Improvement of Drought Resistance through Manipulation of the Gibberellic Acid Pathway

Drought is a severe issue facing agriculture due to global climate change and the lack of rainfall in some areas. In recent years, nearly the entire state of California experienced extremely dry conditions, which greatly impacted on crop productions. Therefore, increasing plants' ability to survive under drought is of great importance to agricultural industry including horticulture. Plant hormone Gibberellic acid (GA) mediates diverse aspects of plant growth and development including seed germination, stem elongation, leaf expansion, and flower and seed development. An Arabidopsis gibberellin acid insensitive mutant gai-1 has been shown to reduce plant height and alter GA response, resulting in an undesirable dwarf phenotype but enhanced drought resistance.  Overexpression of the gai using the 35S promoter would result in strong drought resistant, but completely dwarf plants. To overcome these adverse effects, we propose to use inducible promoters to drive the expression of the gai-1 gene. This strategy will allow us to initiate expression of the gai-1 at specific times or under water stress conditions.  We hypothesize that temperately cell rest caused by over-expression of the gai-1 gene would lead to better drought resistance and improve crop productivity without an undesirable dwarf phenotype. We have generated eleven transgenic plants in which the gai-1 gene was over-expressed under a stress-inducible promoter. These plants were subjected to drought treatment and initial characterizations are under way.