The way we study plant cells is expanding — literally — thanks to new research from , an assistant professor of biology in Arts & Sciences at Washington University in St. Louis and an assistant member of the Donald Danforth Plant Science Center. In a new study published in , Cox and his team describe how they have developed ExPOSE (Expansion Microscopy in Plant Protoplast Systems), a technique that brings expansion microscopy to plants.
Traditional imaging methods often come with trade-offs. “We have the low-end microscopes, which are user-friendly but don’t provide much depth and resolution,” Cox explained. “And then the high-end microscopes, where you have really good resolution and data, but it’s a lot to process, and they’re more expensive.”
That’s where expansion microscopy (ExM) comes in. Instead of relying on lenses to zoom in, ExM physically enlarges biological tissues by embedding them in a hydrogel, a water-absorbing polymer that can expand without losing its shape — the same type of material used in products like baby diapers. As the hydrogel swells, so do the cellular structures, making tiny details easier to see under a standard microscope. So, instead of a zoomed-in picture where individual elements may become blurred or distorted, the physical size of the cells increases, like a sponge in water. Better yet, it’s low cost and accessible.
While ExM has been widely used in animal research, applying it to plants has been challenging. Plant cells have rigid cell walls made of cellulose, which prevent uniform expansion.
Cox and his team tackled this issue by using protoplasts — plant cells with their walls removed — allowing them to successfully adapt ExM for plant research. The result is ExPOSE, a method that helps provide high-resolution, detailed views of plant cells.
With ExPOSE, researchers will now be able to visualize a plant’s cell structures with greater resolution, allowing them to study the precise location of proteins, RNA and other biomolecules. This is important for Cox, whose work is focused on cellular communication and response. “It gives us a better understanding of where these genes and proteins are, how they’re functioning and how they might play a role in cellular response,” he said.
A powerful new toolkit for plant biology
But ExPOSE is just one part of cellular imaging and data collection. Cox asked the question, “What other methods could we couple with this to make it more like a toolkit?” When ExPOSE was used in conjunction with techniques like hybridization chain reaction, commonly known as HCR, and immunofluorescence, Cox and his team found that they were able to see both proteins and RNA in even greater detail.
Although ExPOSE is currently used to study individual cells, Cox envisions an even bigger future for expansion microscopy in plants. “We’re trying to understand spatial information at a cellular level and then also, collectively, at a large scale,” Cox explained. That means using ExPOSE to look at organs, leaves, roots and, eventually, entire plants, where researchers will be able to investigate how these cells are communicating with one another.
At the center of Cox’s research is an unassuming but powerful model organism: duckweed. This small, fast-growing aquatic plant is potentially ideal for studying cellular communication and gene expression. “Because duckweed is so small, it gives us a model to understand what every cell is doing at a given moment,” Cox said. This is particularly useful when , such as infections or environmental changes.
The ultimate goal? Applying this knowledge to crops. By understanding how plant cells talk to each other and defend against threats, researchers could develop more resilient, higher-yielding and faster-growing crops, improving food security and sustainability.
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