Analysis of DNA Polymerase λ Activity and Gene Expression in Response to Salt and Drought Stress in Oryza sativa Indica Rice Cultivars

The plants are constantly subjected to varying degree of environmental stress. These stresses results in severe damage to the DNA of the plants, which if not repaired can lead to the impairment of their genetic material, and can prove fatal for the plants. The present work studies the damage to the genomic DNA in response to salinity and drought stress on the indica rice cultivars. The comet assay results showed that maximum DNA damage was seen in the IR29 cultivar, whereas, the Nonabokra cultivar showed minimal DNA damage. The gene expression profiling of DNA polymerase lambda (OsPol lambda), the only X family DNA polymerase in rice which is involved in the repair of DNA damage, shows that the gene is up-regulated in all the rice cultivars irrespective of their degree of tolerance to the environmental stresses. Further the enzymatic activity of the OsPol lambda protein was studied in the three rice cultivars and it was revealed that the OsPol lambda activity increases in response to stresses in all the rice cultivars, however, the salinity-susceptible IR29 showed a more prominent increases in the activity of OsPol lambda than Nonabokra (salinity tolerant) and N22 (drought tolerant) cultivars. The study on the upstream regions of the OsPol lambda gene to identify the different cis acting upstream elements effecting the gene expression showed the presence of unique stress responsive regulatory elements was detected in the upstream region of OsPol lambda gene. The present study suggest that the OsPol lambda gene expression and enzymatic activity is enhanced in response to these abiotic stress, thus, playing an important role in the repair of salinity and drought induced DNA damages in indica rice cultivars.