Molecular regulation of fatty acid biosynthesis and oil composition during olive drupe ripening

Coordinated transcriptional networks orchestrate fatty acid and triacylglycerol synthesis in olives, with ABA signaling and specific transcription factors regulating lipid pathways that define extra-virgin olive oil quality. Health benefits of olive oil are due to the unique fatty acid (FA) profile. However, the transcriptional mechanisms regulating FA biosynthesis during drupe ripening are poorly understood. Herein, we coupled transcriptomics, targeted FA profiling and weighted gene co-expression network analysis (WGCNA) to dissect lipid metabolism through four developmental stages of 'Koroneiki' drupes. FA quantification revealed a progressive decline in saturated fatty acids (SFAs) alongside a steady rise in monounsaturated (MUFAs) and polyunsaturated fatty acids (PUFAs), notably oleic and linoleic acids. Transcriptome analysis identified 42 core genes of FA metabolism and triacylglycerol (TAG) biosynthesis. WGCNA revealed distinct transcriptional modules linked to progressive SFA reduction, late-stage MUFA accumulation and PUFA synthesis during drupe ripening. Expression of the saturation pathway genes progressively downregulated contrary to the desaturation pathway counterparts that determine the final oil composition leading to oleic acid prevalence. Intriguingly, ABA-biosynthesis and signaling genes were co-expressed with MUFA/PUFA modules, supporting a central role of ABA in late-stage lipid biosynthesis. Moreover, ABA-mediated regulation of lipid metabolism appeared to be fine-tuned by the contrasting expression of distinct PP2C homologs and coordinated by specific transcription factors. The expression dynamics of stearoyl-ACP desaturase SAD4 and the TAG assembly enzyme PDAT1 identify them as molecular markers of the transition from saturated to unsaturated fatty acids, leading to oleic acid enrichment during ABA-regulated olive drupe ripening. Overall, we present an integrated systems-level framework of the transcriptional networks driving olive oil biosynthesis, outlining a molecular toolbox to enhance extra virgin olive oil yield and quality.