# Comparative Analysis of Insect Resistance in Transgenic Populus × euramericana cv. Neva Expressing Dual Bt Genes from Different Sources

## TL;DR

This study compares insect resistance in genetically modified poplar trees with different Bt gene configurations, showing that dual-gene lines offer broader pest resistance than single-gene lines.

## Contribution

The study introduces and evaluates dual Bt gene configurations in poplar trees, revealing broader pest resistance and molecular responses in insect pests.

## Key findings

- Dual-gene poplar lines showed broader resistance to both lepidopteran and coleopteran pests compared to single-gene lines.
- Single-gene line pb9 achieved 100% mortality against Hyphantria cunea but lacked broad resistance.
- Transcriptomic analysis revealed molecular changes in insect pests, including developmental delays and altered gene expression.

## Abstract

This study systematically evaluated insect resistance in transgenic poplar lines carrying three distinct Bacillus thuringiensis (Bt) gene vector architectures: a single-gene pb vector (Cry1Ac), a reverse-oriented double-gene n19 vector (Cry1Ac-Cry3A), and a forward-oriented double-gene n5 vector (Cry3A-Cry1Ac). The transgenic lines were accordingly designated as pb8/pb9, n19a/n19b, and DB7/DB16, respectively. Molecular analyses confirmed stable Bt gene integration, with the expression of Cry3A being consistently higher than that of Cry1Ac expression. Bioassays showed that dual-gene lines conferred broader insect resistance to pests than that of single-gene lines against both lepidopteran (Hyphantria cunea) and coleopteran (Plagiodera versicolora, Anoplophora glabripennis) pests. In contrast, the single-gene line pb9 exhibited specialized, high efficacy against H. cunea, achieving 100% mortality. Transcriptomic analysis of P. versicolora larvae fed the double-gene high-resistance n19a line and low-resistance DB16 line revealed multi-level molecular responses to Bt stress, including up-regulation of toxin-activating proteases, altered receptor expression, and suppression of growth-related genes. These changes were associated with significant developmental delay (8.33–20.83% reduction in the molting index). Our findings characterize the insect resistance and molecular profiles of the six transgenic poplar lines, as follows: multi-gene lines (n19a/n19b and DB7/DB16) confer broad-spectrum pest resistance, whereas single-gene lines (pb8/pb9) exhibit targeted efficacy. These results support the utility of these lines for pest-specific poplar breeding programs.