Engineering linear, branched-chain triterpene metabolism in monocots

Chase Kempinski, Zuodong Jiang, Garrett Zinck, Shirley J. Sato, Zhengxiang Ge, Thomas E. Clemente, Joe Chappell

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Triterpenes are thirty-carbon compounds derived from the universal five-carbon prenyl precursors isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). Normally, triterpenes are synthesized via the mevalonate (MVA) pathway operating in the cytoplasm of eukaryotes where DMAPP is condensed with two IPPs to yield farnesyl diphosphate (FPP), catalyzed by FPP synthase (FPS). Squalene synthase (SQS) condenses two molecules of FPP to generate the symmetrical product squalene, the first committed precursor to sterols and most other triterpenes. In the green algae Botryococcus braunii, two FPP molecules can also be condensed in an asymmetric manner yielding the more highly branched triterpene, botryococcene. Botryococcene is an attractive molecule because of its potential as a biofuel and petrochemical feedstock. Because B. braunii, the only native host for botryococcene biosynthesis, is difficult to grow, there have been efforts to move botryococcene biosynthesis into organisms more amenable to large-scale production. Here, we report the genetic engineering of the model monocot, Brachypodium distachyon, for botryococcene biosynthesis and accumulation. A subcellular targeting strategy was used, directing the enzymes (botryococcene synthase [BS] and FPS) to either the cytosol or the plastid. High titres of botryococcene (>1 mg/g FW in T 0 mature plants) were obtained using the cytosolic-targeting strategy. Plastid-targeted BS + FPS lines accumulated botryococcene (albeit in lesser amounts than the cytosolic BS + FPS lines), but they showed a detrimental phenotype dependent on plastid-targeted FPS, and could not proliferate and survive to set seed under phototrophic conditions. These results highlight intriguing differences in isoprenoid metabolism between dicots and monocots.

Original languageEnglish
Pages (from-to)373-385
Number of pages13
JournalPlant Biotechnology Journal
Volume17
Issue number2
DOIs
StatePublished - Feb 1 2019

Bibliographical note

Funding Information:
We acknowledge the help of all Chappell lab members past and present, with special help from Stephen Bell for vector design, Scott Kinison, and Kristin Linscott for help in the yeast evaluation studies. This work was supported by grant 201006141622 from the National Institute of Food and Agriculture – USDA.

Publisher Copyright:
© 2018 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.

Keywords

  • Brachypodium
  • Sorghum
  • botryococcene
  • metabolic engineering
  • monocot
  • triterpene

ASJC Scopus subject areas

  • Biotechnology
  • Agronomy and Crop Science
  • Plant Science

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