Abstract
Rice is a major cereal crop providing food and energy to more than half of world’s population and drought is a challenging abiotic stress limiting rice production. Engineering drought tolerance trait is a major bottle neck because of multigenic control and complex nature. Two promising candidate genes utilized in engineering drought tolerance include DREB2A transcription factor (a master regulator of downstream stress inducible genes) and APX (an important ROS scavenging enzyme). Overexpression of DREB genes has shown encouraging results but with a negative impact on plant morphology and production. Moreover, co-expression of DREB2A and APX genes’ influence on drought stress has not been studied. Hence, in the present study, overexpression of single genes DREB2A or APX and co-expression of these genes were studied for enhancement of drought tolerance in indica rice. Both genes under control of CaMV 35S promoter were transferred by Agrobacterium transformation into rice variety BPT5204 popular for slender grains in South India. Confirmation of T-DNA integration into rice genome was done with PCR analysis of transgenes. Homozygous transgenic lines of DREB2A, APX and DREB2A-APX generated in T3 generation were evaluated for drought tolerance during seed germination, vegetative and reproductive stages. In seed germination stage, transgenic lines exhibited higher germination rates on 200 mM mannitol MS medium in comparison to WT. In vegetative stage, with-holding water for 7 days transgenic lines exhibited higher chlorophyll, proline, reducing sugars and enhanced activities of APX, SOD and catalase enzymes as well as reduced MDA content. The qRT-PCR analysis revealed higher relative transgene expression under drought stress. In reproductive stage, before maturity with-holding water for 7 days and restoring normal conditions, transgenic lines developed longer panicles and a higher number of grains/plant compared to WT. The overall results indicate that co-expression of DREB2A and APX can provide enhanced drought tolerance in rice plants to combat climate change conditions.
Highlights
Different abiotic environmental stresses have been responsible for limiting the conditions for plant exploitation and productivity worldwide
Key genes identified in various pathways expressed under drought stress include different transcription factors: viz., DRE-binding protein (DREB)/C-repeat-binding factor (CBF), ABA-binding factor (ABF), MYC, MYB [10] [11], ABA-responsive element (ABRE) and dehydration responsive element [12]
Generation of Transgenic Lines The DREB2A, ascorbate peroxidase (APX) and DREB2A-APX cassettes (Figures 1(A)-(C)) in pCAMBIA1300 vectors were mobilized into Agrobacterium (LBA4404) by freeze thaw method, independently
Summary
Different abiotic environmental stresses have been responsible for limiting the conditions for plant exploitation and productivity worldwide. Drought stress is one of the most adverse factors and considered as a severe threat to growth and productivity of sustainable crops [3]. In response to drought stress, plants induce the expression of different functional and regulatory genes [9]. Plants scavenge the reactive oxygen species (ROS) with antioxidative defense system to protect the cells from oxidative injury under drought stress conditions. Various ROS free radicals such as hydroxyl radical, hydrogen peroxide, superoxide and singlet oxygen are produced and accumulation of ROS during drought stress enhances lipid peroxidation and protein oxidation resulting in severe damage to plant cells [13] [14]
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