Genetic engineering of indica rice with AtDREB1A gene for enhanced abiotic stress tolerance

Drought and cold stresses are major abiotic stresses that affect rice productivity. Therefore, enhancing tolerance to these stresses is necessary for sustaining rice productivity. Overexpression of the AtDREB1A gene has been shown to confer tolerance to both drought and cold stresses in diverse plant species. Hence, we genetically engineered indica rice cv. Pusa Sugandh 2 with AtDREB1A gene under the transcriptional control of stress responsive AtRD29A promoter. The transformants were confirmed for the stable integration of transgene in the rice genome by using PCR, RT-PCR and Southern blot analyses. Two single copy transgenic events (T3) and non-transgenic (NT) plants grown in pots were subjected to drought and cold stresses for 14 days. Transgenic plants exhibited enhanced tolerance to both drought and cold stresses as compared with NT plants. Transgenic plants maintained significantly higher leaf relative water content (LRWC), chlorophyll content, total sugars and proteins, but lower canopy temperature as compared with NT plants. Microarray analysis of AtDREB1A transgenic rice line (TL4) subjected to drought stress at reproductive stage led to the identification of 256 differentially expressed genes (DEGs), of which 201 were upregulated under drought stress. Interestingly, ~ 38% of the up-regulated genes coded proteins for chloroplast structure and function, which is a unique finding of this study. About 47% of the DEGs were enriched with CRT/DRE cis-regulatory elements in their promoters. Of these CRT/DRE cis-element containing genes, 50% genes coded for chloroplast function suggesting that these genes might be the direct targets of DREB1A TF. Up-regulation of TFs ZFP179 and NF-YC1, which are positive regulators of stress tolerance and downregulated TFs HOX22 and OsNAP, which are negative regulators of stress tolerance might have contributed to the enhanced drought tolerance of AtDREB1A transgenic plants. In addition, AtDREB1A-mediated orchestration of genes for chloroplast function appeared to have played an important role in not only providing carbon requirements of plants for survival and growth, but also helped minimize photo-inhibition and ROS accumulation in chloroplast under drought stress. Thus, stress-inducible overexpression of AtDREB1A in rice is a useful strategy to enhance drought and cold tolerance in the major staple food crop of the world.