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Crop Biotech Update

Scientists Closer to Drug-Free Cannabis Plants

September 18, 2009

Researchers are closing in on developing drug-free Cannabis plants. A team of scientists from the University of Minnesota have identified almost all the genes involved in the biosynthetic pathway tetrahydrocannabinolic acid (THCA), the psychoactive substance in marijuana. With the genes identified, the scientists can now devise ways to silence them, for instance using RNA interference. The researchers said that studying these genes can also lead to new drugs for pain and nausea.

David Marks and colleagues, reporting in the Journal of Experimental Botany, found that the genes are highly expressed in tiny hairs covering the flowers of Cannabis plants. The researchers have identified specific polyketide synthase genes that are highly expressed in the hairs. In marijuana, the hairs accumulate high amounts of THCA, whereas in hemp the hairs have little (marijuana and hemp are different breeds of Cannabis sativa).

Hemp varieties have THCA levels at or below 0.3 percent, while the average THCA content of marijuana can reach 30 percent. Hemp has once been a popular crop, an important source of strong, industrial fiber and nutritious oil. But after the drug legislation, its cultivation was banned because of the fear that hemp planting could mask the growth of marijuana.

The findings may also prove important to the beer industry. According to the researchers, the polyketide synthase genes identified in cannabis plants are closely related to those from hop. Hop plants produce humulone, the bitter compound that gives beer its distinctive taste, and xanthohumol, which has several potential health beneficial properties. The biosynthetic pathways that produce these compounds are almost identical to the THCA pathway, according to the scientists. Thus, studying the Cannabis genes might provide information for improved understanding of hop biochemical pathways.

The open access article is available at http://dx.doi.org/10.1093/jxb/erp210