Evaluation of Drought-Tolerance Strategies in Cotton

Research made possible through the use of the wealth of genomic information and genetic resources available for model plant species such as Arabidopsis thaliana has led to a substantial increase in our knowledge about how plants respond to stressful environmental conditions. This leap in understanding provides the basis for many new strategies for optimization of stress tolerance in crop plants through both traditional and transgenic approaches. Although, to date, most of these strategies have been tested only in model plants, evaluation of some of them in important crop species, including cotton, is now underway. Application of novel stress-tolerance technologies will require extensive physiological and agronomic evaluation of plants that express these genes to determine their ultimate applicability to crop systems. A broad-based evaluation strategy for candidate genes will be necessary to test their value under a wide variety of field conditions. In cotton, this will include testing the effects of candidate genes on germination, seedling survival and stand establishment, vegetative growth and the transition to flowering, flowering period, boll maturation, and fiber development and quality. Though experiments in model species are valuable, experience shows that they do not guarantee similar results in a heterologous crop species. Our preliminary work with transgenic cotton plants that express transcription factors, such as ABF3 and CBF3, show that optimization of expression patterns using different promoters or other regulatory strategies will be necessary. The recent identification of complex post-transcriptional and post-translational regulatory mechanisms for stress-responsive gene expression reinforces the need for direct testing of new technologies in crop species. These mechanisms are able to fine-tune the expression of stress-responsive genes by ensuring their suppression under non-stressful conditions and attenuating stress responses in the face of prolonged stress exposure. However, since these mechanisms can be sequence-specific, we anticipate that, in some cases, different Evaluation of Drought-Tolerance Strategies in Cotton