title: Development of rubber-enriched dandelion varieties by metabolic engineering of the inulin pathway.
abstract: Natural rubber (NR) is an important raw material for a large number of industrial products. The primary source of NR is the rubber tree Hevea brasiliensis, but increased worldwide demand means that alternative sustainable sources are urgently required. The Russian dandelion (Taraxacum koksaghyz Rodin) is such an alternative because large amounts of NR are produced in its root system. However, rubber biosynthesis must be improved to develop T. koksaghyz into a commercially feasible crop. In addition to NR, T. koksaghyz also produces large amounts of the reserve carbohydrate inulin, which is stored in parenchymal root cell vacuoles near the phloem, adjacent to apoplastically separated laticifers. In contrast to NR, which accumulates throughout the year even during dormancy, inulin is synthesized during the summer and is degraded from the autumn onwards when root tissues undergo a sink-to-source transition. We carried out a comprehensive analysis of inulin and NR metabolism in T. koksaghyz and its close relative T. brevicorniculatum and functionally characterized the key enzyme fructan 1-exohydrolase (1-FEH), which catalyses the degradation of inulin to fructose and sucrose. The constitutive overexpression of Tk1-FEH almost doubled the rubber content in the roots of two dandelion species without any trade-offs in terms of plant fitness. To our knowledge, this is the first study showing that energy supplied by the reserve carbohydrate inulin can be used to promote the synthesis of NR in dandelions, providing a basis for the breeding of rubber-enriched varieties for industrial rubber production.
authors.affiliation: Institute of Plant Biology and Biotechnology, University of Muenster, Muenster, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Stolze
authors.affiliation: Institute of Plant Biology and Biotechnology, University of Muenster, Muenster, Germany.
authors.forename: Alan
authors.initials: A
authors.lastname: Wanke
authors.affiliation: Institute of Plant Biology and Biotechnology, University of Muenster, Muenster, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: van Deenen
authors.affiliation: numares AG, Regensburg, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Geyer
authors.affiliation: Institute of Plant Biology and Biotechnology, University of Muenster, Muenster, Germany.|Fraunhofer Institute for Molecular Biology and Applied Ecology (IME), Muenster, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Prüfer
authors.affiliation: Fraunhofer Institute for Molecular Biology and Applied Ecology (IME), Muenster, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schulze Gronover
mesh_terms: D018506:Gene Expression Regulation, Plant; D007444:Inulin / Q000378:metabolism*; D060847:Metabolic Engineering / Q000379:methods*; D018517:Plant Roots / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism*; D031205:Taraxacum / Q000235:genetics / Q000378:metabolism*; D014315:Triterpenes / Q000378:metabolism
chemical_list: D014315:Triterpenes; D007444:Inulin
keywords: 
  Taraxacum koksaghyz
  ; fructan 1-exohydrolase; fructosyltransferase; inulin; natural rubber; triterpene