Characterising chlorogenic acid biosynthesis in coffee

Knevitt, Daniel (2017) Characterising chlorogenic acid biosynthesis in coffee. Doctoral thesis, University of East Anglia.

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Coffee is an important commodity and a major export for developing countries. There are two commercially grown species: Robusta and Arabica. The latter is more desirable, but more difficult to cultivate. It is susceptible to pests and diseases and less tolerant to environmental changes. This vulnerability is partly due to Arabica accumulating less chlorogenic acid (CGA) than Robusta. There are high levels of CGAs in the coffee beverage which contribute to the flavour and confer health benefits. In this study, I characterised enzymes involved in the biosynthesis of CGAs in coffee and investigated the function of transcription factors in controlling the phenylpropanoid pathway that lead to CGA production.
The enzyme hydroxycinnamoyl-CoA quinate hydroxycinnamoyltransferase (HQT) is entirely responsible for the synthesis of the major CGA, 5-caffeoylquinic acid (5-CQA). I also discovered two routes for the synthesis of dicaffeoylquinic acids (diCQAs) from 5-CQA utilising two different enzymes in different subcellular compartments. HQT could synthesise diCQAs in the presence of high concentrations of 5-CQA when localised to the vacuole. Hydroxycinnamoyl-CoA quinate/shikimate hydroxycinnamoyltransferase (HCT) could synthesise diCQAs through the same route but can also synthesise diCQAs at neutral pH using 5-CQA and caffeoyl CoA. Tissue distribution patterns of metabolites in developing coffee fruit confirmed the presence of these biosynthetic routes.
I cloned and characterised several R2R3MYB genes encoding potential regulators of CGA biosynthesis. Their analysis also led to a possible explanation for the usually high levels of CGA in coffee. Distinct MYB12-like transcription factors activated the transcription of a non-functional chalcone synthase (CHS) gene which is important for the synthesis of flavonols. This results in high levels of CGAs at the expenses of flavonol accumulation. Understanding CGA biosynthesis in coffee will be useful for sustainable cultivation of this important crop.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Users 4971 not found.
Date Deposited: 23 Jun 2017 12:32
Last Modified: 31 Dec 2018 01:38


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