The expression of five genes involved in photosynthesis was investigated under different salinity conditions in Dunaliella salina. These genes encodes ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) large and small subunits, major light-harvesting chlorophyll (chl) a/b protein of photosystem II, carbonic anhydrase and adenosine tri phosphate synthase alpha subunit. As D. salina grows in hypersaline conditions, it is important to study expression of these genes in relation to different salinity levels. Changes in the mRNA level under different NaCl conditions were determined using the comparative CT method. Cell number and chl a content were estimated to determine optimal growth at different NaCl concentrations. Real-time PCR results showed enhanced expression of photosynthesis genes upon exposure of D. salina cells from Sambhar Lake to 1.7 M NaCl containing medium. This salinity corresponds to only one-third of the salinity of the Sambhar Lake habitat. In another salt condition, the expression level of all genes was found to be down-regulated at 1.0 M (sub-optimal concentration for growth of D. salina), 2.5 M and 3.0 M NaCl (supra-optimal concentration for growth) when compared with 1.7 M NaCl containing medium as a control. The present study will help in understanding the salinity tolerance in D. salina as a model microalga.
Key words: Dunaliella . Photosynthesis . NCBI primer designing tool . real-time PCR