Genetic and Molecular Regulation of Seed Size in Brassica napus: Current Knowledge and Breeding Perspectives

Brassica napus L. (rapeseed), a member of the family Brassicaceae, is the world’s third most important oilseed crop for edible oil production, after soybean and palm. Quantitative trait locus (QTL) mapping is a powerful strategy for dissecting the genetic basis of seed weight. In this review, Previous studies summarized a total of 1905 candidate genes associated with seed weight in Brassica napus. Five candidate genomic regions harboring 204 seed-weight-related genes were identified, among which 21 genes were characterized as differentially expressed genes via transcriptomic analysis. Clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) mutant libraries targeting genes related to silique and seed size have been constructed in Brassica napus, revealing that BnaHRD genes play critical roles in seed development. These differentially expressed genes are involved in developmental processes, cell division. and nutrient storage, supporting their functions in seed size regulation. SHB1 and HAIKU2 modulate endosperm proliferation through the IKU pathway, thereby affecting seed weight. BZR1 (brassinazole-resistant 1) acts as a master regulator of seed growth via maternal tissues. Thidiazuron (TDZ), a cytokinin analogue, simultaneously promotes cell proliferation and cell expansion, thereby increasing cell number and cell size. Multiple phytohormone signaling pathways, including auxin, gibberellin (GA), and brassinosteroid (BR), as well as transcription factors such as LEC2, participate in the regulatory network of seed size. Here, we review current advances in the genetic and molecular regulation of seed size and discuss future perspectives for rapeseed breeding.