27) The Origin of Cannabis Revealed by Genetic Analysis

The Origin of Cannabis Revealed by Genetic Analysis

Marijuana users have often wondered about the origins of their beloved—but also heavily criticized—plant. Now, they no longer need to question it: new genetic research reveals that cannabis traces its roots back to what is now northwest China, where local varieties closely resemble the original strain of cannabis cultivated over 12,000 years ago.

The study - the largest ever conducted on the complete genomes of cannabis plants, adding 82 more genomes to the 28 that had already been sequenced - shows that cannabis was likely first domesticated in the early Neolithic period in the region of modern China, near its borders with Kazakhstan and Kyrgyzstan, and from there spread in different varieties around the world.

Researchers have identified a "basal type" of cannabis plant from northwest China that was previously unknown, Luca Fumagalli, a geneticist at the University of Lausanne in Switzerland, told Live Science.

As cannabis plants are now widespread, there has been considerable scientific debate about their origin, and suggestions have included West Asia, Central Asia and northern China, Fumagalli said.

" People thought the region was more toward Central Asia, mainly because there were a lot of wild cannabis plants along the roads there," he said. "But those observational data actually contradicted what we got from the genomic analysis."

Instead, the study showed that the Central Asian cannabis plants were of the “hemp type,” he said, meaning they are tall, unbranched, with cellulose-rich stems, suited to producing fiber for ropes and textiles. They were not of the basal type, which is suited to both fiber production and psychoactive effects.

One Species Only

Most biologists now believe that two different species of Cannabis - Cannabis indica and Cannabis ruderalis - are subspecies of the single species in the genus, Cannabis sativa, which was domesticated about 12,000 years ago.

This dating is supported by archaeological evidence, which includes traces of ancient cannabis seeds found in pottery from this period in southern China, Taiwan and Japan.

Fumagalli said the genetic study led researchers to conclude that all cannabis plants alive today are descended from plants domesticated in the region of origin, and that the wild ancestors of Cannabis sativa are likely now extinct.

The different types of cannabis would have started to diverge from the basal type after its domestication, and the study showed that the hemp type became predominant about 4,000 years ago, likely when people began breeding the plants for fiber production, he said.

Hemp-type varieties of cannabis now grow wild throughout Europe, Central Asia and parts of northern China. Cannabis varieties grown commercially for drugs come exclusively from the drug type, which has been selected for the high levels of psychoactive chemicals it produces; and wild drug-type varieties now grow wild throughout South and Southeast Asia, where cannabis appears to have been cultivated over the last few thousand years, primarily for the psychoactive effects of marijuana, he said.

Highlights

The four types of cannabis differ primarily in the gene assemblies that control their production of two particular acidic cannabinoids – CBDA, which produces the chemical CBD and is predominant in the hemp-type variety, and THCA, which produces the more psychoactive chemical THC.

In the plant, CBDA and THCA are produced and compete for the same raw material, cannabigerolic acid, or CBGA. Scientists believe that both sets of genes likely play a major role in the plant’s defenses. However, the genes produced very different effects on the cultivation of each type of plant, with the hemp type favoring the production of the CBDA gene construct and the drug type favoring the THCA gene construct, the researchers wrote.

They noted that cannabis has long been considered an important source of fiber for textiles as well as a source of medicines and recreational drugs, but the history of its domestication has been difficult to determine - due to legal restrictions and clandestine breeding for drugs

That is beginning to change, however. "Our study provides new insights into the global spread of a plant with divergent structural and biochemical products, at a time when there is renewed interest in its use, reflecting changing social attitudes and corresponding challenges to its legal status in many countries," the researchers wrote.

The new genetic research is intended to serve as a resource for medical and agricultural research on cannabis. "East Asia has been shown to be an important ancient hotspot of domestication for several crop species, including rice, foxtail and cluster millet, soybean, foxtail, apricot, and peach. … Our results therefore add another line of evidence for the importance of this domestication hotspot."

The study was published Friday, July 16, in the journal Science Advances.

Initialement publié sur Live Science. HERE