Discovery reveals how plants make cellulose for strength and growth


Date:
July 9, 2020
Source:
University of Virginia Health System
Summary:
The discovery unveils the molecular machinery that plants use
to weave cellulose chains into cable-like structures called
'microfibrils.'


FULL STORY ==========================================================================
New research from the University of Virginia School of Medicine reveals
how plants create the load-bearing structures that let them grow --
much like how building crews frame a house.


========================================================================== Funded by the U.S. Department of Energy, the new discovery unveils
the molecular machinery that plants use to weave cellulose chains into cable-like structures called "microfibrils." These microfibrils provide
crucial support to the cell walls of land plants and allow them to build
up pressure inside their cells. This pressure lets plants grow towards
the sky.

"Cellulose is the most abundant naturally produced polymer, and its
building block, glucose, is a direct product of photosynthesis that
captures carbon dioxide from the atmosphere," said researcher Jochen
Zimmer, DPhil, of UVA's Department of Molecular Physiology and Biological Physics. "Understanding, on a molecular level, how cellulose is produced enables us to tailor its biosynthesis to alter the physical properties
of cellulose, optimize carbon sequestration or extract the stored energy
to fuel human-made processes." Constructing Cellulose Cellulose is
tough stuff and has accompanied and shaped human evolution from its
beginning. It is used to make building materials, clothes, paper, food additives and even medical tools. The polymer does not dissolve in water,
and microbes have a very hard time breaking it down. These are just a
few examples of cellulose's unique material properties.

Zimmer and his colleagues have shed light on how plants create this
essential material. Scientists have known that cellulose is made of
molecules of glucose, a simple sugar, chained together, but the new
research maps out the molecular machinery plants use to do this. In
essence, the scientists have created a blueprint of the factories plants
use to make cellulose and to transport it to their cell surfaces. These factories are known as cellulose synthase complexes, and they sit inside
the cell membrane to enable traffic across the cell boundary.

The factories, the researchers found, produce three cellulose chains with
parts located inside the cell. They also transport the polymers to the
cell surface through channels that traverse the cell boundary. These
channels release the cellulose chains toward a single exit point to
align them into thin fibrillar "protofibrils." Protofibrils emerge,
like toothpaste from a tube, as a strand.

They are then assembled with many others into microfibrils to perform
their essential functions in the cell wall.

Cellulose proto- and microfibrils are only a few nanometers thick --
a nanometer is a billionth of a meter. But their strength is in their
numbers.

Plants make microfibril after microfibril to support their cells. When assembled, the resulting structure is very strong. You might think of it
like how pieces of dry straw can be packed to make a durable, waterproof thatched roof.

The cellulose factories are far, far too small to be seen by a
conventional light microscope. To map them out, Zimmer and his colleagues tapped the power of UVA's Titan Krios electron microscope. This is a
machine so sensitive that it is buried deep underground, encased in
tons of concrete, to spare it even the slightest vibrations. It allows scientists to reveal a fascinating molecular world previously concealed
from human view.

In this case, it has allowed the research team to provide the first
glimpse of the production and assembly of the world's most abundant
biopolymer.

"We are already facing rapidly changing environmental conditions that
impact agriculture and food security around the world. In the future, understanding how plants operate on a molecular level will be increasingly important for population health," Zimmer said. "It is now more important
than ever to invest in plant sciences." The research was supported
as part of The Center for Lignocellulose Structure and Formation, an
Energy Frontier Research Center funded by the Department of Energy,
Basic Energy Science, award No. DESC0001090.


========================================================================== Story Source: Materials provided by
University_of_Virginia_Health_System. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Pallinti Purushotham, Ruoya Ho, Jochen Zimmer. Architecture of a
catalytically active homotrimeric plant cellulose synthase complex.

Science, 2020 DOI: 10.1126/science.abb2978 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200709141632.htm

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