Comparative transcriptome analysis of leaf, stem, and root tissues of Semiliquidambar cathayensis reveals candidate genes involved in terpenoid biosynthesis

Background Semiliquidambar cathayensis is a traditional medicinal plant and endemic species in China. Its roots, branches, leaves, bark, and nectar are known to have therapeutic effects against rheumatoid arthritis, lumbar muscle strain, and several other diseases. However, limited knowledge regarding the molecular properties of S. cathayensis highlights the need for further research in order to elucidate the underlying pathways governing the synthesis of its active ingredients and regulation of its accumulation processes. Methods We conducted transcriptome sequencing of the leaf, stem and root epidermises, and stem and root xylems of S. cathayensis with three biological replicates. Moreover, candidate genes involved in terpenoid biosynthesis, such as IDI, FPPS, DXR, SQS, GPPS, and HMGR were selected for quantitative real-time PCR analysis. Results We identified 88,582 unigenes. Among which, 36,144 unigenes were annotated to the nr protein database, 21,981 to the Gene Ontology database, 11,565 to the Clusters of Orthologous Groups database, 24,209 to the Pfam database, 21,685 to the SWISS-PROT database, and 12,753 to the Kyoto Encyclopedia of Genes and Genomes (KEGG), with 5072 unigenes common to all six databases. Of those annotated using the KEGG database, 187 unigenes were related to the terpenoid metabolism pathway, and expression analysis of the related genes indicated that the mevalonate and methylerythritol 4-phosphate pathways play different roles in terpenoid biosynthesis in different tissues of S. cathayensis. Conclusions These findings greatly expand gene resources of S. cathayensis and provide basic data for the study of the biosynthetic pathways and molecular mechanisms of terpenoids.