University of Minnesota researchers have identified genes producing tetrahydrocannabinol (THC), the psychoactive substance in marijuana, in a first step toward engineering a drug-free Cannabis plant for hemp fiber and oil.
Studying the genes may also lead to new and better drugs for pain, nausea, and other conditions. The finding was published in an issue of the Journal of Experimental Botany and lead author was David Marks, a professor of plant biology in the College of Biological Sciences.
The genes are active in tiny hairs covering the flowers of cannabis plants, the study revealed. It was revealed that the hairs accumulate high amounts of THC in marijuana, whereas the hairs have little amounts of THC in hemp. With the genes identified, the dream of producing a drug-free plant can now be a reality. This can be accomplished by engineering a hairless Cannabis plant since the hairs can be seen with a magnifying glass.
“We are beginning to understand which genes control hair growth in other plants, and the resources created in our study will allow us to look for similar genes in Cannabis sativa,” said Marks.
“Cannabis genetics can contribute to better agriculture, medicine, and drug enforcement,” said George Weiblen, an associate professor of plant biology and a co-author of the study.
“I can’t think of a plant so regarded as a menace by some and a miracle by others,” says Weiblen, who is one of the few researchers in the United States permitted to study Cannabis genetics. In 2006, Weiblen and colleagues developed a DNA “fingerprinting” technique capable of distinguishing among Cannabis plants in criminal investigations.
Identification of candidate genes affecting Δ9-tetrahydrocannabinol biosynthesis in Cannabis sativa
M. David Marks1,*, Li Tian2,†, Jonathan P. Wenger1, Stephanie N. Omburo1, Wilfredo Soto-Fuentes1, Ji He2, David R. Gang3, George D. Weiblen1 and Richard A. Dixon2
RNA isolated from the glands of a Δ9-tetrahydrocannabinolic acid (THCA)-producing strain of Cannabis sativa was used to generate a cDNA library containing over 100 000 expressed sequence tags (ESTs). Sequencing of over 2000 clones from the library resulted in the identification of over 1000 unigenes. Candidate genes for almost every step in the biochemical pathways leading from primary metabolites to THCA were identified. Quantitative PCR analysis suggested that many of the pathway genes are preferentially expressed in the glands. Hexanoyl-CoA, one of the metabolites required for THCA synthesis, could be made via either de novo fatty acids synthesis or via the breakdown of existing lipids. qPCR analysis supported the de novo pathway. Many of the ESTs encode transcription factors and two putative MYB genes were identified that were preferentially expressed in glands. Given the similarity of the Cannabis MYB genes to those in other species with known functions, these Cannabis MYBs may play roles in regulating gland development and THCA synthesis. Three candidates for the polyketide synthase (PKS) gene responsible for the first committed step in the pathway to THCA were characterized in more detail. One of these was identical to a previously reported chalcone synthase (CHS) and was found to have CHS activity. All three could use malonyl-CoA and hexanoyl-CoA as substrates, including the CHS, but reaction conditions were not identified that allowed for the production of olivetolic acid (the proposed product of the PKS activity needed for THCA synthesis). One of the PKS candidates was highly and specifically expressed in glands (relative to whole leaves) and, on the basis of these expression data, it is proposed to be the most likely PKS responsible for olivetolic acid synthesis in Cannabis glands.
University of Minnesota (2009, September 15). Hemp And Marijuana: Genes Producing THC