Genome Reveals Reasons for Marijuana's Mind-altering Properties

Marijuana (Cannabis sativa) is a famous plant because of its mind-altering properties and medicinal value for more than 2700 years. It's been a mystery to scientists how cannabis evolved to become a drug-producing plant. A change in the genome that caused this evolution was discovered by a team of scientists led by Jon Page and Tim Hughes from Canada. They sequenced the DNA of the potent Purple Kush (PK) marijuana strain, which is extensively used for medicinal purposes. They compared the genome and the turned-on genes of PK and ‘Finola' hemp, and searched for differences that might explain why marijuana produces tetrahydrocannabinolic acid (THCA), the active ingredient of cannabis, while hemp strains lack THCA but contain the non-psychoactive cannabinoid, cannabidiolic acid (CBDA).

They got the clues from the analysis of the turned-on genes (transciptome analysis) which showed that the THCA gene is turned on in marijuana but turned off in hemp. Detailed genome analysis also showed that domestication, cultivation, and breeding of marijuana strains have caused the loss of an enzyme which would otherwise compete for the metabolites used as starting material in THCA production.

"Plants continue to be a major source of medicines, both as herbal drugs and as pharmaceutical compounds. Although more than twenty plant genomes have been published, ranging from major food crops such as rice and corn, to laboratory models like Arabidopsis, this is the first genome of a medicinal plant. Decoding the cannabis genome will help answer basic questions about the biology of Cannabis sativa and further the development of its myriad applications including strains for pharmaceutical production, and hemp plants with improved productivity and fatty acid profiles," explained Page.

Read more at http://genomebiology.com/2011/12/10/409.