Research Progress on Seed Size of Brassica napus Seeds

Brassica napus L. is a member of the family Cruciferae. This species is also referred to as "rape," “oilseed rape," "rapa," "rappi," and "rapeseed." It is the third most important source of edible oil globally after soybean and palm oil. Quantitative trait loci (QTLs) analysis has proven to be a powerful tool to reveal the genetic mechanisms of seed weight regulation in this species. We identified and compiled a comprehensive list of 1,905 candidate genes associated with seed weight regulation in Brassica napus. Five candidate genomic regions with 204 seed weight–related genes were identified, including 21 differentially expressed genes from transcriptomic analysis. A CRISPR/Cas mutant library targeting silique- and seed size-related genes was generated in rapeseed, indicating a potential role of BnaHRDs in their development. DEGs were involved in developmental processes, cell division, and nutrient storage, indicating their role in regulating seed size in Brassica napus. HB1 and HAIKU2 also regulate seed weight by controlling endosperm proliferation through the IKU pathway. A total of 1,643 SNP markers were aligned to the pseudochromosomes of Brassica napus using BLAST to identify significant hits. Furthermore, BRASSINAZOLE-RESISTANT1 (BZR1) is an important regulator of seed growth acting through maternal tissues. TDZ treatment enhanced both cell size and number. Plant hormones, including auxin, gibberellin (GA), and brassinosteroid (BR) signaling pathways, have been reported to regulate seed size. Transcription factors including LEC2, WRI1, FUS3, MYB30, and ABI3 were active during early seed development, while LEC1, LEC2, ABI3, and FUS3 remained active during seed maturation. Physiological processes play a key role in yield variation and the selection of high-yielding genotypes. Currently, marker-assisted selection and transgenic approaches are commonly used in rapeseed breeding. Temperature and light are key environmental factors affecting oil production in rapeseed. The integration of genetic engineering, molecular marker technologies, and conventional selection is expected to be a key approach for improving high-oil-content rapeseed. These limitations highlight the need for further studies on rapeseed applications.