Wound-inducible hybrid Bt protein SN19 confers pest control and resistance delay through localized expression in...

Maize (Zea mays L.) is a major global crop but suffers severe yield losses from lepidopteran and coleopteran pests such as Ostrinia nubilalis and Tanymecus dilaticollis. Constitutive expression of Bacillus thuringiensis (Bt) toxins in current transgenic varieties increases selection pressure for resistance and may raise biosafety concerns. To achieve effective yet spatially confined pest control, we developed transgenic maize expressing a hybrid Bt protein, SN19-comprising domains I and III from Cry1Ba and domain II from Cry1Ia-under the wound-inducible Asparagus officinalis PR1 (AoPR1) promoter.

PCR and reverse-transcription (RT)-PCR confirmed successful transformation and promoter-specific expression of the maize-codon-optimized SN19 (mcSN19) gene. Under the constitutive CaMV35S promoter, SN19 transcripts were detected in all tissues, including kernels, whereas the AoPR1 promoter restricted expression to wounded leaves and stems, remaining inactive in kernels. Quantitative (q)RT-PCR (Ct > 35) and blotting analyses verified strong induction at 18-72 h postwounding but no basal activity in unwounded tissue. Insect bioassays with O. nubilalis larvae showed complete mortality and pronounced feeding deterrence on AoPR1-SN19 leaves, whereas larvae survived on non-transgenic controls. These findings confirm effective wound-dependent SN19 expression conferring strong protection without constitutive exposure.

Localized induction of the hybrid Bt protein SN19 through the AoPR1 promoter offers an efficient strategy for maize protection that minimizes Bt accumulation in edible tissues, reduces metabolic load and may delay resistance evolution. This inducible platform provides a promising tool for sustainable pest management and can be extended to other crops and hybrid pesticidal genes. © 2025 Society of Chemical Industry.