Allopolyploid oilseed rape (Brassica napus) is an important oil crop and vegetable. However, the latest version of its reference genome, with collapsed duplications, gaps, and other issues, prevents comprehensive genomic analysis. Herein, we report a gap-free assembly of the rapeseed cv. Xiang5A genome using a combination of ONT (Oxford Nanopore Technologies) ultra-long reads, PacBio high-fidelity reads, and Hi-C datasets. It includes gap-free assemblies of all 19 chromosomes and telomere-to-telomere assemblies of eight chromosomes. Compared with previously published genomes of B. napus, our gap-free genome, with a contig N50 length of 50.70 Mb, has complete assemblies of 9 of 19 chromosomes without manual intervention, and greatly improves contiguity and completeness, thereby representing the highest quality genome assembly to date. Our results revealed that B. napus Xiang5A underwent nearly complete triplication and allotetraploidy relative to Arabidopsis thaliana. Using the gap-free assembly, we found that 917 flowering-related genes were affected by structural variation, including BnaA03.VERNALIZATION INSENSITIVE 3 and BnaC04.HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1. These genes may play crucial roles in regulating flowering time and facilitating the adaptation of Xiang5A in the Yangtze River Basin of China. This reference genome provides a valuable genetic resource for rapeseed functional genomic studies and breeding.

Brassica napus L. is a vital oil crop and exhibits notable salt tolerance, making the enhancement of this trait crucial for cultivation in saline soils. Uncovering its underlying mechanism may further heighten the salt tolerance of B. napus. In this study, we conducted a genome-wide analysis of the Root Meristem Growth Factor (RGF) gene family in Brassica species and identified BnaRGF8 as a key regulator of salt tolerance. Under 200 mM NaCl treatment, all RGF genes were induced, with BnaRGF8 showing the greatest upregulation. This response was consistently observed across 10 genotypes, indicating a universal trend in B. napus. Functional characterization revealed that chemically synthesized BnaRGF8 alleviated salt-induced growth inhibition by restoring primary root elongation and lateral root formation. Additionally, BnaRGF8 preserved membrane integrity and maintained cell division under salt stress, establishing itself as a novel anti-salt peptide in B. napus.