Antisense and RNAi expression for a chloroplastic superoxide dismutase gene in transgenic plants

The cDNA of tomato chloroplastic Cu/Zn-superoxide dismutase was used to construct transgenic tobacco (Nicotiana plumbaginifolia). It was found that the gene expression of Cu/Zn-superoxide dismutase can constitutively be reduced in the transgenic tobacco plants because of double-stranded (dsRNA) expressed in the form of intronspliced hairpin structures and antisense suppression. Furthermore, the endogenous chloroplastic Cu/Zn-superoxide dismutase gene in tobacco was established as a target for silencing due to the operation of hpRNA and antisense RNA constructs. However, under salt and PEG-induced stress, the cytosolic Cu/Zn-superoxide dismutase activity in transformed plants obviously increased. At the same time, the PEG pretreatment was able to promote tolerance of the transgenic plants to the salt stress. These results indicated that the use of hpRNA and anti-sense was able to successfully knockout the transcript encoding a chloroplast superoxidase dismutase. The null transformed plants grown under stress produced or retained other superoxide dismutase to compensate for the loss of the chloroplast. Consequently, hpRNA constructs would be helpful in discovering and validating the endogenous chloroplastic Cu/Zn-superoxide dismutase gene, and to prove the cytosolic alternative pathway of plant antioxidation associated with the function of Cu/Zn-superoxide dismutase gene under an unfavorable environment. Meanwhile, the experiment will provide an important technique for the antisensing strategies operating in tobacco.