Plants do not have bones that hold them up as people do. Instead, they have cell walls that are hard enough to keep plants from bending over. These thick walls are made of a sugar-based material called cellulose. Researchers now have some insight into how this material forms and the role of another chemical called hemicellulose in the gluing process. The key is how plant molecules get from point A to point B within a plant.

“How the cellulose gets transported and then assembled in the cell wall is a holy grail problem in plant biology,” said Loren Hough, program manager for the Biological Systems & Synthetic Biology program in DOE’s Office of Science, Office of Basic Energy Sciences. “This study reveals how the building blocks for cellulose come together into the final product in the cell wall of the plant.”

Cellulose is a long chain made up of smaller molecules called glucose. One of the big mysteries is why cellulose gets assembled into such a rigid form within the plant.

Cellulose is produced in a specialized assembly line inside plant cells called the cellulose synthase complex. In a new study published in the journal Nature, researchers in China, led by Jiayang Li of the Chinese Academy of Sciences, looked closely at the assembly line with cryo-electron microscopy. The instrument enables researchers to examine proteins, like the cellulose synthases, when they are frozen in action, revealing details about how proteins perform specific tasks.

The researchers created cellulose synthase enzyme complexes that they could study with this cryo-electron microscope technique. They were then able to reconstruct a detailed model showing the protein complexes involved in the synthesis of cellulose.

The researchers found that hemicellulose acts like a glue that guides cellulose production within the cell walls of plants. The study revealed how the glues come together to create a strong matrix of cellulose chains.

“The researchers were actually able to see the hemicelluloses interacting with a transmembrane cellulose synthase complex as it is actually synthesizing cellulose chains,” Hough said.

Understanding this plant growth mechanism could lead to the development of new plants that produce more and stronger cellulose fibers. This improved material could be used to make biofuels, paper, textiles and other products.

“Cellulose is one of the most important renewable resources on the planet,” said Michael Himmel, director of the BioEnergy Science Center (BESC), a DOE Bioenergy Research Center (BRC). “This study is a breakthrough in our understanding of cellulose production in plants. It is exciting to think about the possibilities for the utilization of this vital resource in biofuels and other energy-related applications.”

The study also contributes to the DOE-funded Agile BioFoundry project. The Agile BioFoundry is advancing the frontiers of synthetic biology by developing an “agile foundry” that is capable of designing, making and testing new genetic circuits and whole cells from scratch. The work published in Nature is a prime example of agile foundries in action.

“This research showcases how fundamental discoveries related to plant biology can be accelerated by the Agile BioFoundry’s open-access synthetic biology platform,” said Chris Voigt, Agile BioFoundry director and professor of biomedical engineering at the Massachusetts Institute of Technology.