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Laticifer-specific cis-prenyltransferase silencing affects the rubber, triterpene, and inulin content of Taraxacum brevicorniculatum

 
: Post, J.; Deenen, N. van; Fricke, J.; Kowalski, N.; Wurbs, D.; Schaller, H.; Eisenreich, W.; Huber, C.; Twyman, R.M.; Prüfer, D.; Gronover, C.S.

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Plant Physiology 158 (2012), No.3, pp.1406-1417
ISSN: 0032-0889
English
Journal Article
Fraunhofer IME ()

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 indi cated 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.

: http://publica.fraunhofer.de/documents/N-206852.html