Researchers led by WANG Guodong from the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences have provided genetic evidence that geranylfarnesyl diphosphate synthases (GFPPSs) are responsible for sesterterpene production in Arabidopsis. 

Plants synthesize over 170,000 terpenoids with diverse ecological functions to help them survive in their local environment. Despite their vast structural and functional diversity, terpenoids are de novo synthesized from only two common C5 precursors, namely, isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP). These two precursors can be generated from either of two independent pathways: the cytosolic mevalonate pathway and the plastidial methylerythritol phosphate (MEP) pathway. 

Sesterterpenes (C25), a poorly understood group of terpenoids, are widespread in the plant kingdom. Upstream enzymes, such as geranylfarnesyl diphosphate synthase (GFPPS, C25) and sesterterpene synthase (sesterTPS), have been extensively studied at the biochemical level. It is noteworthy that plant GFPPSs were evolved from plant GGPPS (C20, a hub enzyme in terpene network) via gene duplication and subsequent neofunctionalization.  

In this study, the researchers found that blockage of the sesterterpene pathway at GFPPS step increased the production of GGPP-derived terpenes. Unexpectedly, they also found that coexpression of sesterTPSs in GFPPS-OE plants rescued the phenotypic changes of GFPPS-OE plants by restoring the endogenous GGPP.  

Using a variety of techniques, they found that in addition to precursor (DMAPP/IPP) competition by GFPPS and GGPPS in plastids, GFPPS directly reduced the activity of GGPPS through protein-protein interaction. The common heteromerization of GFPPS and GGPPS was also discovered in other plant species, but with different biochemical results. 

This study not only deepens our understanding of the catalytic regulation of plastidial terpeneoid biosynthesis, but also provides materials for elucidating the physiological functions of plant sesterterpenes. 

Results were published online in Journal of Integrative Plant Biology entitled "Heteromerization of Short-Chain trans-Prenyltransferase Controls Precursor Allocation within a Plastidial Terpenoid Network". 

This work was supported by grants from the National Key R&D Program of China, the National Natural Science Foundation of China, and the State Key Laboratory of Plant Genomics of China.