title: Laticifer-specific cis-prenyltransferase silencing affects the rubber, triterpene, and inulin content of Taraxacum brevicorniculatum.
abstract: Certain Taraxacum species, such as Taraxacum koksaghyz and Taraxacum brevicorniculatum, produce large amounts of high-quality natural rubber in their latex, the milky cytoplasm of specialized cells known as laticifers. This high-molecular mass biopolymer consists mainly of poly(cis-1,4-isoprene) and is deposited in rubber particles by particle-bound enzymes that carry out the stereospecific condensation of isopentenyl diphosphate units. The polymer configuration suggests that the chain-elongating enzyme (rubber transferase; EC 2.5.1.20) is a cis-prenyltransferase (CPT). Here, we present a comprehensive analysis of transgenic T. brevicorniculatum plants in which the expression of three recently isolated CPTs known to be associated with rubber particles (TbCPT1 to -3) was heavily depleted by laticifer-specific RNA interference (RNAi). Analysis of the CPT-RNAi plants by nuclear magnetic resonance, size-exclusion chromatography, and gas chromatography-mass spectrometry indicated a significant reduction in rubber biosynthesis and a corresponding 50% increase in the levels of triterpenes and the main storage carbohydrate, inulin. Transmission electron microscopy revealed that the laticifers in CPT-RNAi plants contained fewer and smaller rubber particles than wild-type laticifers. We also observed lower activity of hydroxymethylglutaryl-coenzyme A reductase, the key enzyme in the mevalonate pathway, reflecting homeostatic control of the isopentenyl diphosphate pool. To our knowledge, this is the first in planta demonstration of latex-specific CPT activity in rubber biosynthesis.
authors.affiliation: Westphalian Wilhelms-University of Münster, Institute of Plant Biology and Biotechnology, 48143 Munster, Germany.
authors.forename: Janina
authors.initials: J
authors.lastname: Post
authors.forename: Nicole
authors.initials: N
authors.lastname: van Deenen
authors.forename: Julia
authors.initials: J
authors.lastname: Fricke
authors.forename: Natalie
authors.initials: N
authors.lastname: Kowalski
authors.forename: David
authors.initials: D
authors.lastname: Wurbs
authors.forename: Hubert
authors.initials: H
authors.lastname: Schaller
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Eisenreich
authors.forename: Claudia
authors.initials: C
authors.lastname: Huber
authors.forename: Richard M
authors.initials: RM
authors.lastname: Twyman
authors.forename: Dirk
authors.initials: D
authors.lastname: Prüfer
authors.forename: Christian Schulze
authors.initials: CS
authors.lastname: Gronover
mesh_terms: D002850:Chromatography, Gel; D008401:Gas Chromatography-Mass Spectrometry; D045782:Hemiterpenes / Q000737:chemistry; D006706:Homeostasis; D006903:Hydroxymethylglutaryl CoA Reductases / Q000737:chemistry; D007444:Inulin / Q000737:chemistry*; D007840:Latex / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D046529:Microscopy, Electron, Transmission; D009943:Organophosphorus Compounds / Q000737:chemistry; D018517:Plant Roots / Q000737:chemistry / Q000201:enzymology / Q000648:ultrastructure; D030821:Plants, Genetically Modified / Q000737:chemistry / Q000201:enzymology; D034622:RNA Interference; D012408:Rubber / Q000737:chemistry*; D031205:Taraxacum / Q000737:chemistry* / Q000201:enzymology; D014166:Transferases / Q000737:chemistry*; D019076:Transgenes; D014315:Triterpenes / Q000737:chemistry*
chemical_list: D045782:Hemiterpenes; D007840:Latex; D009943:Organophosphorus Compounds; D014315:Triterpenes; C004809:isopentenyl pyrophosphate; C455100:1,4-polyisoprene; D007444:Inulin; D012408:Rubber; D006903:Hydroxymethylglutaryl CoA Reductases; D014166:Transferases; C106821:cis-prenyl transferase