A squalene epoxidase from Nigella sativa participates in saponin biosynthesis and mediates terbinafine resistance in yeast |
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Authors: | Marta Lipinski Martin Scholz Kay Pieper Rainer Fischer Dirk Prüfer Kai J Müller |
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Institution: | (1) Westphalian Wilhelms-University Münster, Institute for Biochemistry and Biotechnology of Plants (IBBP), 48143 Münster, Germany;(2) Fraunhofer Institute for Molecular Biology and Applied Ecology (FhG IME), 52074 Aachen, Germany |
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Abstract: | Squalene epoxidase catalyzes the formation of 2,3-oxidosqualene from squalene and in plants is the last enzyme common to all
biosynthetic pathways leading to an array of triterpene derivatives like phytosterols, brassinosteroid phytohormones or saponins.
In this work, we present a squalene epoxidase gene (NSSQE1) from the triterpene saponin producing plant Nigella sativa. The gene product showed a high degree of homology to functional squalene epoxidases (SQEs) from Arabidopsis thaliana and was able to complement SQE deficient yeast that harboured a knockout mutation in the underlying erg1 gene. Moreover, the expression of the NSSQE1 gene in ERG1 wild type yeast revealed that NSSQE1 conferred resistance towards terbinafine, an inhibitor of fungal SQEs. The latter suggested
that a terbinafine-dependent NSSQE1 selection marker system can be developed for yeast. The gene NSSQE1 was ubiquitously expressed in all plant tissues analysed, including roots where no triterpene saponins are produced. Therefore,
we argue that NSSQE1 is a housekeeping gene for triterpene metabolism in Nigella sativa. Similar to triterpene saponins, NSSQE1 was up-regulated by methyl jasmonate in leaves and should also be functionally involved in saponin biosynthesis in Nigella sativa. |
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Keywords: | Nigella sativa Ranunculaceae Squalene epoxidase SQE Squalene monooxygenase SQMO Hederin Saponin Triterpenes |
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