Stage-Resolved Metabolomics of Fruit Development and Oil Accumulation in Idesia polycarpa

Idesia polycarpa is an emerging woody oil tree valued for its fruit oil, yet the developmental coordination of oil accumulation with fruit physiology and metabolism remains insufficiently resolved. Here, we combined fruit phenotyping, proximate composition analysis, enzyme assays, targeted fatty-acid quantification, and untargeted metabolomics to characterize oil accumulation across five key developmental stages (A1-A5). Fruit oil content increased sigmoidally as moisture declined, and acetyl-CoA carboxylase (ACCase) activity peaked early, coinciding with the rapid oil-gain phase. Untargeted LC-MS/MS detected 2145 metabolites, among which 26 lipid-related candidate metabolites were identified and enriched in pathways associated with fatty-acid metabolism and lipid remodeling. Targeted GC-MS quantified 22 fatty acids, including four species that increased toward maturity. Integrated correlation analyses revealed stage-dependent associations among hormones, minerals, and lipid-related traits, including positive associations between oil content and P/K during specific developmental windows. All multi-endpoint tests were adjusted using the Benjamini-Hochberg false-discovery rate. Metabolites in the α-linolenic acid/oxylipin-jasmonate branch showed coordinated, stage-specific shifts, but we interpret this axis as a hypothesis-generating candidate rather than a demonstrated driver of oil accumulation. Overall, our results provide a stage-resolved metabolite framework and candidate stage markers for harvest timing and target selection for subsequent functional validation in Idesia. Because this dataset was generated from a single growing season and one provenance background, the reported temporal patterns should be considered single-season observations pending multi-year and/or multi-genotype validation.