Beer and cannabis could share ‘sex switch’, UCD-lead study find

Researchers identify genetic “switch” that determines the sex of cannabis plants, and find the same system may exist in hops.

The study, published in New Phytologist, pinpoints a specific section of the X chromosome that influences whether cannabis plants develop as male, female, or both.

“It was known for quite a while that female cannabis plants possess two X chromosomes and male plants carry an X and a Y chromosome, but there are thousands of genes on those chromosomes,” said Associate Professor Rainer Melzer, senior author of the study.

“Which of those genes determines whether a plant becomes male or female was unknown.”

Within a small stretch of DNA, researchers identified three closely linked genes that act together to control both male and female development.

Using genetic mapping, genome sequencing and gene expression analysis, the UCD team, in collaboration with international partners, identified this region, known as Monoecy1, as a major control point for sex expression.

The same key genes were also found in hops, located in a matching region of the X chromosome.

This suggests the genetic “switch” predates the divergence of the two plants around 28 million years ago.

“We were quite surprised when a lot of evidence pointed to a small region on the X chromosome as a key driver of sex determination, because in many other species, including humans, the Y chromosome determines sex,” said Matteo Toscani, a PhD student at UCD and first author of the study.

The findings have practical implications for agriculture, particularly for crops like hops and cannabis where female plants are economically preferred.

In brewing, only female hop plants produce the cones that give beer its aroma and flavour, while in cannabis, female plants are cultivated for cannabinoids such as CBD.

Being able to identify and control plant sex could reduce crop losses and allow growers to reliably produce all-female plants for cannabinoid or hop cone yields, or uniform monoecious crops for fibre production.

The study was funded by Taighde Éireann – Research Ireland and led by researchers at UCD in collaboration with Université Paris-Saclay.