Fine Mapping of QTL cqSW.A07 for Thousand-seed Weight in Brassica rapa L.

Thousand-seed weight (TSW) is a key determinant of rapeseed yield. In this study, we constructed a high-density genetic linkage map using reduced-representation genome sequencing of 230 F2 individuals derived from a cross between the large-seed Brassica rapa variety Dahuang and the small-seed variety Haoyou 11. A major QTL for TSW, cqSW.A07, was identified on chromosome A07 and fine-mapped to a 115.06 kb interval using residual heterozygous lines and near-isogenic lines. Integrating gene annotation, Arabidopsis homology analysis, and qRT-PCR, BraA07g035320.3C (designated BraA07.TAA1), encoding a tryptophan aminotransferase homologous to Arabidopsis TAA1/TAR, was identified as the most probable candidate gene. Sequence comparison of the two alleles revealed 31 amino acid substitutions. These results provide a molecular basis for high-yield breeding of Brassica rapa.