Genetic characterization and mechanistic insights into high seed oil content and orange petal trait in the rapeseed mutant opm1

Seed oil content (SOC) is a key quantitative trait in Brassica napus that strongly influences oil yield. However, despite its significance, the genetic basis of natural variation in SOC remains only partially understood. To this purpose, we identified a high-oil, orange-petal mutant (opm1) from an EMS-mutagenized Zhongshuang 11 (ZS11) population. Bulked segregant analysis pinpointed the causal locus for the flower-color phenotype to a single-nucleotide mutation in BnaC09.ZEP, which encodes zeaxanthin epoxidase. However, segregation and linkage analyses showed that the SOC increasement segregates independently of the BnaC09.ZEP mutation, indicating at least one additional causal factor for oil accumulation in opm1. Transcriptomic and enzymatic analyses of opm1 seeds revealed stage-specific reprogramming of lipid metabolism. At early developmental stages, genes involved in fatty acid synthesis and oil body formation were transcriptionally activated, supporting enhanced TAG production. During late maturation, expression of lipid catabolic genes, including GDSL-type esterases, was repressed, accompanied by reduced lipase activity. Despite unchanged oil body morphology, opm1 exhibited reduced seed coat content, collectively contributing to elevated seed oil accumulation. Overall, our findings provide new insights into the regulation of seed oil metabolism and identify a valuable genetic resource for improving oil content in rapeseed.