Abstract
BackgroundBt-cry1Ac gene has been reputedly effective against Helicoverpa armigera a notorious lepidopteran pest. Reports on the expression of full-length and truncated cry1Ac genes in plants for effective resistance against Helicoverpa sp. have been documented however, their performance is still ambiguous. Moreover, the question remains to be addressed that truncation of 3′ end of the native gene was documented and suggested for active insecticidal toxin production while the most successful transgenic event(s) of commercialized-cotton are based on full-length of the cry gene. Therefore, we performed a comparative study on the efficacy of the two versions of cry1Ac genes (full-length: 3,510 bp and truncated: 1,845 bp) in T0 and T1 transgenic tomato plants and analyzed the extent of protection against H. armigera and also compared the results with our previous findings related to a successful transgenic tomato line Ab25E, expressing cry1Ab gene. The integration of cry1Ac gene(s) in T0 transgenic plants and its inheritance in T1 progeny was observed by PCR, RT-PCR and Southern blot hybridization analysis while, the toxin integrity, expression and toxicity was monitored by Western immunoassay, DAS-ELISA and insect bioassay respectively.ResultsAn average transformation frequency and Bt-Cry protein content of 16.93 ± 2.10 and 0.0020–0.0128% of total soluble protein (TSP) was obtained with pRD400 vector (Trcry1Ac) while, a much lower value of 9.30 ± 2.041 and 0.0001 ― 0.0026% of TSP was observed with pNBRI-1 vector (Flcry1Ac), respectively. The promising Trcry1Ac T0 transgenic plants and their T1 progeny gave full protection from H. armigera. Although Flcry1Ac gene showed lower transformation frequency and lower expression, it showed higher toxicity to H. armigera when compared with truncated Trcry1Ac gene.ConclusionsThe full-length cry1Ac gene can be redesigned for higher expression and performance in dicots or a hybrid gene could be designed having a blend of strong receptor binding and stable expression characteristics for enhanced efficacy and toxicity to the susceptible insects.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-015-0991-x) contains supplementary material, which is available to authorized users.
Highlights
Bacillus thuringiensis (Bt)-cry1Ac gene has been reputedly effective against Helicoverpa armigera a notorious lepidopteran pest
Development of transgenic tomato plants Agrobacterium-mediated tomato transformation was performed with vector constructs (Figure 1A and B) pRD400 harbouring truncated cry1Ac gene (Trcry1Ac) and pNBRI–1 harbouring full-length cry1Ac gene (Flcry1Ac) using the modified procedure
Our results obtained from Polymerase chain reaction (PCR), Southern blotting and RT-PCR analyses of transgenic tomato plants have confirmed the stable integration of Trcry1Ac and Flcry1Ac genes in T0 plants and their respective T1 progeny
Summary
Bt-cry1Ac gene has been reputedly effective against Helicoverpa armigera a notorious lepidopteran pest. Reports on the expression of full-length and truncated cry1Ac genes in plants for effective resistance against Helicoverpa sp. We performed a comparative study on the efficacy of the two versions of cry1Ac genes (full-length: 3,510 bp and truncated: 1,845 bp) in T0 and T1 transgenic tomato plants and analyzed the extent of protection against H. armigera and compared the results with our previous findings related to a successful transgenic tomato line Ab25E, expressing cry1Ab gene. Koul et al SpringerPlus (2015) 4:203 insecticidal δ-endotoxins specific to different group of insects (Schnepf et al 1998) These toxins are highly specific to the target insects, non-toxic to animals and human beings, non-hazardous and eco-friendly (Schnepf et al 1998; Gatehouse 2008). The mode of action of Cry1Ac toxin can be best explained by the ‘Jurat-Fuentes model’ which suggests that cytotoxicity is due to the synergistic effect of osmotic lysis and cell signaling process, and involves the features of both the ‘Bravo model’ and the ‘Zhang model’ of toxin mode of action (Jurat-Fuentes and Adang 2006; Pardo Lopez et al 2013)
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