hairiness and waxiness of the leaf surface, which are known xerophytic adaptations that have been characterized in Arabidopsis. In addition to their regulation of water loss, plants may avoid drought stress by enhancing the capacity to take up water from the soil. Mutants with altered root morphology and architecture have been described and are excellent candidates for elucidating the complex coordination between water uptake and loss in plants. These include mutants with altered root hydraulic conductivity, variable diameter of vessels and amount of vasculature within the root or stem. Finally, considering the difficulties underlying the possible improvement of plant water-use efficiency (WUE), we identify alternative strategies to improve yield in water-limiting environments by manipulating the harvest index (HI).