Newly identified protein regulates the creation of cellulose in plant
cells

Date:
July 11, 2023
Source:
Penn State
Summary:
A team has identified a protein that modifies the cellular machinery
responsible for producing cellulose, which could inform the design
of more stable, cellulose-enriched materials for biofuels and
other functions.


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FULL STORY ========================================================================== Cellulose -- an integral component of plant cell walls -- is an important source of food, paper, textiles and biofuels, but how its creation is
regulated within plant cells has remained unclear. Now, a team led by researchers at Penn State has identified a protein that modifies the
cellular machinery responsible for producing cellulose, which ultimately
lends stability to that machinery.

This new understanding could inform the design of more stable, cellulose- enriched materials for biofuels and other functions.

Within a plant cell, a complex of proteins called the cellulose synthase complex builds a chain of cellulose. Regulation of this process determines
a variety of properties like when and how quickly it occurs as well as
the length of the cellulose chain.

"Cellulose is the most abundant biopolymer on Earth, yet despite
its importance, relatively little is known about how its synthesis is regulated," said Ying Gu, professor of biochemistry and molecular biology
in the Penn State Eberly College of Science and leader of the research
team. "In this study, we identified a protein called calcium-dependent
protein kinase 32 (CPK32) and confirmed that it chemically modifies one
of the proteins in the cellulose synthase complex, ultimately helping
to regulate the cellulose biosynthesis process." The researchers
published their findings in a paper appearing July 11 in the journal
New Phytologist.

The chemical modification carried out by the CPK32 protein is called phosphorylation; it adds a chemical compound known as a phosphor group
to the cellulose synthase protein CESA3. These types of modifications
are reversible and support a variety of important biological functions
in the cell. In humans, more than 200,000 locations on proteins can be phosphorylated by more than 500 proteins, which are called kinases. In
the plant Arabidopsis, also known as thale cress and commonly used in
plant science, more than 43,000 locations can be phosphorylated by more
than 1,000 kinases.

"Identifying which of the many kinases could phosphorylate cellulose
synthase was very daunting," said Gu. "We used a screening approach to
look for proteins that directly associate with CESA3. This revealed
the kinase CPK32, and we followed up with a series of experiments
to confirm that CPK32 actually phosphorylates CESA3, to identify the
specific location on CESA3 where this occurs, and to determine how this phosphorylation impacts the plant." The researchers then created a
version of the CESA3 protein with a mutation that altered the site where
the phosphor group is added, preventing phosphorylation. Cells of the
mutated plants -- where phosphorylation of CESA3 was not possible --
had reduced cellulose content and reduced stability of the cellulose
synthase complex, and adult plants of mutated plants had stunted growth.

"Previous studies have shown CPK32 plays a role in several biological processes, including pollen tube growth as well as shoot and root
development," said Gu. "Here, we demonstrate a new function of CPK32
and a novel mechanism of phosphorylation in stabilizing the cellulose
synthase complex." Next, the researchers plan to investigate whether
the phosphorylation of CESA3 is unique to CPK32 or if any other kinases
within the same family can similarly regulate cellulose biosynthesis.

"By regulating the stability of the cellulose synthase complex, we may be
able to encourage cells to produce longer cellulose chains and ultimately engineer cellulose-rich materials," said Gu.

In addition to Gu, the research team at Penn State includes Xiaoran Xin, graduate student in the Biochemistry, Microbiology and Molecular Biology program at the time of the research; Donghui Wei, graduate student in
plant biology; Lei Lei, graduate student in plant biology at the time
of the research; and Shundai Li, assistant professor of biochemistry
and molecular biology. The research team also includes Haiyan Zheng at
Rutgers University and Ian Wallace at the University of Nevada, Reno.

This research was supported by the Center for Lignocellulose Structure
and Formation, an Energy Frontier Research Center funded by the
U.S. Department of Energy; the Penn State Department of Biochemistry
and Molecular Biology; and the National Science Foundation.

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Source: Materials provided by Penn_State. Original written by Gail
McCormick. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Xiaoran Xin, Donghui Wei, Lei Lei, Haiyan Zheng, Ian S. Wallace,
Shundai
Li, Ying Gu. CALCIUM‐DEPENDENT PROTEIN KINASE32 regulates
cellulose biosynthesis through post‐translational modification
of cellulose synthase. New Phytologist, 2023; DOI: 10.1111/nph.19106 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/07/230711130631.htm

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