Haplotype-phased genome unveils the butylphthalide biosynthesis and homoploid hybrid origin of <i>Ligusticum chuanxiong</i>.

Abstract

Butylphthalide is one of the first-line drugs for ischemic stroke therapy, while no biosynthetic enzyme for butylphthalide has been reported. Here, we present a haplotype-resolved genome of <i>Ligusticum chuanxiong</i>, a long-cultivated and phthalide-rich medicinal plant in Apiaceae. On the basis of comprehensive screening, four Fe(II)- and 2-oxoglutarate-dependent dioxygenases and two CYPs were mined and further biochemically verified as phthalide C-4/C-5 desaturases (P4,5Ds) that effectively promoted the forming of (<i>S</i>)-3-<i>n</i>-butylphthalide and butylidenephthalide. The substrate promiscuity and functional redundancy featured for P4,5Ds may contribute to the high phthalide diversity in <i>L. chuanxiong</i>. Notably, comparative genomic evidence supported <i>L. chuanxiong</i> as a homoploid hybrid with <i>Ligusticum sinense</i> as a potential parent. The two haplotypes demonstrated exceptional structure variance and diverged around 3.42 million years ago. Our study is an icebreaker for the dissection of phthalide biosynthetic pathway and reveals the hybrid origin of <i>L. chuanxiong</i>, which will facilitate the metabolic engineering for (<i>S</i>)-3-<i>n</i>-butylphthalide production and breeding for <i>L. chuanxiong</i>.