Identification and functional characterization of a γ-terpinene synthase in Nigella sativa L (black cumin)

Nigella sativa (Black cumin) has many applications in food and pharmaceutical industries. Thymoquinone has been considered as a main effective compound in N. sativa seeds and attracted researchers' attention mainly due to its medicinal potential. In this study, the essential oil components of leaves, flowers and seed developmental stages including half black seeds, soft black seeds and hard black seeds were analyzed in N. sativa. Whereas no terpenes were detected in flowers and leaves, seeds showed an essential oil composition that increased in its thymoquinone content during seed maturation. To study the proposed first step of thymoquinone biosynthesis, the formation of γ-terpinene from geranyl diphosphate (GDP), we identified and functionally characterized a γ-terpinene synthase (NsTPS1) in N. sativa. This monoterpene synthase was identified in RNA sequence data derived from seeds. After heterologous expression in Escherichia coli, partially purified NsTPS1 converted GDP to γ-terpinene. NsTPS1 is the first functionally characterized terpene synthase from N. sativa and displays a higher similarity to other terpene synthases from Ranunculaceae than known γ-terpinene synthases from more distant plant species. Characterization of NsTPS1 elucidates the first dedicated step in the biosynthesis of thymoquinone in N. sativa and paves the way towards metabolic engineering for high-level thymoquinone production.