Engineering linear, branched-chain triterpene metabolism in monocots.

Area of Science:

• Biochemistry
• Metabolic Engineering
• Plant Science

Background:

• Triterpenes, like botryococcene, are synthesized from prenyl precursors via the mevalonate pathway.
• Botryococcene is a valuable compound for biofuels and petrochemicals.
• Botryococcus braunii, the natural producer, is challenging for large-scale cultivation.

Purpose of the Study:

• To genetically engineer the model monocot Brachypodium distachyon for botryococcene biosynthesis.
• To investigate the impact of subcellular enzyme targeting (cytosolic vs. plastid) on botryococcene production and plant phenotype.

Main Methods:

• Genetic engineering of Brachypodium distachyon to express botryococcene synthase (BS) and farnesyl diphosphate synthase (FPS).
• Subcellular targeting strategies were employed to direct enzymes to the cytosol or plastids.
• Quantification of botryococcene accumulation and assessment of plant phenotypes.

Main Results:

• High titres of botryococcene (>1 mg/g FW) were achieved in T0 mature plants using cytosolic-targeted enzymes.
• Plastid-targeted enzymes led to lower botryococcene accumulation.
• Plastid targeting of FPS resulted in detrimental plant phenotypes, preventing seed set.

Conclusions:

• Successful engineering of botryococcene biosynthesis in Brachypodium distachyon.
• Cytosolic targeting is an effective strategy for high-yield botryococcene production in monocots.
• Significant differences in isoprenoid metabolism exist between monocots and dicots, impacting engineered pathways.