Modules of co-regulated metabolites in turmeric (Curcuma longa) rhizome suggest the existence of biosynthetic modules in plant specialized metabolism

Turmeric is an excellent example of a plant that produces largenumbers of metabolites from diverse metabolic pathways or networks.It is hypothesized that these metabolic pathways or networkscontain biosynthetic modules, which lead to the formation ofmetabolite modules—groups of metabolites whose productionis co-regulated and biosynthetically linked. To test whethersuch co-regulated metabolite modules do exist in this plant,metabolic profiling analysis was performed on turmeric rhizomesamples that were collected from 16 different growth and developmenttreatments, which had significant impacts on the levels of 249volatile and non-volatile metabolites that were detected. Importantly,one of the many co-regulated metabolite modules that were indeedreadily detected in this analysis contained the three majorcurcuminoids, whereas many other structurally related diarylheptanoidsbelonged to separate metabolite modules, as did groups of terpenoids.The existence of these co-regulated metabolite modules supportedthe hypothesis that the 3-methoxyl groups on the aromatic ringsof the curcuminoids are formed before the formation of the heptanoidbackbone during the biosynthesis of curcumin and also suggestedthe involvement of multiple polyketide synthases with differentsubstrate selectivities in the formation of the array of diarylheptanoidsdetected in turmeric. Similar conclusions about terpenoid biosynthesiscould also be made. Thus, discovery and analysis of metabolitemodules can be a powerful predictive tool in efforts to understandmetabolism in plants. Key words: Biosynthesis, Curcuma longa, curcumin, metabolite module, metabolomics, rhizome, specialized metabolismReceived 16 June 2008; Revised 29 September 2008 Accepted 2 October 2008