THCA synthase (THCAS) is an oxidocyclase enzyme that closes a ring in CBGA to form THCA. It is made in the secretory cells of glandular trichomes and works in the storage cavity under the resin head. Sirikantaramas and colleagues cloned and expressed the gene in 2004, confirming it as the gene behind THCA production.
In practice
Breeders treat the synthase region as the main switch for chemotype. A plant with functional THCAS alleles and non-functional CBDAS makes mostly THCA; one with functional CBDAS and non-functional THCAS makes mostly CBDA; one with one of each tends toward a mixed profile. Genotyping tests can read these alleles in seedlings, telling a breeder the likely THC:CBD class long before flowering. They cannot predict the total percentage: that depends on many other genes, trichome density and growing conditions.
Don't confuse with
- CBDA synthase: the competing enzyme that makes CBDA from the same CBGA.
- THC: the neutral product formed later by decarboxylation, not by the enzyme.
- Potency: THCAS sets the type of cannabinoid, not how much.
CBGA (cannabigerolic acid) is the precursor cannabinoid that the plant converts into THCA, CBDA or CBCA, formed by joining olivetolic acid to geranyl pyrophosphate.THCA (tetrahydrocannabinolic acid) is the acid cannabinoid that drug-type cannabis makes in its trichomes; heat or time decarboxylates it into THC, losing about 12% of its mass.A gene is a stretch of DNA that carries the instructions for one functional product, usually a protein such as an enzyme, and is the basic unit of inheritance.An allele is one version of a gene; a diploid cannabis plant carries two alleles at each locus, one from each parent, which may be the same or different.CBDA synthase is the trichome enzyme that converts CBGA into CBDA; it competes with THCA synthase, and its alleles largely decide whether a plant is CBD-dominant.CBDA (cannabidiolic acid) is the acid cannabinoid made by CBDA synthase from CBGA; it dominates hemp-type and CBD-type cannabis and decarboxylates to CBD.THC (Δ9-tetrahydrocannabinol) is the neutral, decarboxylated cannabinoid mainly responsible for cannabis's reported intoxicating effects; the living plant makes it almost entirely as THCA.CBD (cannabidiol) is a non-intoxicating neutral cannabinoid formed when CBDA decarboxylates; hemp-type and CBD-dominant cannabis make it mainly as CBDA in their trichomes.The chemotype ratio is the balance of a plant's main cannabinoids, usually THC to CBD, classing plants as type I (THC-dominant), II (mixed), III (CBD-dominant), IV (CBG) or V (near-zero).A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA.
