Abstract: Transposable elements (TEs) are abundant and evolutionarily important components of plant genomes, yet the population-scale landscape of TE insertion polymorphisms (TIPs) and their regulatory roles in gene expression and trait variation remain insufficiently understood. In this study, genomic resequencing, RNA-seq, and agronomic trait data from a panel of 381 Brassica napus accessions were integrated to characterize population-level TIP dynamics and assess their impacts on gene regulation, ecotype differentiation, and phenotypic innovation. Using a developed computational pipeline, a robust pan-TE library was constructed based on 28 diverse reference genomes, and 77,603 TIP loci were profiled by mapping resequencing data from 381 accessions. Most TE insertions were found to be dispensable and weakly linked to neighboring SNPs, suggesting that they represent recent or ecotype-specific variants that serve as independent sources of regulatory and adaptive diversity in B. napus. The regulatory roles of TEs were examined through two complementary strategies (direct-effect analyses and TIP-based eQTL mapping), which together revealed that TEs modulate gene expression via both cis- and long-range trans-effects. Notably, TE-mediated trans-regulation, rarely investigated in previous studies, was found to be widespread, with trans-effects predominating and displaying strong tissue specificity, emphasizing the extensive regulatory influence of TEs on the plant transcriptome. Furthermore, selective sweep analyses identified ecotype-specific TIPs associated with adaptive divergence, particularly those contributing to semi-winter type diversification. TIP-based genome-wide association studies (GWAS) revealed 1,102 candidate insertions significantly associated with key agronomic traits, including flowering time, fatty acid composition, and glucosinolate content, some of which were not detected by SNP-based analyses. This study provides the population-scale atlas of TE insertions in B. napus, uncovers their extensive regulatory roles, and demonstrates their contribution to adaptation and trait variation, offering valuable resources for breeding and functional genomics.

Key words: Brassica napus, ecotype divergence, gene expression regulation, phenotypic variation, transposable insertion polymorphism