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New Phytol. 2016 Sep;211(4):1279-94. doi: 10.1111/nph.13996. Epub 2016 May 23.

Multifunctional oxidosqualene cyclases and cytochrome P450 involved in the biosynthesis of apple fruit triterpenic acids.

Author information

1
Department of Environmental Research and Innovation, Luxembourg Institute of Science and Technology, Avenue des Hauts-Fourneaux, L-4362, Esch/Alzette, Luxembourg.
2
Institut des Sciences de la Vie, UCLouvain, B-1348, Louvain-la-Neuve, Belgium.
3
The New Zealand Institute for Plant & Food Research Limited, Mt Albert Research Centre, Private Bag 92 169, Auckland, 1142, New Zealand.
4
The New Zealand Institute for Plant & Food Research Limited, Ruakura, Hamilton, 3240, New Zealand.
5
Walloon Agricultural Research Centre, Rue de Liroux, B-5030, Gembloux, Belgium.

Abstract

Apple (Malus × domestica) accumulates bioactive ursane-, oleanane-, and lupane-type triterpenes in its fruit cuticle, but their biosynthetic pathway is still poorly understood. We used a homology-based approach to identify and functionally characterize two new oxidosqualene cyclases (MdOSC4 and MdOSC5) and one cytochrome P450 (CYP716A175). The gene expression patterns of these enzymes and of previously described oxidosqualene cyclases were further studied in 20 apple cultivars with contrasting triterpene profiles. MdOSC4 encodes a multifunctional oxidosqualene cyclase producing an oleanane-type triterpene, putatively identified as germanicol, as well as β-amyrin and lupeol, in the proportion 82 : 14 : 4. MdOSC5 cyclizes 2,3-oxidosqualene into lupeol and β-amyrin at a ratio of 95 : 5. CYP716A175 catalyses the C-28 oxidation of α-amyrin, β-amyrin, lupeol and germanicol, producing ursolic acid, oleanolic acid, betulinic acid, and putatively morolic acid. The gene expression of MdOSC1 was linked to the concentrations of ursolic and oleanolic acid, whereas the expression of MdOSC5 was correlated with the concentrations of betulinic acid and its caffeate derivatives. Two new multifuntional triterpene synthases as well as a multifunctional triterpene C-28 oxidase were identified in Malus × domestica. This study also suggests that MdOSC1 and MdOSC5 are key genes in apple fruit triterpene biosynthesis.

KEYWORDS:

Malus × domestica; apple; betulinic acid; cytochrome P450; germanicol; oxydosqualene cyclase; triterpene; ursolic acid

PMID:
27214242
PMCID:
PMC5089662
DOI:
10.1111/nph.13996
[Indexed for MEDLINE]
Free PMC Article

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