Transitions from polyphenol and phytosterol to oil accumulation in developing Camellia seeds.

Camellia oil is rich in polyphenols and phytosterols, whose accumulation during seed development influences both nutritional and functional quality. To understand how these compounds are biosynthesized and coordinated with primary metabolism, we profiled dynamic changes in polyphenols, phytosterols, and primary metabolites across four developmental stages of Camellia seeds. Early stages exhibited active carbohydrate metabolism, providing carbon precursors for polyphenol and phytosterol production to support seed coat formation and stress defense. During maturation, carbon flux shifted from secondary metabolites toward storage lipids, accompanied by increasing triacylglycerol and oleic acid levels. Metabolomic analysis identified 43 polyphenols and 2 phytosterols, while transcriptome data revealed 127 differentially expressed genes in polyphenol pathways and 13 genes in steroid biosynthesis. These results reveal the coordinated gene and metabolite networks underlying secondary metabolite biosynthesis and carbon flux transitions, providing molecular targets for improving oil quality and bioactive compound content in Camellia seeds.