Researchers have identified a previously unknown genetic region on the X chromosome in Cannabis sativa that appears to play a central role in how sex is determined in the plant. The findings, published in New Phytologist, point to three closely linked genes that together may influence whether a plant develops as male, female, or monoecious (bearing both male and female flowers).
This provides a more unified model for sex development in cannabis, an area that has long been scientifically complex and not fully resolved despite its importance for both cultivation and industrial production.
The Monoecy1 region on the X chromosome
The researchers identified a specific locus on the X chromosome, named Monoecy1, which appears to function as a key regulatory hub in sex development. Within this region, three genes were found clustered in a very small segment of DNA:
- CsREM16
- lncREM16
- CsKAN4
These genes show distinct expression patterns depending on whether the plant is monoecious or dioecious, suggesting that they operate as part of a shared regulatory network rather than acting independently.
Monoecy1 is also located in one of the most evolutionarily divergent regions of the cannabis sex chromosomes, indicating that it may have played an important role in sex determination throughout the species’ evolutionary history.
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A more complex system than a simple XY model
Cannabis sativa has traditionally been described as following an XY sex-determination system, where:
- XY = male plants
- XX = female or monoecious plants
However, the new findings suggest a more flexible and complex system. The same X-chromosomal region appears to influence both the development of separate sexes (dioecy) and the presence of both male and female flowers on a single plant (monoecy).
This indicates that sex determination is unlikely to be controlled by a single gene, but rather by an interacting network of regulatory elements.
A genetic network of three functional components
The three genes identified in Monoecy1 appear to form a coordinated regulatory system. CsREM16 is a protein-coding gene, lncREM16 is a long non-coding RNA gene, and CsKAN4 has a regulatory role.
Together, their combined activity may explain how cannabis switches between different sexual developmental pathways.
Reframing sex development in Cannabis sativa
Previous research has pointed to several candidate genes involved in sex determination, often linked to hormonal pathways such as ethylene signaling. However, the new study suggests these pathways must be understood within a broader framework where X-chromosome structure plays a central role.
The researchers used a combination of genetic mapping (QTL analysis), gene expression profiling, and comparative analysis of X and Y chromosome evolution. All approaches converged on the same region, strengthening the conclusion that Monoecy1 is a key control point.
An evolutionary pathway to monoecy
According to the researchers, monoecy may have emerged when genetic changes in X-linked regulatory regions disrupted normal female developmental programming. This could have resulted in XX plants developing both male and female flowers.
Such a trait may have provided an evolutionary advantage in certain environments and was later selected for in cultivation, where monoecious varieties can offer more uniform production.
Implications for future breeding
The discovery could have significant practical implications for cannabis breeding. A clearer understanding of the genes controlling sex development may allow for more precise control over plant traits, particularly in fiber production and flower yield.
At the same time, the findings contribute to a broader understanding of how sex chromosomes evolve in plants over time.
A new framework for plant sex biology
The study ultimately suggests that sex determination in Cannabis sativa should not be viewed as a simple XY system, but rather as a complex genetic network involving multiple X-linked genes working together.
This perspective may also be relevant for other dioecious plant species and could help reshape how researchers understand the evolution of sex chromosomes in the plant kingdom.
Source
Three closely linked X-chromosomal genes potentially control sex determination in Cannabis sativa
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