Ectopic expression of Xenorhabdus nematophila chitinase in tobacco confers resistance against Helicoverpa armigera

Chitinase plays a vital role in plant defense against insect pests and fungal pathogens due to its ability to hydrolyse chitin, which forms the major portion of the lining of gut membrane of insects and the cell wall of fungi. Earlier we reported a similar to 76 kDa chitinase protein isolated from Xenorhabdus nematophila strain (ATCC 19061). Purified chitinase protein was tested against the larvae of Helicoverpa armigera,a major crop pest and when fed orally to the larvae, it proved to be toxic. In the present study, we report the generation of transgenic tobacco plants expressing the chitinase gene of X. nematophila. The stable integration of the chitinase gene was confirmed by Southern blot while the expression of the gene was checked by RT-PCR analysis and quantification of chitinolytic activity. The transgenic lines were phenotypically normal and healthy. The result of bioassays revealed that the tobacco lines expressing increased level of chitinase protein showed 93-100% mortality of larvae of H. armigera when fed on the transgenic leaves expressing chitinase. A considerable reduction in leaf damage (55-76%) was also observed in transgenic lines as compared to the damage in untransformed control plants when the larvae were allowed to feed on the transgenic leaves. The larvae feeding on transgenic leaves showed adverse effect on their growth, development and survival. Thus we propose, the chitinase gene can prove to be a potent candidate for pest control in crop plants in future.