Transcriptome and metabolome analysis reveals the mechanism of key nutrient formation in Hainan oil-camellia (Camellia hainanica) growth cycle

Hainan oil-camellia ( Camellia hainanica , HOC), a newly discovered tropical decaploid oil-camellia species in Hainan, China, produces a superior quality camellia oil locally named as ‘Shanyou oil’. ‘Shanyou oil’ has a higher nutritional value and contains richer bioactive components than the widely cultivated hexaploid oil-camellia species ( Camellia oleifera ). To systematically investigate the gene expression and metabolite accumulation profiles of HOC throughout its growth cycle, we collected 13 samples for transcriptome sequencing and UPLC-MS/MS metabolomic analysis. A total of 33,462 expressed genes and 577 metabolites were identified. All expressed genes were classified into 10 gene clusters via K-means analysis. Lipids, amino acids, and flavonoids were found abundant in seeds, leaves and floral organs of HOC. GO and KEGG pathway enrichment analyses indicated that genes in cluster 2, 4, and 6 were significantly enriched in flavonoids, lipids, and amino acids metabolic pathways. Further analysis revealed that the up-regulation of KAS II and SAD , alongside the down-regulation of FAD2 and FAD3 , resulting in the high proportion of unsaturated fatty acids (C18:1) in ‘Shanyou oil’. Additionally, two strongly associated transcriptional factors (TFs) modules were predicted participating in the regulation of lipid biosynthesis in HOC. Metabolomic analysis also showed catechins and epicatechins were abundant in many tissues, corresponding with the high expression of related biosynthetic genes. In addition, theanine was found significantly enriched in leaves and seeds. However, its biosynthetic genes high expressed in roots and leaves, suggesting that theanine may be synthesized in the roots and leaves before being transported and accumulated in the seeds. These findings provide valuable data and theoretical support for understanding the higher nutritional value of 'Shanyou oil' and offer a scientific basis for the further development and utilization of HOC. • Comprehensive transcriptomic and metabolic profiling across Hainan oil-camellia's growth cycle. • Mechanistic insights into C18:1, catechins and theanine accumulation in Hainan oil-camellia. • Biosynthetic pathways and regulatory network mapping of lipids, catechins and theanine in Hainan oil-camellia.