An article describing the research appeared in the October issue of the journal The plant cell.

Cellulose, the structural component of plant cell walls, is an abundant and promising source of biofuels. However, common techniques for extracting cellulose from cell walls, which involve the removal of other large, tangled molecules called polymers, require chemical solvents, enzymes and high-temperature reactions, adding cost and complexity. complexity to the process. Improving understanding of how cell walls are constructed could shed light on new, more cost-effective ways to extract cellulose, researchers say.

“In recent years, researchers have explored various ways to potentially improve the efficiency of the cellulose extraction process, for example by manipulating other cell wall polymers that can get in the way, such as xylan and lignin.” , said Sarah Pfaff, a postdoctoral researcher in the Penn State Eberly College of Science who led the research. “But the unique structures formed by the cells of the ‘tracheary element of xylem’ often fail to develop properly in these mutant plants, causing the cells to collapse and ultimately reducing plant growth and the amount of extractable cellulose. In this study, we explore how these unique cell walls are assembled in healthy plant cells and also how this process goes wrong in mutants.

Xylem tracheary elements (XTEs) are a type of cell that allows water to pass from a plant’s roots to its leaves and have remarkably thick cell walls. Unlike other cells, Pfaff said, polymers like cellulose, xylan and lignin are deposited in specific locations in the cell walls of XTEs, creating a banding pattern. When these patterns don’t form properly in mutant cells, they can collapse under the pressure of water moving against gravity.

“The band patterns in the tracheary elements of the xylem act a lot like the wavy pattern of cardboard, adding stability to the cell wall,” Pfaff said. “Using traditional methods, it was difficult to observe individual cells to understand how this banding pattern breaks down in mutant cells. So we developed a method that allows us to observe individual cells without any of the neighboring cells don’t bother us.”

The new method leverages protoplasts, individual cells that have been stripped of their cell walls, to which researchers provide nutrients and what Pfaff calls a “genetic trigger” to differentiate into a new cell type. Although protoplasts have been used in various previous plant studies, the new method allows researchers to observe cells as they differentiate into a unique XTE cell type.

“We provide the protoplasts with a transcription factor – a kind of genetic trigger – so that they develop into a new cell type based on that signal,” Pfaff said. “It’s a bit like stem cells in that we can reprogram their developmental fate and watch them transform into entirely different cell types. In this study, we specifically induced the protoplasts of healthy and mutant plants to transform into tracheary elements of the xylem and observed how the band patterns were formed in their cell walls.

The researchers found that certain interactions between cellulose and xylan are necessary for the bands to form properly and that a properly assembled cell wall polymer network acts as a scaffold to dictate the banding pattern. They also found that in different mutant cells, the banding pattern failed in different ways.

“Previous research has focused on the impact of the inside of the cell on the cell wall, which is synthesized outside the cell, but we found that it also works the other way around,” he said. Pfaff said. “The structure of the cell wall can also impact what happens inside the cell, and they can interact with each other. This work provides important insights into how cell walls are created and how how these types of mutants might be viable in the future.”

According to Pfaff, understanding how cell walls are constructed is of interest to forestry, materials science as well as biofuel production. The research team plans to use their new method to explore how other types of cell walls are created.

“Instead of crossing mutant plants together to get several different genetic traits in a single plant, which can take several months, you can now explore different combinations in individual cells,” Pfaff said. “You could also use different types of genetic triggers to study other cell types, which could have implications in plant biology.”

In addition to Pfaff, the Penn State research team includes Edward Wagner, senior research technician, and Daniel Cosgrove, Eberly Family Professor of Biology. Penn State’s Center for Lignocellulose Structure and Formation, an energy frontier research center funded by the U.S. Department of Energy, and the Human Frontier Science Program supported this research.