Magnolia Officinalis , a Chromosome-Scale Genome Reveals Evolution Position of Magnoliids and Contributes to Lignan Biosynthesis

Magnolia officinalis, a representative tall aromatic tree of the Magnoliaceae family, is a widely used medicinal plants with diverse medicinal values and applications, such as afforestation, ornamental and so on. We report a chromosome‑scale draft genome of M. officinalis, in which ~ 99.66% of the sequences were anchored onto 19 chromosomes with the scaffold N50 of 76.62 Mb. We found that a high proportion of repetitive sequences was a common feature of three Magnoliaceae with known genomic data, and M. officinalis was the plant in Magnoliaceae with the highest ratio of repetitive sequences found so far. Phylogenetic analyses reveal that magnoliids are as sister to the eudicots-monocots clade, which provides insight into the phylogenetic position between eudicots and monocots. WGD analysis showed that an ancient duplication event occurred in the M. officinalis genome, is shared by Lauraceae. Based on gene functional annotations and RNA-seq, we identified several key enzyme-coding gene families associated with the biosynthesis of lignan in the genome. In addition, the floral fragrance of M. officinalis is mainly attributed to its terpenes, we classified many putative genes involved in the biosynthesis of terpene synthases. The construction of the M. officinalis genome sequence map will serve as a reference for further studies of Magnolia as well as other Magnoliaceae.