A new study published in New Phytologist identifies three closely linked genes on the X chromosome that may help control whether Cannabis sativa plants develop as male, female or monoecious.

Researchers from University College Dublin and Université Paris-Saclay used genetic mapping, transcriptomic analysis and X-Y chromosome comparisons to examine the biological basis of sex determination in Cannabis sativa, a species that typically produces male and female flowers on separate plants but can also produce monoecious plants with both flower types.

The study found that a region of the X chromosome, named Monoecy1, appears to be strongly associated with whether a plant is monoecious or dioecious. That region contains three genes within about 60,000 base pairs: CsREM16, lncREM16 and CsKAN4.

According to the researchers, the combined activity of those genes may help explain both male-female sex determination and the monoecious-dioecious distinction in Cannabis sativa. CsREM16 was linked to female expression, lncREM16 showed a male-associated pattern, and CsKAN4 was tied more closely to the difference between monoecious and dioecious plants.

The findings could have practical implications for hemp breeding. Monoecious hemp cultivars are often preferred for fiber production because they provide greater field uniformity, while dioecious cultivars include separate male and female plants that can mature differently.

Researchers also found that the Monoecy1 region is located in one of the oldest and most divergent areas of the Cannabis sativa sex chromosomes. The study notes that the terminal region of the X chromosome had the highest rate of genes lacking a Y-chromosome counterpart, supporting the idea that the area has played a key role in the evolution of cannabis sex chromosomes.

The authors conclude that the interaction of CsREM16, lncREM16 and CsKAN4 may provide a framework for understanding how sex is regulated in Cannabis sativa, while noting that additional genetic and environmental factors likely influence the trait.