A chaperonin BnaC01.CCT8 contributes to silique length and seed weight by affecting auxin and jasmonic acid signalling in Brassica napus.

Seed weight (SW), which is directly influenced by silique length (SL), is a critical agronomic trait significantly affecting both the quality and yield of rapeseed. In this study, a shorter silique length (ssl) mutant was generated through ethyl methane sulfonate mutagenesis, exhibiting reduced SL and SW compared to the wild type. Utilizing a map-based cloning approach, BnaC01.CCT8, a member of the chaperonin containing T-complex polypeptide-1 (CCT) family, was identified as the gene responsible for restoring the ssl phenotype. A missense mutation from alanine to valine (A507V) in BnaC01.CCT8 was identified as crucial for its functional activity, as evidenced by the genetic complementation of BnaC01.CCT8 and BnaC01.CCT8 in the Arabidopsis cct8-2 background. Moreover, overexpression of BnaC01.CCT8 in Brassica napus significantly enhanced SL, SW and seed yield per plant. Conversely, CRISPR/Cas9-mediated bnac01.cct8 knockout lines exhibited reduced SL and SW. Transcriptome analysis and hormone content detection indicated that BnaC01.CCT8 positively regulated SL and SW primarily by modulating auxin and jasmonic acid signalling, thereby affecting the length of epidermal cells in the silique wall. Furthermore, BnaC01.CCT8 interacted with BnaA09.ARF18 (AUXIN-RESPONSE FACTOR 18), contributing to the regulation of SL and SW, while the A507V mutation disrupted this interaction. Haplotype analysis demonstrated that several SNP differences in BnaC01.CCT8 were significantly associated with variations in SL and SW among germplasm resources, revealing superior alleles of BnaC01.CCT8. The identification and functional analysis of BnaC01.CCT8 provide new insights into the mechanisms regulating SL and SW and present a valuable target for the genetic enhancement of rapeseed yield.