In December 2020, the New Phytologist published a comprehensive research review exploring recent advances in cannabis genomics. Despite so many historical barriers, researchers are finally investigating the fascinating genetic makeup of cannabis.
The following is the Coles Notes version of their findings.
What Has Historically Hampered Cannabis Genome Work?
Until recently, it has been essentially impossible for researchers to explore and sequence the cannabis genome. Despite growing global legalization, there are still significant barriers. One of the most notable for international cooperation is the restrictions on shipping and the exchange of cannabis genetic resources across international borders.
It is a prolonged process to change international drug scheduling based on the tedious decision-making process by the likes of the World Health Organization (WHO), the United Nations (UN), and the European Union.
Another barrier researchers face in the field of cannabis genomics is the casual and inaccurate strain-name game. According to the authors of this 2020 research review, cannabis is routinely classified incorrectly. Across the industry, breeders, cultivators, and retailers still fail to classify strains correctly.
Hurgobin, Tamiru-Oli, et al. also describe how “intensive clandestine breeding practices since the early 1970s have led to a genetic bottleneck and reduced allelic diversity in marijuana plants.” This means cannabis today is remarkably less genetically diverse than in decades past. Tracing back the evolution of certain genetic traits is difficult because much of this evidence no longer exists.
Advances in Cannabis Genomics
Despite these setbacks, the world of cannabis genetics is evolving. The combination of cannabis-friendly legislation and rapidly advancing genomics techniques have helped researchers uncover some of the mysteries surrounding this plant's genetic makeup. Over the last decade, there have been some big wins for cannabis genomics.
According to the authors, “Large-scale gene expression studies on cannabis have been instrumental in elucidating cannabinoid metabolism.” Thus far, researchers have determined that many different enzymes within cannabis are responsible for transforming cannabinoids from the mother cannabinoid — cannabigerol (CBG) — into the many final forms like tetrahydrocannabinolic acid (THCa) and cannabidiolic acid (CBDa).
Additional studies have also discovered exponentially more cannabinoid genetic pathways in medicinal strains (Purple Kush) compared with hemp cultivars (Finola). Which would make sense, considering most medicinal strains contain substantially higher levels of cannabinoids when compared with hemp. New sequencing has also compared male and female plants and begun to dig into genes responsible for terpene expression.
Cannabinoid Content in Relation to Copy Number Variations
Copy number variations, or CNVs, are structural variations between two genomes. CNVs are essentially a section of the genome which is repeated, and the number of repetition may differ between individuals.
Thus far, the CNVs are more common for CBDa-related genes and less so for THCa genes. Another interesting finding of cannabis CNVs is that the number of CNVs may not be related to the end cannabinoid content. As in, more copies of CBDa may not mean more CBDa. This is an ongoing area of research, however, and much remains unclear. However, it seems probable that the stabilization of genetics will likely result in higher cannabinoid yields.
As the authors note, “Despite their therapeutic potential and similar biosynthetic origin, genetic prediction of terpene composition is challenging.” A few studies have hinted that gene duplication events and gene clusters may have something to do with terpene profile. Still, this area of research is far from being able to predict the final terpene profile of any given cultivar.
Many factors influence cannabis' terpene expression, like cultivar, tissue type, trichome morphotypes, developmental stage, and even oxidization. Researchers have a long road ahead before confidently predicting the final expression of terpenes.
The Evolutionary History of the Cannabis Genome
A method known as high-throughput SNP has proven quite helpful for the study of the cannabis genome. We now understand much more about the mysterious nature of this plant's evolution.
For starters, we now know that the differences between hemp and drug-type cultivars have resulted explicitly from selective breeding. Another discovery? That there have been many errors in classification thanks to poorly recorded and/or understood breeding programs.
Understanding of the Cannabis Genome Supports the Evolution of the Cannabis Sector
Understanding the cannabis genome means the continued evolution of both the industry's medicinal and recreational markets. These advances will lead to accurate cultivar identification for both breeders and consumers, as well as help trackability and traceability.
Importantly, this vital cannabis genomics work will also lead to more intentional breeding programs to improve the genetic diversity of this remarkable plant. The end goal would be to better predict cannabinoid and terpene expression for more predictable medicinal and recreational applications.