Olive is a valuable oil-bearing tree with fruits containing high levels of fatty acids. Oil production is a multifaceted process involving intricate interactions between fatty acid biosynthesis and other metabolic pathways that are affected by genetics and the developmental stages of the fruit. However, a comprehensive understanding of the underlying regulatory mechanisms is still lacking. Here, we generated a gap-free telomere-to-telomere assembly for Olea europaea cv. ‘Leccino’, representing an olive genome with the highest contiguity and completeness to date. The combination of time-course metabolomics and transcriptomics datasets revealed a negative correlation between fatty acid and flavonoid biosynthesis in the initial phase of olive fruit development, which was subject to an opposing regulatory mechanism mediated by the hub transcription factor MYC2. Multifaceted molecular assays demonstrated that MYC2 is a repressor of fatty acid biosynthesis by downregulating the expression of BCCP2 (biotin carboxylase carrier protein 2), while it acts as an activator of FLS (flavonol synthase), leading to an increase in flavonoid synthesis. Furthermore, the expression of MYC2 is regulated by fluctuations of methyl jasmonate content during olive fruit development. Our study completes a high-quality gapless genome of an olive cultivar, and provides new insight into the regulatory mechanisms underlying the biosynthesis of fatty acids and flavonoids in its fruit.

Olive leaves are rich in phenolic compounds. This study explored the chemical profiles and contents of free phenolics (FPs) and bound phenolics (BPs) in olive leaves, and further investigated and compared the antioxidant properties of FPs and BPs using chemical assays, cellular antioxidant evaluation systems, and in vivo mouse models. The results showed that FPs and BPs have different phenolic profiles; 24 free and 14 bound phenolics were identified in FPs and BPs, respectively. Higher levels of phenolic acid (i.e., sinapinic acid, 4-coumaric acid, ferulic acid, and caffeic acid) and hydroxytyrosol were detected in the BPs, while flavonoids, triterpenoid acids, and iridoids were more concentrated in the free form. FPs showed a significantly higher total flavonoid content (TFC), total phenolic content (TPC), and chemical antioxidant properties than those of BPs (p < 0.05). Within the range of doses (20–250 μg/mL), both FPs and BPs protected HepG2 cells from H₂O₂-induced oxidative stress injury, and there was no significant difference in cellular antioxidant activity between FPs and BPs. The in vivo experiments suggested that FP and BP treatment inhibited malondialdehyde (MDA) levels in a D-galactose-induced oxidation model in mice, and significantly increased antioxidant enzyme activity of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and the total antioxidant capacity (T-AOC). Mechanistically, FPs and BPs exert their antioxidant activity in distinct ways; FPs ameliorated D-galactose-induced oxidative stress injury partly via the activation of nuclear factor erythroid-2-related factor 2 (Nrf2) signaling pathway, while the BP mechanisms need further study.