Candidate Genes for Drought Stress Tolerance in Cotton.

Among the many factors that limit world-wide crop productivity, unfavorable environmental conditions caused by abiotic factors such and drought and extreme temperatures are the most critical. Human population growth and the resulting increased need for agricultural products, loss of arable land and water resources, and climatic instability will limit our ability to meet these needs. One part of the solution to this problem will be to adopt new crop varieties that are able to maintain high productivity under suboptimal environmental conditions. Improvements will continue to be made through breeding but it is likely that transgenic approaches will also be necessary for agricultural productivity to keep pace with demand. These strategies require thorough knowledge of the molecular mechanisms used by plants to acclimate to harsh environmental conditions that comes through basic research in model plant species such as Arabidopsis, followed by application of these results to crop plants. While many genes are involved in abiotic stress responses, the ABA-responsive element binding factors (ABFs) and C-repeat binding factors (CBFs) are of particular interest as they play important roles in drought and thermal tolerance and have been shown to interact to coordinate responses to these stresses. Heterologous expression of the Arabidopsis ABF3 and CBF3 in cotton leads to increased drought tolerance, though with negative reproductive consequences. Characterization of ABF and CBF orthologs from cotton is underway and the effects of heterologous expression of these genes in Arabidopsis is being examined. We hypothesize that ectopic expression of endogenous ABFs and CBFs in cotton could confer increased abiotic stress tolerance while minimizing the negative effects. Thus, our results indicate that altered expression of genes that encode protein factors involved in the regulation of stress acclimation pathways shows promise but fine tuning of these methods and thorough testing of the physiological and agronomic impacts of these strategies will be required in order to determine their efficacy.