THC and CBD may have been created by a virus

The study, published in the journal Genome Research, is the result of a three-way collaboration between researchers at Aurora Cannabis, the University of British Columbia, and the Mount Sinai School of Medicine in New York. The map details the arrangement of genes on the plant’s chromosomes. This has made it possible to learn more about the past genetic evolution of cannabis, with the goal of guiding its future evolution to adapt it to the needs of the industry and patients.

The Past Genetic Evolution of Cannabis

THC and CBD originated from an ancient virus

The two best-known active ingredients in cannabis—and the ones around which the industry has been built—are THC and CBD. Genetic research on the plant shows that these molecules are the result of a viral infection that occurred millions of years ago. This infection is believed to have permanently altered the plant’s DNA and created the enzymes CBDA and THCA, which, through decarboxylation, provide the THC and the CBD.

THCA and CBDA are located on chromosome 6 of the 10 chromosomes that make up the Cannabis sativa genome. They are surrounded by bands of denatured DNA that indicate viral activity. When a virus enters the organism, its DNA replicates itself repeatedly within healthy DNA cells, spreading throughout the genome. These copies are called retroelements; their presence around the genes that produce THCA and CBDA suggests that these enzymes are the result of a mutation caused by the virus.

THC and CBD are independent of each other

Although the THCA and CBDA enzymes are located on the same chromosome, they are not encoded by the same gene. The genetic sequences of the two enzymes are, however, nearly identical. This DNA similarity suggests that they originally came from the same gene but evolved separately to create two varieties with distinct chemical properties from the same species: CBD-rich hemp and THC-rich «marijuana.» This separation was subsequently exacerbated by human-induced genetic manipulation.

Nevertheless, both hemp and marijuana contain both THC and CBD. Thus, it was unclear whether the two enzymes originated from two different genes or from two versions of the same gene. The map clearly shows that they are encoded in two different genes. It would therefore be technically possible to grow THC-free hemp varieties and, conversely, «marijuana» varieties without CBD. In fact, another study revealed that genetic manipulation aimed at achieving high THC concentrations resulted in underdevelopment of CBD, suggesting that the pursuit of THC was coming at the expense of CBD content.

The Future Genetic Evolution of Cannabis

What can we do with this discovery? This new genetic knowledge could, in fact, make it possible to create varieties that are more resistant to certain diseases or insects. It will also guide the breeders in their development by allowing them to control the levels of certain cannabinoids and achieve the desired medicinal effects. For example, the map also led to the discovery of the gene responsible for a lesser-known but equally interesting cannabinoid: the cannabichromene (CBC). Some of the psychoactive effects of cannabis are thought to be attributable to this cannabinoid, which is believed to activate THC. In addition, it possesses anti-inflammatory properties that are of interest to pharmacology. The discovery of this gene may make it possible to control the concentration of CBC in future cannabis strains.

This is the first time such a detailed map of the plant’s genome has been developed. A preliminary version was published in 2011 by the same researchers, but the difficulty of incorporating cannabis into research hindered the development of this type of study. Public funding was also ruled out due to the raw materials required. «Science hasn’t advanced much so far because of restrictions on research,» explains Aurora’s chief scientific officer, Jonathan Page. «Legalization and the easing of research regulations are creating opportunities for more studies. And Canada is leading the way.».