The updated weeping forsythia genome reveals the genomic basis for the evolution and the forsythin and forsythoside A biosynthesis

Weeping forsythia (Forsythia suspensa, Oleaceae) is a deciduous broad-leaved tree species distributed in the warm temperate zone of China. However, the species still lacks a chromosome-level genome. In this study, the former draft genome (Accession No. WIPI00000000) of weeping forsythia was assembled into 14 chromosomes with a 712.9 Mb genome size. Weeping forsythia underwent α and β whole-genome duplication events. After the divergence between weeping forsythia and Olea europaea, 1453 gene families had a significant expansion, and 1146 gene families had a significant contraction. The enrichment pathways and ontologies of expanded genes suggested that the tillering, photosynthesis and growth capacity of weeping forsythia were enhanced after the divergence of weeping forsythia and O. europaea. The contracted genes suggested that the resistance of weeping forsythia to cold and drought was weakened. The last glacial period led to a significant decline in the effective population size of weeping forsythia. Forty-six candidate genes were identified for the synthesis of the forsythin and forsythoside A by genomic and transcriptomic data. In this study, we improved the previous draft genome of weeping forsythia. Our genome will provide genomic resources for the subsequent evolution and breeding research of weeping forsythia.