The reference genome of Camellia chekiangoleosa provides insights into Camellia evolution and tea oil biosynthesis

Camellia oil extracted from Camellia seeds is rich in unsaturated fatty acids and secondary metabolites beneficial to human health. However, no oil-tea tree genome has yet been published, which is a major obstacle to investigating the heredity improvement of oiltea trees. Here, using both Illumina and PicBio sequencing technologies, we present the first chromosome-level genome sequence of the oil-tea tree species Camellia chekiangoleosa Hu. (CCH). The assembled genome consists of 15 pseudochromosomes with a genome size of 2.73 Gb and a scaffold N50 of 185.30 Mb. At least 2.16 Gb of the genome assembly consists of repetitive sequences, and the rest involves a high-confidence set of 64608 protein-coding gene models. Comparative genomic analysis revealed that the CCH genome underwent a whole-genome duplication event shared across the Camellia genus at similar to 57.48 MYA and a gamma-WGT event shared across all core eudicot plants at similar to 120 MYA. Gene family clustering revealed that the genes involved in terpenoid biosynthesis have undergone rapid expansion. Furthermore, we determined the expression patterns of oleic acid accumulation- and terpenoid biosynthesis-associated genes in six tissues. We found that these genes tend to be highly expressed in leaves, pericarp tissues, roots, and seeds. The first chromosome-level genome of oil-tea trees will provide valuable resources for determining Camellia evolution and utilizing the germplasm of this taxon.