Tiny floating plants called duckweeds cover the surfaces of ponds and lakes around the world. Easy and quick to grow – they double their biomass in just about two days – duckweeds are emerging as a powerful tool for both fundamental plant research and biotechnology. However, an essential tool has been missing so far: Researchers lacked a reliable way to introduce genetic changes. Now, an international research team led by Arturo Marí-Ordóñez at the Gregor Mendel Institute for Molecular Plant Biology of the Austrian Academy of Sciences (GMI) presents a new, reproducible procedure for genetically transforming Spirodela, a type of duckweed, and makes both protocols and strain publicly accessible. Their work is published in the journal New Phytologist.

Attractive to ducks – and to plant biologists

Anyone who has walked past a still pond has likely seen duckweed at work. Within days, these tiny plants divide and multiply, forming a green carpet across the water’s surface. Their tendency to appear quickly and almost everywhere explains the “weed” in their name, while “duck” reflects how attractive they are to waterfowl. In the laboratory, their capacity for rapid growth makes duckweed especially attractive: they are easy to cultivate, require little space, and allow scientists to observe many generations over short periods of time.

In fundamental research, duckweed is to complex plants what yeast is to eukaryotes—a fast and simple model system. “Duckweeds have lost many complex developmental features found in other plants, so they act as a reduced, simpler plant system for us to work on,” Marí-Ordóñez says. “At the same time, they are monocot flowering plants – like maize, rice, onions or bananas – so duckweeds can be used to understand some aspects of important crop plants.” Duckweeds also have potential for biotechnology: Grown in outdoor, indoor or even in vertical farming setups, large amounts of plant material can be harvested continuously, making duckweed a candidate for plant ‘bioreactors’ that could be used to produce biological molecules on a large scale.

The challenge of genetic modification

What has hampered duckweed’s use in biotechnology and fundamental research is the lack of a reliable method to make targeted genetic changes. Without such a method, researchers have not been able to consistently introduce transgenes, generate mutations or add markers such as GFP to track proteins and follow genetically modified plants. Marí-Ordóñez and his team at the GMI spent several years developing and refining a protocol for doing so in Spirodela, one type of duckweed.

To introduce mutations or tags into plants such as Spirodela, researchers rely on genetic transformation, a multistep process that starts by culturing the plants with the right hormones until they form a callus—a mass of undifferentiated, rapidly dividing cells. Because callus cells are actively dividing, they provide a window of opportunity to introduce new genetic material, typically using bacteria to deliver DNA into the cells. Researchers coax these cells to regenerate into a complete plant which contains the newly added or altered gene.

“Our first challenge was to find a strain that efficiently forms a callus and then regenerates reliably,” Marí-Ordóñez explains. Collaborating with the group of Shuqing Xu at the Johannes Gutenberg University in Mainz, the teams identified one strain that performs particularly well. The researchers have now made this Spirodela strain available for all researchers by depositing it in public duckweed stock centres, from which other labs can request it.

Extending the toolkit

Throughout the study, Marí-Ordóñez and his team focused on testing and establishing methods that other researchers could use and therefore optimized all steps involved in genetic transformation to arrive at a new protocol. To test reproducibility, they collaborated with the group of Meret Huber, also at Johannes Gutenberg University in Mainz, which was also interested in achieving genetic transformation in duckweed. By following the protocol step by step, the group was able to independently achieve genetic transformation and identified areas or steps of the protocol that could be improved and refined, coming together to a more robust methodology. Demonstrating that the method works reliably outside the original lab was a critical step toward making it broadly usable. “We have designed the protocol so that others don’t have to go through the pain and years of trial-and-error we experienced,” Marí-Ordóñez says.

Building on this foundation, the researchers also established CRISPR-based genome editing in Spirodela, including sequencing the strain’s genome to enable targeted mutations, and establishing infrastructure to browse the genome and tools to design components for generating mutations and manipulating gene expression. “This should make duckweed an attractive and accessible research model to a wider circle of scientists,” Marí-Ordóñez adds. In basic research, Marí-Ordóñez now aims to understand why Spirodela can express foreign genes transiently for much longer than is typically observed in plants. In parallel, the team is collaborating with groups interested in using duckweed to produce molecules of pharmaceutical interest. “These methods create new opportunities,” Marí-Ordóñez says, “both for researchers studying fundamental plant biology and for those exploring biotechnological applications in duckweed.”