Analyses of multicopy insertions and unintended responses to drought stress in dual Bt gene transgenic poplar

The integration and expression of foreign genes can produce unintended effects while bringing specific functions to plants. As the frequency and severity of droughts are increasing worldwide, it is of great significance to study the unintended effects of Bacillus thuringiensis ( Bt ) transgenic poplar for important tree species in the timber industry under drought stress for the application of transgenic trees. In this study, the dual Bt ( Cry1Ac, Cry3A ) gene transgenic Populus × euramericana cv. neva (poplar 107) line DB1 with high insect resistance and the wild type (WT) were used as the testing materials. Based on Nanopore sequencing, it was found that there were no major genomic structural variation and inserted by multiple copies in line DB1; Under different degrees of drought stress, the expression of adjacent genes was affected in different extents, and there was no correlation between toxic protein content and Bt gene expression; The growth and physiological data showed that under drought stress, the aggravated membrane damage, altered hormone content, and decreased peroxide scavenging ability of line DB1 may be the reasons for its weakened growth; The transcriptome data showed that under drought stress, Bt gene expression had a stronger effect on receptor gene expression, line DB1 responded to Bt gene expression through gene expression changes related to energy metabolism, hormone synthesis and signal transduction pathways, and abscisic acid played a critical role in line DB1 response to drought stress and Bt gene expression. This study provides unique insight into the safety evaluation, management and breeding of dual Bt gene transgenic poplar 107. • Multiple copies of T-DNA were found in transgenic line DB1. • There was no correlation between transcription and expression of foreign genes. • The growth of transgenic line DB1 was weaker than WT. • The impact of foreign gene expression on differential gene was greater. • Abscisic acid plays a crucial role in response to foreign genes.