Novel codon-optimized cry1Ac34 gene from Indian Bt isolate confers resistance against Helicoverpa armigera in...

The increasing resistance of Helicoverpa armigera to currently deployed Bacillus thuringiensis (Bt) genes in transgenic crops necessitates the development of new insecticidal genes that can effectively control this pest. This study evaluates the in-planta efficacy of cry1Ac34, a truncated, plant codon-optimized gene derived from an Indian Bt isolate (SK-783). The cry1Ac34 gene was successfully introduced into Nicotiana tabacum through Agrobacterium-mediated transformation. Following the transformation, PCR-positive T₀ transgenic plants expressing the Cry1Ac34 protein were identified. Subsequent analyses of T₁ progeny lines, using Southern blotting and qRT-PCR, confirmed the stable integration and expression of the gene. Insect bioassays conducted with detached leaves from transgenic lines demonstrated impressive mortality rates of up to 95% in line C12 of T₁ against first larval instars of H. armigera. Protein expression levels in T₁ transgenic plants ranged from 0.86 µg/g to 1.36 µg/g fresh leaf weight. Additionally, the study observed significant sub-lethal effects, including reduced weight gain and larval growth, delays in pupation, and pre-pupal death. Histopathological analysis revealed disintegration of brush border membranes in the midguts of fourth instar larvae that had been fed transgenic leaves. The successful expression and efficacy of the codon-optimized cry1Ac34 gene highlight its potential as a viable solution for controlling H. armigera. This research suggests cry1Ac34 as a promising candidate for deployment in the development of new insect-resistant transgenic crops, which may help combat the escalating resistance challenges currently faced in agricultural pest management.