Ketocarotenoid production in Solanum lycopersicum; biosynthesis and sequestration

Esther Ruth Lewis

Research output: ThesisDoctoral Thesis

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Carotenoids are natural pigments with important antioxidant properties. Commercially they have been exploited across multiple industrial sectors, including aquaculture, health supplements, and food-related industries. Currently carotenoids are produced predominantly by chemical synthesis using precursors from the petrochemical industry. The unfavourable environmental impact of these procedures means new sustainable production platforms are being sought with rapidity. The production of ketocarotenoids is especially desirable, with industries such as aquaculture reliant on their pigmentation and antioxidant effects.
Previous work has led to the biosynthesis of ketocarotenoids and ketocarotenoid esters in tomato fruit. The bacterial genes carotenoid hydroxylase (CrtZ) and oxygenase (CrtW) have been combined with the overexpression of lycopene β-cyclase (cyc-b). The present study focusses on improvement of the previous approach to ketocarotenoid production, firstly by addition of beta carotene hydroxylase (CrtR-b2), and secondly using a single, multigene construct designed for ketocarotenoid production. The addition of CrtR-b2 has increased the amount of astaxanthin produced within tomato fruit to 650 μg/g. However, the complexity of the background means each generation has a complicated segregation pattern, and the resulting screening is laborious. Therefore, an alternative approach is desirable. The use of a single, multigene construct has been employed to transform CrtW, CrtR-b2 and an alternative cyclase, lycopene beta-cyclase (lcy) into tomato. Stable transformation of this multigene construct resulted in a T0 generation which accumulated predominantly lycopene, however the ketocarotenoids astaxanthin and phoenicoxanthin were also produced.
Esterification plays an important role in the bioavailability and sequestration of the ketocarotenoids. As carotenoid esterification does not normally occur in tomato fruit, the gene responsible for this process is unknown. The pale yellow petal (pyp) gene has previously been identified as an important acyltransferase in tomato flower, with mutants displaying a paler petal phenotype and a lack of carotenoid esters. In this work the ketocarotenoid producing genotype has been genetically crossed with the pyp-1 mutant line in order to elucidate the potential role of pyp in esterification of ketocarotenoids. The presence of the pyp mutation in ketocarotenoid producing fruit caused a complete absence of carotenoid esters, this corroborates that the pyp gene is necessary and involved in the esterification of ketocarotenoids in fruit.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Fraser, Paul, Supervisor
Award date1 Aug 2020
Publication statusUnpublished - 31 Mar 2020


  • Ketocarotenoids
  • Carotenoid esters
  • Golden Gate
  • Esterification
  • Astaxanthin
  • Fruit Specific Promoters
  • Gene Silencing

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