Comparative transcriptome analyses of three medicinal Forsythia species and prediction of candidate genes involved in secondary metabolisms [Forsythia suspensa]

Here, de novo transcriptome assemblies for leaf and flower tissues of Forsythias were performed, resulting in 81913 unigenes of F. suspensa, 88491 unigenes of F. viridissima and 69458 unigenes of F. koreana (F. viridissima var. koreana). Classification of the annotated unigenes by gene ontology terms and KEGG pathways was used to explore transcriptomic differences among the Forsythias. Orthogroup was introduced to compare expression levels of unigenes in tissues from different species, which unveiled that three leaf tissues of Fosythias were closely correlated based on expression values of orthologous unigenes. Showing high expression mainly in leaves of F. viridissima and F. koreana, candidate homologs for genes involved in the biosynthetic pathway of lignans and phenylethanoid glycosides were determined in these transcriptome assemblies. Examination of flower and leaf tissues of Forsythia suspensa, F. viridissima and F. viridissima var. koreana