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Combinatorial biochemistry of triterpene saponins in plants

Jacob Pollier (UGent)
(2011)
Author
Promoter
(UGent)
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Abstract
Plants are capable of synthesizing an overwhelming variety of secondary metabolites, many of which possess biological activities relevant for the pharmaceutical and chemical industries. Furthermore, there is an ever increasing demand for novel compounds, due to, among others, the growing drug tolerance and resistance in microorganisms and newly emerging diseases. In microorganisms, combinatorial biochemistry is a widely used tool to increase structural variation in several classes of (microbial) natural products. Despite the potential importance of plant secondary metabolites, only a limited fraction of these molecules is currently used, mostly due to their complex structure and the low production levels in planta. Metabolic engineering of plants has offered limited help because the molecular mechanisms steering plant secondary metabolism remain poorly characterized. Here, we used a functional genomics approach to identify candidate genes involved in the saponin biosynthesis of five different plants. After targeted metabolite profiling confirmed the induction of triterpene saponin biosynthesis by methyl jasmonate treatment, a genome-wide cDNA-AFLP transcript profiling was carried out for the five plants. Taking into account the putative functional annotation and the expression pattern of the visualized transcript tags, a set of 259 candidate genes potentially involved in saponin biosynthesis and its regulation were identified. The generated gene list provided the basis for a combinatorial biochemistry platform that targets triterpene saponins in plants. Proof of concept of combinatorial biochemistry was achieved by heterologous expression of the candidate saponin biosynthesis genes in M. truncatula hairy roots. Three of the generated transgenic hairy root lines were found to accumulate novel molecules, two of which were shown to be novel triterpene saponins, whereas the third line produced a set of novel, non-saponin compounds. Furthermore, the identified transcription factors and other regulators were lead candidates for studies investigating the control of the saponin biosynthesis in planta. This led to the identification of a RING membrane-anchor E3 ubiquitin ligase, MAKIBISHI1 (MKB1), that targets 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), the enzyme catalyzing the rate-limiting step in the mevalonate pathway, for ubiquitin-mediated proteasomal degradation, thereby controlling saponin biosynthesis.
Keywords
Transcript Profiling, Triterpene Saponins, Combinatorial Biochemistry, Natural Products, Secondary Metabolites, Metabolite Profiling

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Citation

Please use this url to cite or link to this publication:

Chicago
Pollier, Jacob. 2011. “Combinatorial Biochemistry of Triterpene Saponins in Plants”. Ghent, Belgium: Ghent University. Faculty of Sciences.
APA
Pollier, J. (2011). Combinatorial biochemistry of triterpene saponins in plants. Ghent University. Faculty of Sciences, Ghent, Belgium.
Vancouver
1.
Pollier J. Combinatorial biochemistry of triterpene saponins in plants. [Ghent, Belgium]: Ghent University. Faculty of Sciences; 2011.
MLA
Pollier, Jacob. “Combinatorial Biochemistry of Triterpene Saponins in Plants.” 2011 : n. pag. Print.
@phdthesis{1853820,
  abstract     = {Plants are capable of synthesizing an overwhelming variety of secondary metabolites, many of which possess biological activities relevant for the pharmaceutical and chemical industries. Furthermore, there is an ever increasing demand for novel compounds, due to, among others, the growing drug tolerance and resistance in microorganisms and newly emerging diseases. In microorganisms, combinatorial biochemistry is a widely used tool to increase structural variation in several classes of (microbial) natural products. Despite the potential importance of plant secondary metabolites, only a limited fraction of these molecules is currently used, mostly due to their complex structure and the low production levels in planta. Metabolic engineering of plants has offered limited help because the molecular mechanisms steering plant secondary metabolism remain poorly characterized. Here, we used a functional genomics approach to identify candidate genes involved in the saponin biosynthesis of five different plants. After targeted metabolite profiling confirmed the induction of triterpene saponin biosynthesis by methyl jasmonate treatment, a genome-wide cDNA-AFLP transcript profiling was carried out for the five plants. Taking into account the putative functional annotation and the expression pattern of the visualized transcript tags, a set of 259 candidate genes potentially involved in saponin biosynthesis and its regulation were identified. The generated gene list provided the basis for a combinatorial biochemistry platform that targets triterpene saponins in plants. Proof of concept of combinatorial biochemistry was achieved by heterologous expression of the candidate saponin biosynthesis genes in M. truncatula hairy roots. Three of the generated transgenic hairy root lines were found to accumulate novel molecules, two of which were shown to be novel triterpene saponins, whereas the third line produced a set of novel, non-saponin compounds. Furthermore, the identified transcription factors and other regulators were lead candidates for studies investigating the control of the saponin biosynthesis in planta. This led to the identification of a RING membrane-anchor E3 ubiquitin ligase, MAKIBISHI1 (MKB1), that targets 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), the enzyme catalyzing the rate-limiting step in the mevalonate pathway, for ubiquitin-mediated proteasomal degradation, thereby controlling saponin biosynthesis.},
  author       = {Pollier, Jacob},
  keyword      = {Transcript Profiling,Triterpene Saponins,Combinatorial Biochemistry,Natural Products,Secondary Metabolites,Metabolite Profiling},
  language     = {eng},
  pages        = {VIII, 223},
  publisher    = {Ghent University. Faculty of Sciences},
  school       = {Ghent University},
  title        = {Combinatorial biochemistry of triterpene saponins in plants},
  year         = {2011},
}