Integrated transcriptomic and metabolomic analyses reveal the molecular mechanisms regulating oil accumulation in Oenothera biennis L.

Oenothera biennis L. is a multipurpose plant that can be valued for its seed oil rich in unsaturated fatty acids such as gamma-linolenic acid (GLA), exhibiting notable medicinal and economic importance. To elucidate the unclear mechanisms of its seed oil synthesis, this study examined morphological, biochemical, and molecular aspects of seed development and oil biosynthesis across nine stages. Oil accumulation exhibited four distinct phases: formation (0–12 d post-anthesis (DPA)), rapid accumulation (12–36 DPA), steady accumulation (36–48 DPA), and consumption (48–54 DPA). Morphological analysis showed capsules reached physiological maturity at 36 d, with peak dry weight and dimensional parameters. Linoleic acid constituted over 75 % of the total fatty acids, whereas GLA peaked at 8.18 % at 54 d. The oil bodies were first observed at 18 d via transmission electron microscopy, with a marked increase in number by 42 d and widespread cellular distribution. A total of 880 differentially expressed genes were identified through transcriptome sequencing, enriched in fatty acid synthesis, glycolysis, and plant hormone signaling pathways. Gene co-expression network analysis revealed 12 key genes (including ObFATA (Fatty acyl-ACP thioesterase A), ObFATB (Fatty acyl-ACP thioesterase B), and ObFAD2 (Fatty acid desaturase 2)) strongly correlated with fatty acid content. qRT-PCR confirmed significant upregulation of these genes during the rapid accumulation phase. Additionally, the seed oil exhibited potent antioxidant activity (2,2-diphenyl-1-picrylhydrazyl (DPPH)/2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)) and selective antibacterial effects against Staphylococcus aureus. These findings define the critical stages and molecular regulatory networks of oil biosynthesis in evening primrose seeds, offering a theoretical basis and genetic resources for molecular breeding of high-oil evening primrose varieties.