Abstract
Recently, Bacillus thuringiensis (Bt) cry genes encoding insecticidal Cry proteins have been widely applied for the construction of transgenic crops resistant to insect pests. This study aimed to construct novel mutant cry1Ac genes for genetically modified crops with enhanced insecticidal activities. Using multi-site directed mutagenesis, 34 mutant cry1Ac genes were synthesized and converted at 24 amino acid residues, located on domain I (8 residues) and domain II (16 residues). These mutant genes were expressed as a fusion protein with polyhedrin using the baculovirus expression system. The expressed proteins were occluded into polyhedra and activated stably to 65kDa by trypsin. Among these, Mut-N04, N06 and N16 showed high levels of insecticidal activities against larvae of Plutella xylostella, Spodoptera exigua, and Ostrinia furnacalis. Mut-N16, which showed the highest insecticidal activity, is expected to be a desirable cry gene for introduction into transgenic crops. This study could provide useful means to construct mutant cry genes with improved insecticidal activities and expand host spectra for transgenic crops.
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