But how it forms, and thus how it can be modified to design energy-rich crops, is not well understood. Now a study led by researchers at the Carnegie Institution's Department of Plant Biology has discovered that the underlying protein network that provides the scaffolding for cell-wall structure is also the traffic cop for delivering the critical growth-promoting molecules where needed.
The research, conducted in collaboration with colleagues at Wageningen University in the Netherlands and published in the advance online publication (AOP) of Nature Cell Biology on June 14th, is a significant step for understanding how the enzymes that make cellulose and determine plant cell shape arrive at the appropriate location in the cell to do their job.
"Cellulose is the most abundant reservoir of renewable hydrocarbons in the world," remarked Carnegie's David Ehrhardt, a coauthor. "To understand how cellulose might be modified and how plant development might be manipulated to improve crop plants as efficient sources of energy, we need to first understand the cellular processes that create cellulose and build cell walls."
Plant cells have rigid walls that cannot easily change shape. There are many cell types, spiky trichomes to fend off bugs and sausage-shaped guard cells that regulate the plant's breathing pores, as examples. In a previous study using the model plant Arabidopsis, Ehrhardt and team used groundbreaking imaging techniques to watch the molecules that create this array of shapes. It provided the first direct evidence for a functional connection between synthesis of the cell wall and an array of protein fibers—called microtubules—that provide the scaffolding that allow diverse plant cell shapes to be created as the cell wall pushes outward.
In that study, the group engineered plants to produce a fluorescent version of cellulose synthase, the enzyme that creates cellulose fibers. They also included a fluorescent version of tubulin, the protein from which microtubules are built. Using advanced imaging techniques, they tracked the motion of single fluorescent molecules, and found that cellulose synthase moves along "tracks" defined by the microtubules.
In this paper, the researchers looked at how the association between the cellulose synthase complexes and microtubules begins. The scientists were able to watch individual cellulose synthase complexes as they were delivered to the plasma membrane—the permeable film that surrounds the cell, but is inside the cell wall— and found that the microtubules not only guide where the complexes go as they build the cell wall, but microtubules also organize the trafficking and delivery of the cellulose synthase complexes to their place of action.
They also looked at the role in trafficking of a structural element called the actin cytoskeleton that helps move organelles and maintains the cell's shape. They found that it appears to be required for the general distribution of the cellulose synthase complexes, whereas microtubules appear to be required for final positioning.
When there is a disruption of the complexes through a stressor such as a rapid change in water movement (osmotic stress), active cellulose synthase complexes disappear and organelles accumulate just under the plasma membrane. These organelles contain cellulose synthase and are tethered to the microtubules by a novel mechanism. Previously Ehrhardt and team found that plant microtubules move by shortening at one end while lengthening at the other end. They do this one tubulin molecule at a time, in a process the researchers call treadmilling. They now think that the tethering discovered in this research allows the cellulose synthase-containing organelles to stay with the treadmilling microtubules for prolonged periods in times of stress. They found that when the stress abates, these organelles deliver the cellulose synthase to the membrane.
This work was supported by grants from the National Science Foundation (0524334) and the EU Commission (FP6 2004-NEST C1 028974).
The Carnegie Institution for Science (www.CIW.edu) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.
David Ehrhardt | EurekAlert!
Bioenergy cropland expansion could be as bad for biodiversity as climate change
11.12.2018 | Senckenberg Forschungsinstitut und Naturmuseen
How glial cells develop in the brain from neural precursor cells
11.12.2018 | Universitätsmedizin der Johannes Gutenberg-Universität Mainz
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
What if a sensor sensing a thing could be part of the thing itself? Rice University engineers believe they have a two-dimensional solution to do just that.
Rice engineers led by materials scientists Pulickel Ajayan and Jun Lou have developed a method to make atom-flat sensors that seamlessly integrate with devices...
Scientists at the University of Stuttgart and the Karlsruhe Institute of Technology (KIT) succeed in important further development on the way to quantum Computers.
Quantum computers one day should be able to solve certain computing problems much faster than a classical computer. One of the most promising approaches is...
New Project SNAPSTER: Novel luminescent materials by encapsulating phosphorescent metal clusters with organic liquid crystals
Nowadays energy conversion in lighting and optoelectronic devices requires the use of rare earth oxides.
Scientists have discovered the first synthetic material that becomes thicker - at the molecular level - as it is stretched.
Researchers led by Dr Devesh Mistry from the University of Leeds discovered a new non-porous material that has unique and inherent "auxetic" stretching...
10.12.2018 | Event News
06.12.2018 | Event News
03.12.2018 | Event News
11.12.2018 | Physics and Astronomy
11.12.2018 | Materials Sciences
11.12.2018 | Information Technology