# THCA synthase

> THCA synthase is the trichome enzyme that converts CBGA into THCA; which alleles of its gene a plant carries largely decides whether it is THC-dominant.

- Canonical: https://genetixbay.com/knowledge/glossary/thca-synthase.html
- Also written: THCAS, THCA synthase gene, tetrahydrocannabinolic acid synthase, THC synthase
- Glossary category: Cannabinoids and terpenes · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

THCA synthase (THCAS) is an oxidocyclase enzyme that closes a ring in [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) to form [THCA](https://genetixbay.com/knowledge/glossary/thca.md). 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](https://genetixbay.com/knowledge/glossary/gene.md) 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](https://genetixbay.com/knowledge/glossary/allele.md) and non-functional [CBDAS](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) makes mostly THCA; one with functional CBDAS and non-functional THCAS makes mostly [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md); one with one of each tends toward a mixed profile. Genotyping tests can read these alleles in seedlings, telling a breeder the likely [THC](https://genetixbay.com/knowledge/glossary/thc.md):[CBD](https://genetixbay.com/knowledge/glossary/cbd.md) 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.

## Related terms

[CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md)

## Read more

- [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md)
- [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md)

## Sources

1. Sirikantaramas S, Morimoto S, Shoyama Y, et al. 2004. The gene controlling marijuana psychoactivity: molecular cloning and heterologous expression of Δ1-tetrahydrocannabinolic acid synthase from Cannabis sativa L. Journal of Biological Chemistry 279(38):39767-39774.
2. Taura F, Sirikantaramas S, Shoyama Y, et al. 2007. Cannabidiolic-acid synthase, the chemotype-determining enzyme in the fiber-type Cannabis sativa. FEBS Letters 581(16):2929-2934.
3. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004.