On the Origin of Cannabis

A growing number of researchers continue to dig into the effects of cannabis – medical or otherwise – but less attention has been paid to how the plant came by its distinctive chemical composition. Now, having published the world’s first cannabis genome map, researchers suggest that the secret to THC and CBD synthesis may be down to colonization of the plant’s genome by viruses millions of years ago (1).

According to Harm van Bakel, one of the researchers based at the Icahn School of Medicine at Mount Sinai in New York, plant genomes can contain millions of retroelement (viral DNA) copies, which makes it difficult to link genes on chromosomes – “analogous to assembling a huge puzzle where three quarters of the pieces are nearly the same color.” But by combining a genetic map and PacBio sequencing, the team was able to locate distinct THCA and CBDA synthase genes. The team believes that their genetic similarity (but distinct location) indicates that they are duplicates of the same gene that were subsequently “scrambled” by invading retroelements before evolving independently.

The researchers also identified the gene responsible for the synthesis of CBC – a cannabinoid that fails to gain the limelight but nevertheless appears to have interesting pharmacological properties.

Beyond evolutionary intrigue, Tim Hughes, a professor in the Donnelly Centre for Cellular and Biomolecular Research at the University of Toronto and co-leader of the study, explained the wider relevance of the work: “The chromosome map is an important foundational resource for further research which, despite cannabis’ widespread use, has lagged behind other crops due to restrictive legislation.”

Indeed, armed with the cannabis genome map and with newfound confidence that THC and CBD (and CBC!) are all produced by distinct enzymes, the cannabis community may be able to better tailor the respective content of each compound during selective breeding – a process that has confounded breeders in the past.