Food, paper, textiles, and biofuels are all produced using cellulose, an essential part of plant cell walls, but it is still unclear how this process is controlled within plant cells. A group of scientists at University of Penn have now discovered a protein that modifies the cellular machinery that produces cellulose and, in turn, gives that machinery stability. The design of more stable, cellulose-enriched materials for biofuels and other uses may be influenced by this new knowledge.
The cellulose synthase complex, a group of proteins found within plant cells, is responsible for assembling the chain of cells. The timing and speed of this process, as well as the length of the cellulose chain, are all influenced by its regulation.
The most common biopolymer on Earth is cellulose, but despite its significance, little is understood about the mechanisms that control its synthesis. In this study, we discovered a protein called calcium-dependent protein kinase 32 ( CPK32 ), and we verified that it chemically modifies one of the proteins in the cellulose synthene complex, ultimately aiding in regulating the process of biosynthesis.
The research team’s leader and professor of biochemistry and molecular biology at University of Penn Eberly College of Science is Ying Gu.
In a paper that appeared on July 11 in the journal New Phytologist, the researchers presented their findings.
The cellulose synthase protein CESA3 is chemically modified by the CPK32 protein, which is known as phosphorylation. This chemical modification adds a chemical compound by its name. These reversible modifications support a number of crucial biological processes in the cell. More than 500 proteins, known as kinases, can phosphorylate more than 200, 000 locations on proteins in humans. More than 43, 000 locations in the plant Arabidopsis, also referred to as thale cress and widely used in plant science, can be phosphorylated by more than 1, 000 kinases.
It was extremely difficult to determine which of the numerous kinases could phosphorylate cellulose synthase, according to Gu. We searched for proteins that directly relate to CESA3 using a screening method. This identified the kinase CPK32, and we then conducted a number of experiments to confirm that it does in fact phosphorylate CESA3, to pinpoint the precise spot where this happens on CSA3 and to ascertain how the plant is affected.
The CESA3 protein was then modified by the researchers to change the location at which the phosphor group is added, preventing phosphatrylation. Adult plants of mutated plants had stunted growth, and cells from the mutant plants, where CESA3 phosphorylation was not possible, had reduced cellulose content and decreased stability of the chromatase complex.
Previous research has demonstrated that CPK32 is involved in a number of biological processes, such as the growth of pollen tubes and the development of shoots and roots, according to Gu. Here, we show how CPK32 performs a novel role in stabilizing the cellulose synthase complex and how phosphorylation works.
The next step for the researchers is to determine whether CPK32’s phosphorylation of CESA3 is distinct from that of any other kinases in the same family that can control cellulose biosynthesis in a similar manner.
Gu stated that by controlling the stability of the cellulose synthase complex, we might be able to persuade cells to make longer chains and, in the end, create materials that are rich in carbon.
Along with Gu, University of Penn’s research team also consists of Shundai Li, an assistant professor of biochemistry and molecular biology, Donghui Wei, a graduate student in plant biology at the time of the study, and Yiaoran Xin. Haiyan Zheng from Rutgers University and Ian Wallace from the University of Nevada, Reno, are also members of the research team.
The Center for Lignocellulose Structure and Formation, an Energy Frontier Research Center supported by the National Science Foundation, the University of Penn Department of Biochemistry and Molecular Biology, and the U.S. Energy Department, funded this study.