The past few months has yielded a bountiful crop of genome sequence from the first medicinal plant to be sequenced: Cannabis sativa.

In August, a new company called Medicinal Genomics released the raw sequence of the C. sativa genome. Today, a group of Canadian researchers published the draft genome and a survey of gene expression in Purple Kush, a strain that they say (I’ll take their word for it) is particularly potent. (For those keeping track, Medicinal Genomics sequenced the ‘Chemdawg’ strain.)

This time, tiny fragments of genome sequence have been stitched together into big chunks, enabling a more thorough analysis of its contents. The team, lead by Timothy Hughes of the University of Toronto and Jonathan Page of the University of Saskatchewan, also compared Purple Kush to the hemp cultivars ‘Finola’ and ‘USO-31’, and found that a key enzyme in the cannabinoid biosynthetic pathway –- Δ9-tetrahydrocannabinolic acid synthase –- is expressed in Purple Kush but not in the hemp strains. That difference, reported along with the genome sequence today in Genome Biology, could account for why hemp does not make an appreciable amount of that most revered of all cannabinoids, the psychoactive THC.

What brought about this change in expression? We’d probably already know that, said the authors, if it weren’t for the “severe legal restrictions in most jurisdictions on growing cannabis, even for research purposes”. But they’re optimistic that comparative genomics — performed in silico — will teach them more about what regulates gene expression in Purple Kush, and perhaps pave the way to finer tailoring of cannabinoid content in new strains of marijuana.

Image: warrantedarrest, Flickr, creative commons.