Overexpression of geranyl diphosphate synthase small subunit 1 (LcGPPS.SSU1) enhances the monoterpene content and biomass

Abstract Litsea cubeba (Lour.) Person, an economically important aromatic plant producing essential oils, has lemon-like fragrance and 96.44–98.44% monoterpene contents. Understanding the rate-limiting enzymes in the biosynthesis of monoterpenes in L. cubeba serves the purpose of designing of new approaches to metabolic engineering. In this study, we investigated the function of geranyl diphosphate synthase small subunit 1 (LcGPPS.SSU1), a branchpoint gene of monoterpenes biosynthesis pathway in L. cubeba. The expression analysis showed that LcGPPS.SSU1 was highly expressed in fruits, where the essential oil was produced and stored, and induced by light and methyl jasmonate (MeJA). In addition, the promoter of LcGPPS.SSU1 could drive the trichome-specific expression in tobacco. Overexpression of LcGPPS.SSU1 enhanced the monoterpene production in L. cubeba and tobacco (Nicotiana benthamiana). Moreover, analysing the expression level analysis of the key genes, especially 1-deoxy-D-xylulose 5- phosphate synthase (DXS), involved in mevalonic acid (MVA) and methylerythritol phosphate (MEP) pathway showed the metabolic flux was increased by positive feedback regulation mechanism in LcGPPS.SSU1-overexpressing lines. Meanwhile, when MEP pathway flux increased, the seed yield, leaf area, plant height of LcGPPS.SSU1-overexpressing lines were enhanced by elevating the MEP-derived primary metabolites, such as gibberellin (GA), due to the increased expression levels of geranylgeranyl diphosphate synthases 2 (GGPPS2), GGPPS4 and GA20-oxidase (GA20ox). Taken together, our results suggest that LcGPPS.SSU1 plays a vital role in monoterpenes biosynthesis.