Novel Expansion Microscopy Technique for Detailed Plant Biomolecule Mapping

The study of plant cells is undergoing a transformation thanks to new research led by Kevin Cox, 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 recent study published in The Plant Journal, Cox and his team introduced ExPOSE (Expansion Microscopy in Plant Protoplast Systems), a technique that adapts expansion microscopy (ExM) for plant research.

Overcoming Imaging Limitations

Traditional imaging techniques often come with trade-offs. On one end, low-end microscopes are user-friendly but lack resolution and depth. On the other, high-end microscopes offer exceptional detail but can be expensive and require extensive data processing.

"We have the low-end microscopes, which are user-friendly but do not provide much depth and resolution. And then the high-end microscopes, where you have really good resolution and data, but it is a lot to process, and they are more expensive."

Kevin Cox, Assistant Professor, Washington University in St. Louis

This is where expansion microscopy provides a valuable alternative. Instead of relying solely on lenses for magnification, ExM physically enlarges biological tissues by embedding them in a hydrogel—a water-absorbing polymer that expands while maintaining structural integrity. This process makes cellular structures more visible under a standard microscope without the need for high-cost imaging systems.

Adapting Expansion Microscopy for Plants

ExM has been widely applied in animal studies, but its use in plant research has been hindered by the rigid cellulose-based cell walls that prevent uniform expansion. Cox and his team tackled this challenge by using protoplasts—plant cells with their walls removed—allowing them to successfully adapt ExM for plant systems. The result is ExPOSE, a method that provides high-resolution insights into plant cellular structures.

With ExPOSE, researchers can now visualize cellular details with enhanced resolution, making it possible to study the precise localization of proteins, RNA, and other biomolecules. For Cox, whose research focuses on cellular communication and response, this is a significant breakthrough.

"It gives us a better understanding of where these genes and proteins are, how they are functioning, and how they might play a role in cellular response."

Kevin Cox, Assistant Professor, Washington University in St. Louis

Expanding the Toolkit for Plant Biology

ExPOSE is just one piece of a broader imaging toolkit. Cox and his team explored how combining ExPOSE with techniques like Hybridization Chain Reaction (HCR) and immunofluorescence could further enhance the study of proteins and RNA within plant cells.

While ExPOSE is currently used for individual cells, Cox envisions broader applications for expansion microscopy in plants.

"We are trying to understand spatial information at a cellular level and then also, collectively, at a large scale."

Kevin Cox, Assistant Professor, Washington University in St. Louis

Future research aims to apply ExPOSE to entire plant structures—leaves, roots, and organs—to better understand intercellular communication and organization.

A Model for Future Research

At the heart of Cox’s research is duckweed, a small, rapidly growing aquatic plant that serves as an ideal model 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."

Kevin Cox, Assistant Professor, Washington University in St. Louis

This approach is especially valuable for investigating how plant cells respond to stressors such as infections or environmental changes. The ultimate goal is to apply these insights to crops—helping to develop more resilient, high-yielding, and faster-growing plants, ultimately enhancing food security and sustainability.