Background: A number of strategies are being followed to enhance the tolerance of maize and wheat to water-stress conditions, including the development of genetically-engineered varieties containing various gene constructs believed to enhance the performance of these varieties under stress conditions. While there are a number of issues that must be addressed if such transgenic varieties are to be effectively deployed to farmers (e.g., intellectual property, biosafety, food/feed/environmental safety), if genetic systems based on transgenes can be found effective, they will provide an attractive and complementary option for improving a plant’s performance under stress conditions. Particularly attractive is the single, dominant nature of the transgene that makes the transfer and maintenance of this system in any variety much easier than those based on multiple, quantitative genetics.

Molecular mechanisms of water stress response have been investigated primarily in the model plant species Arabidopsis thaliana. Analyses of the expression of dehydration-inducible genes have shown that at least four independent signaling pathways function in the induction of stress-inducible genes in response to dehydration: two are ABA-dependent and two are ABA-independent. Several stress-induced genes, such as rd29A in A. thaliana, are induced through the ABA-independent pathway. The Dehydration-Responsive Element Binding gene 1 (DREB1) and DREB2 are transcription factors that bind to the promoter of genes such as rd29A, thereby inducing expression in response to drought, salt, and cold.

DREB1A has been over expressed in transgenic Arabidopsis plants, and the resulting phenotype showed a strong induction of the expression of the target genes under unstressed conditions but also caused dwarfed phenotypes in the transgenic plants. These transgenic plants also revealed freezing and dehydration tolerance. In contrast, over expression of the DREB2A induced weak expression of the target genes under unstressed conditions and caused growth retardation of the transgenic plants. The stress-regulated expression of DREB1A gene by the rd29A promoter produced plants with increased tolerance to freezing, salt, and drought stresses without a drastic change in the normal phenotype of the transformed plants. As part of CIMMYT’s efforts to enhance drought tolerance in wheat, the A. thaliana DREB1A gene under control of a stress inducible promoter from the rd29A gene was obtained from Dr. Shinozaki, JIRCAS for testing initially in wheat and then in maize.

Objectives:

1. Transform the super-transformable wheat variety with the rd29A::DREB1A gene construct
2. Select the best events under water stress conditions in the biosafety greenhouse
3. Evaluate the best events under field conditions to confirm the increased tolerance to water-stress conditions and the lack of negative effects under full irrigation

Target Germplasm: MPB Bobwhite-26

Gene(s): rd29A::AtDREB1A

Partner(s): Japanese International Research Center for Agricultural Sciences (JIRCAS)

Status: Several hundred events have been produced and screened under water-stress conditions in the biosafety greenhouse. The events demonstrating the best level of tolerance to water-stress were confirmed to contain the DREB gene and are being evaluated under field conditions in the screenhouse at CIMMYT, El Batan, Mexico. Further field trials will be conducted if the transgenics demonstrate enhanced performance under water-stressed conditions.

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