Terpenoid biosynthesis in Dendrobium officinale: Identification of (E)-β-caryophyllene synthase and the regulatory MYB genes

Dendrobium officinale Kimura et Migo is a well-known medicinal plant producing terpenoid alkaloids as the main medicinal constituents. D. officinale also produces many volatile terpenoids, including monoterpenes and sesquiterpenes. However, little is known about the biosynthetic and regulatory mechanisms underlying terpenoid biosynthesis in this plant. This study first analyzed the terpenoid profiles of D. officinale PLBs treated with lovastatin (LOV) and fosmidomycin (FOS), two chemical inhibitors of terpenoid pathways, and produced corresponding transcriptomes. The volatile products of PLBs were mainly sesquiterpenes, and the contents of (E)-β-caryophyllene and α-humulene were decreased by 42.05% and 27.27%, respectively, after LOV treatment. A candidate sesquiterpene synthase gene identified from the transcriptome and terpene metabolic profiling as (E)-β-caryophyllene synthase (DoECS), localized in the cytoplasm. The emission of (E)-β-caryophyllene decreased by 26.70% in DoECS RNA interference PLBs compared with the control group. Based on co-expression analysis, four MYB genes (DoMYB26, DoMYB29, DoMYB31 and DoMYB32) were involved in the transcriptional regulation of DoECS. Yeast one-hybrid assays and fluorometric GUS assay provided evidence that DoMYB26 and DoMYB31 positively regulated the expression of DoECS, while DoMYB29 negatively regulated the expression of DoECS. In summary, this study produced novel knowledge about the catalytic and regulatory mechanisms responsible for the biosynthesis of volatile terpenoids in D. officinale.