Metabolomics of Dioscorea spp. (Yam) : Biochemical diversity of an underutilised and understudied crop. / Price, Elliott.

2017. 265 p.

Research output: ThesisDoctoral Thesis

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Abstract

The genus Dioscorea comprises over 600 monocot plants commonly termed “yam”. Of these, five to ten species are cultivated; their edible tubers providing livelihood for ~100 million people. Production occurs almost exclusively in Low Income Food Deficit Countries (LIFDCs) and as such yams are vital for food security. A further fifteen to thirty species are grown, or harvested from the wild, to provide precursors for the industrial production of steroids, with an annual turnover estimated at ~$500-1000 million. In addition, numerous species are widely used in traditional medicines and over-harvesting has endangered many species.
Yams have high-yield potential and high market value potential yet current breeding of yam is hindered by a lack of genomic information and genetic resources. New tools are needed to modernise breeding strategies and unlock the potential of yam to improve livelihood in LIFDCs.
Furthermore, whilst the steroidal precursors of yams have been widely studied, limited research has been conducted on central metabolism of the crop. Recent literature highlighted that experimental flaws, analytical miscalculations and technical imprecision plagues historic studies providing impetus for re-investigation of Dioscorea using modern biochemical techniques.
In the present work Gas Chromatography- Mass Spectrometry (GC-MS) based metabolomic investigation has been applied to collections of yam to assess the diversity of primary metabolism. The GC-MS workflow was applied to a leaf-based collection comprising diverse species across clades of the genus and adapted to analyse tubers of elite lines from the global yam breeding program.
Targeted analyses were undertaken by Liquid Chromatography (LC), coupled with detection by Photo Diode Array (PDA) or MS, to study the carotenoid compositions of breeding lines and survey the constitution of sterols in species previously reported as sterol-rich.GC-MS based metabolite profiling on leaf extracts allowed the separation of genotypes into clades, species and morphological traits with a putative geographical origin. Additionally, the foliage material has been shown to be a potential renewable source of numerous high-value compounds. For example, shikimic acid was quantified to be up to 8% of dry weight in the leaves of species from the Testudinaria clade. Future bioprospecting of foliage can add-value from the waste steam of crop production and may aid species conservation as an alternative to the over-harvested tubers and/ or rhizomes.A visual pathway representation of the tuber metabolome has been delivered as a resource for quality trait evaluation of yam germplasm. Over 200 compounds were routinely measured in tubers, providing a major advance for chemotyping of the crop and chemotaxonomic classifications complemented molecular systematics. Biochemical redundancy within the global yam breeding program has been highlighted and accessions with relatively abundant fatty acid and pro-vitamin A contents identified.Finally, the sterol composition in the leaves and rhizomes of reportedly sterol-rich species was surveyed. The resultant profiles were complex with a large degree of qualitative differences amongst species. Whilst the majorly abundant sterols largely matched those in literature, numerous unknowns, including polyhydroxylated and glycosylated derivatives, were noted. Follow-up investigation will require detailed structural elucidation but the work has provided leads to revisit Dioscorea for new natural products.Overall, the work highlights the potential of exploiting the biochemical diversity of Dioscorea species to achieve food and income security and discover new, sustainable sources of medicines and high-value compounds. The use of metabolomics offers a dual benefit to the global breeding program: it can provide standalone near-future gains and can be complimentary to other ongoing large-scale ‘omic’ investigations.
Original languageEnglish
QualificationPh.D.
Awarding Institution
Supervisors/Advisors
  • Fraser, Paul, Supervisor
  • Wilkin, Paul, Supervisor, External person
  • Sarasan, Viswambharan, Supervisor, External person
Award date1 Jun 2017
Publication statusPublished - 2017
This open access research output is licenced under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

ID: 28081208