Drought Tolerance Enhancement with Co-Overexpression of DREB2A and APX in Indica Rice (Oryza sativa L.)

Rice is a major cereal crop providing food\r\nand energy to more than half of world’s population and drought is a challenging\r\nabiotic stress limiting rice production. Engineering drought tolerance trait is a major\r\nbottle neck because of multigenic control and complex nature. Two promising\r\ncandidate genes utilized in engineering drought tolerance include DREB2A\r\ntranscription factor (a master regulator of downstream stress inducible genes)\r\nand APX (an important ROS scavenging enzyme). Overexpression of DREB genes has shown encouraging results\r\nbut with a negative impact on plant morphology and production. Moreover,\r\nco-expression of DREB2A and APX genes’ influence on drought stress has not been studied. Hence, in the present\r\nstudy, overexpression of single genes DREB2A or APX and co-expression of these genes\r\nwere studied for enhancement of drought tolerance in indica rice. Both genes\r\nunder control of CaMV 35S promoter were transferred by Agrobacterium transformation into rice variety BPT5204 popular for\r\nslender grains in South India. Confirmation of T-DNA integration into rice\r\ngenome was done with PCR analysis of transgenes. Homozygous transgenic lines of\r\nDREB2A, APX and DREB2A-APX generated in T3 generation were evaluated for drought tolerance during seed germination,\r\nvegetative and reproductive stages. In seed germination stage, transgenic lines\r\nexhibited higher germination rates on 200 mM mannitol MS medium in comparison to WT. In vegetative stage,\r\nwith-holding water for 7 days transgenic lines exhibited higher chlorophyll,\r\nproline, reducing sugars and enhanced activities of APX, SOD and catalase\r\nenzymes as well as reduced MDA content. The qRT-PCR analysis revealed higher\r\nrelative transgene expression under drought stress. In reproductive stage,\r\nbefore maturity with-holding water for 7 days and restoring normal conditions, transgenic lines\r\ndeveloped longer panicles and a higher number of grains/plant\r\ncompared to WT. The overall results indicate that co-expression of\r\nDREB2A and APX can provide enhanced drought tolerance in rice plants to combat\r\nclimate change conditions.