How plants make cellulose for strength and growth?

Discovery reveals how plants create load-bearing structures that let them grow.

Cellulose is the primary substance found in plant cell walls and helps the plant to remain stiff and strong. Its building block glucose is a direct product of photosynthesis that captures carbon dioxide from the atmosphere.

Understanding, on a molecular level, how cellulose is produced could enable scientists to tailor its biosynthesis to alter the physical properties of cellulose, optimize carbon sequestration, or extract the stored energy to fuel human-made processes.

New research from the University of Virginia School of Medicine has shed light on how plants create this essential material.

The study reveals 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 made of molecules of glucose, a simple sugar, chained together; however, the new exploration outlines the molecular machinery plants use to do this. 

The scientists have created a blueprint of the factories plants use to make cellulose and to ship it to their cell surfaces. These factories are known as cellulose synthase complexes, and they sit inside the cell membrane to empower traffic across the cell boundary.

Scientists found that the factories produce three cellulose chains with parts located inside the cell. These factories also transfer 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.

The cellulose factories are far, far too small to be seen by a conventional light microscope.

Scientists mapped them out by tapping the power of UVA’s Titan Krios electron microscope. It allowed scientists to provide the first glimpse of the production and assembly of the world’s most abundant biopolymer.

Jochen Zimmer, DPhil, of UVA’s Department of Molecular Physiology and Biological Physics said“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. It is now more important than ever to invest in plant sciences.”

Journal Reference:
  1. Pallinti Purushotham et al. Architecture of a catalytically active homotrimeric plant cellulose synthase complex, Science (2020). DOI: 10.1126/science.abb2978

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