Polarized supercell produces specialized metabolites in cannabis trichomes

Researchers identify high-efficiency mechanisms used by cannabis cells to make cannabinoids

For the first time, biologists have defined the high-yield "tricks" that cannabis cells use to make cannabinoids (THC/CBD). Although many biotech companies are currently trying to make THC/CBD outside of the plant, in yeast or cell cultures, it is still unclear how the plant does this naturally.

For centuries, humans have cultivated cannabis for the pharmacological properties that result from the consumption of its specialized metabolites, primarily cannabinoids and terpenoids. Today, cannabis is a multi-billion dollar industry whose existence relies on the biological activity of tiny cell clusters, called glandular trichomes, found primarily on flowers.

Cannabis glandular trichomes alter morphology and metabolite content during flower maturation

Cannabinoids are toxic to cannabis cells, and it is not known how the cells of cannabis trichomes can produce and secrete massive amounts lipophilic metabolites. To address this knowledge gap, we studied cannabis glandular trichomes using ultra-rapid cryofixation, quantitative electron microscopy, and gold labeling of cannabinoid pathway enzymes.

Study demonstrates that metabolically active Cannabis cells form a 'supercell', with extensive cytoplasmic bridges across cell walls and a polar distribution of organelles adjacent to the apical surface where the metabolites are secreted. The predicted metabolic role of non-photosynthetic plastids is supported by unusual membrane networks in plastids and the location of the start of the cannabinoid/terpene pathway in the plastid stroma. Abundant membrane contact sites link the paracrystalline nuclei of the plastids to the plastid envelope, the plastids to the endoplasmic reticulum (ER), and the ER to the plasma membrane.

The final step in cannabinoid biosynthesis, catalyzed by tetrahydrocannabinolic acid synthase (THCAS), was localized in the cell surface wall, opposite the extracellular storage cavity. We propose a novel model of how cannabis cells can sustain abundant metabolite production, emphasizing the key role of membrane contact sites and extracellular THCA biosynthesis. This new model may inform synthetic biology approaches for cannabinoid production in yeast or cell cultures.

“It really helps us understand how cannabis trichome cells can produce massive amounts of tetrahydrocannabinol (THC) and terpenes – compounds that are toxic to plant cells in large quantities – without poisoning themselves. said Dr. Sam Livingston, a botanist at the University of British Columbia, who led the research.

For decades, humans have cultivated cannabis for the pharmacological properties that result from the consumption of its specialized metabolites, primarily CBD and terpenoids. Today, the production of the $20 billion global cannabis market relies heavily on the biological activity of tiny clumps of cells, called glandular trichomes, found primarily on the flowers of the plant. .

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The study, published in Current Biology, reveals the microenvironments in which THC is produced and transported in cannabis trichomes, and sheds light on several critical points in the pathway of THC or CBD manufacturing within the cell.

Dr. Livingston and co-author Dr. Lacey Samuels used rapid freezing of cannabis glandular trichomes to immobilize plant cellular structures and metabolites in situ. They were thus able to study the glandular trichomes of cannabis using electron microscopes which revealed the cellular structure at the nanoscale, showing that the metabolically active cells of cannabis form a "supercell" which acts as a tiny metabolic biofactory.

Until now, synthetic biology approaches have focused on optimizing the enzymes responsible for making THC/CBD – like building a factory with the most efficient machinery to make as many products as possible. . However, these approaches have not developed an efficient way to move intermediate substances from one enzyme to another, or from inside the cell to outside the cell where the end products can be collected. This research helps define the subcellular "shipping routes" that cannabis uses to create an efficient pipeline from raw materials to final products without accumulating toxins or waste.

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“For more than 40 years, everything we thought about cannabis cells was inaccurate because it was based on dated electron microscopy,” says Dr. Samuels, plant cell biologist at UBC. “This work defines how cannabis cells make their product. This is a paradigm shift after many years, producing a new vision of cannabinoid production. This work has been difficult, partly because of the legal prohibition and also because no cannabis genetic transformation protocol has been published. »

Today we know that:

  • Glandular cells form a polarized syncytium during the production and secretion of THCA.
  • GPPS is localized in plastids that contain conspicuous membrane fusions.
  • THCAS is localized exclusively on the extracellular surface of trichomes.
  • Membrane contacts between plastids, ER and PM are at the origin of a new traffic pattern.

This new model may inform synthetic biology approaches for cannabinoid production in yeast, which is commonly used in biotechnology. Without these “hacks”, they will never achieve efficient production.

Tags : GeneticSEARCHsyntheticterpenetrichome

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