Dynamic metabolic and transcriptomic profiling reveal synthetic characters and regulators of flavonoid biosynthesis in Camellia oleifera seeds

Flavonoids are natural bioactive substances with beneficial health effects against chronic diseases. Camellia oleifera Abel. (C. oleifera) has attracted attention because its seeds contain high levels of unsaturated fatty acids. Actually, flavonoids are also abundant in the C. oleifera seeds. However, the composition and distribution of flavonoid and overall molecular mechanism of flavonoid biosynthesis in the C. oleifera seeds have not been fully uncovered. To this end, metabolome, transcriptome, high-performance liquid chromatography, microscopic, and exogenous methyl jasmonate treatment analyses of C. oleifera seeds at different developmental stages were performed. Results revealed that the differential metabolites and genes were enriched in the flavonoid biosynthesis pathways in C. oleifera seeds. Flavonoid profiles presented dynamic patterns that changed with seed development, consistent with the pattern of gene regulation in the corresponding pathways. In total, 52 differentially accumulated flavonoids and 124 differentially expressed structural genes involved in flavonoid biosynthesis were identified. After weighted gene co-expression network analysis, three modules were highly interrelated with the accumulation of flavonoid components. The co-expression networks of these three modules were used to identify key candidate transcription factors associated with flavonoid biosynthesis, such as MYC2, bHLH3, bHLH18, MYB44, MYB86, WRKY26, and WRKY32. Based on these differentially accumulated flavonoids and key genes, the genetic and metabolic regulatory networks of flavonoid biosynthesis was proposed. Moreover, exogenous methyl jasmonate influenced the accumulation of diverse flavonoids in C. oleifera seeds. Potential regulatory factors identified in this study will contribute to the provision of molecular traces for in-depth research on flavonoid biosynthesis and product development for C. oleifera with higher value.