UNIVERSITY PARK, Pa. — A new method developed by Penn State biologists allows them to turn stripped-down plant cells into other types of cells, similar to the way stem cells differentiate into different cell types. Using this method, the research team explored the banding patterns that increase the stability of plant cell walls — much like the corrugated patterns in cardboard — and how they are created. Additionally, the researchers revealed how the assembly of these structures can go astray in different mutant plant cells, which they said could ultimately inform methods to break down plant cells for biofuels.
A paper describing the research appeared in the October issue of the journal The Plant Cell.
Cellulose, a structural component of plant cell walls, is an abundant and promising source of biofuels. However, common techniques to extract cellulose from cell walls, which involve removing other entangled large molecules called polymers, requires chemical solvents, enzymes and reactions at high temperatures, which add cost and complexity to the process. Improving the understanding of how cell walls are built could illuminate new, more cost-efficient ways to extract cellulose, according to the researchers.
“In recent years, researchers have explored a variety of ways to potentially improve the efficiency of the cellulose extraction process, for example by manipulating other polymers in the cell wall that can get in the way, like xylan and lignin,” said Sarah Pfaff, postdoctoral scholar in the Penn State Eberly College of Science who led the research. “But the unique structures formed by ‘xylem tracheary element’ cells often fail to develop properly in these mutant plants, which causes the cells to collapse and ultimately reduces 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 allow water to move from a plant’s roots to its leaves and have remarkably thick cell walls. Unlike in 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 are not formed properly in mutant cells, the cells can collapse from the pressure of moving water against gravity.
“The banding patterns in xylem tracheary elements act a lot like the corrugated pattern in cardboard, adding stability to the cell wall,” Pfaff said. “Using traditional methods, it was difficult to see individual cells to understand how this banding pattern breaks down in mutant cells. So we developed a method that lets us observe individual cells without any of the neighboring cells getting in the way.”
The new method takes advantage of protoplasts, individual cells that have been stripped of their cell walls, which the researchers provide with nutrients and what Pfaff calls a “genetic trigger” to differentiate into a new type of cell. Although protoplasts have been used in a variety of previous plant studies, the new method allows the researchers to observe the cells as they differentiate into the unique XTE cell type.
“We provide protoplasts with a transcription factor — a sort of genetic trigger — so that they develop into a new cell type based on that cue,” Pfaff said. “It’s a bit like stem cells in that we can reprogram their developmental fate and watch them turn into entirely different cell types. In this study, we specifically induced protoplasts from both healthy and mutant plants to turn into xylem tracheary elements and observed how the banding patterns in their cell walls formed.”