Cellulose research could boost biofuel production

Proteins CSC1 and PTL1. Image courtesy of Charles Andrès; Inset Penn State.
Proteins CSC1 and PTL1. Image courtesy of Charles Andrès; Inset Penn State.

New insights into how plants build cellulose could have import implications for the production of biofuels, according to new research from Penn State University.

"Cellulose is the single most abundant biopolymer on earth," said Ying Gu, associate professor of biochemistry and molecular biology at Penn State and senior author of the paper published in the Proceedings of the National Academy of Sciences, in a statement from the university.

"It makes up about 95% of paper and 90% of cotton, and its derivatives are even in the emulsifiers in ice cream. In the past ten years or so, cellulose has also been considered as a major component of biofuels. Understanding how cellulose is synthesized may allow us to optimise its use as a renewable energy source."

Gu and colleagues’ study aimed to advance the understanding of how plants create cellulose.

“We knew that cellulose is synthesized in the plasma membrane that surrounds plant cells within a heteromeric protein complex -- a grouping of different kinds of proteins -- called the cellulose synthase complex, and that the main component of this complex is a unique cargo protein called cellulose synthase," said Gu.

"But we didn't know if other proteins are involved in the complex, or how the proteins get to the plasma membrane. To start answering these questions, we used a combination of approaches, including cell imaging, functional genetics, and proteomics, to create a timeline of events and to identify the main proteins involved in preparing the cell for synthesis."

Through their research, the scientists have gained insights into components that may contribute to the speed which the cellulose synthase complex travels to a cell’s outer membrane before synthesis.

Gu and colleagues show that a protein called cellulose synthase interactive 1 (CSI1) interacts with the cellulose synthase complex prior to synthesis. This may help mark the site at the plasma membrane where synthesis occurs.

They also demonstrated that CSI1 interacts with a separate complex called the exocyst complex. This complex is involved in transporting materials to the plasma membrane in a variety of species, as well as a protein called PATROL 1.

"We knew that the exocyst complex is evolutionarily conserved, with essentially unchanged structure in yeast and mammals, and here we confirmed its role in plants. But PATROL1 is a plant-specific protein that is not like anything we see in mammals or yeast. We are puzzled by what PATROL1 actually does and are excited to continue to investigate its function."

"We eventually hope to translate what we know about how plant cells build cellulose to more efficiently break it apart again for use in biofuels," said Gu, "ultimately increasing the efficiency of biomass-based energy production."

Gu’s colleagues in the research include Xiaoyu Zhu, Shundai Li and Xiaoran Xin at Penn State, and Songin Pan at the University of California, Riverside.

Proteins CSC1 and PTL1. Image courtesy of Charles Andrès; Inset Penn State.