Secret processes of cell wall formation revealed for the first time

Anyone who has ever looked at plants under a microscope will already have found the fascinating filigree patterns that can be formed by plant cells. Scientists from the Max Planck Institute for Molecular Plant Physiology and Wageningen University have now been able to study the formation of these cell structures and especially the cell walls in detail for the first time. To do this, they used highly specialized genetic engineering as well as optical analysis methods and complicated evaluation algorithms. This enabled them to delve deeper and deeper into the secrets of cell wall formation.

Sophisticated transport systems for water and nutrients

For plants to be able to transport nutrients upwards, they need a complicated network of different cells that perform specialized tasks. The tubular hollow structures, also called xylem, are of particular interest here. On the one hand, these fascinating cells are responsible for plant growth. They form particularly stable cell walls, the so-called secondary walls, which form an intricate and filigree pattern. The cells then die, become hollow, and are ultimately filled with lignin, the basic wood material, to solidify them. These miraculously created stable structures then become part of the perfectly engineered nutrient transport system.

However, the size of the xylem structures also largely determines how much water and nutrients plants can transport and thus how well they are adapted to climatic conditions. Until now, little research had been done on how these xylem vessels form and how they can adapt. All the more important, then, that Dr. Rene Schneider of the Max Planck Institute for Molecular Plant Physiology and Dr. Kris van't Klooster of Wageningen University took a closer look at this topic.

Microtubules create fascinating structures

The scientists paid particular attention to the formation of the stable and fascinatingly ordered cell wall structures. In their research, they penetrated ever deeper into the secret and seemingly perfectly coordinated processes of plant physiology.

One of their first findings was that cell walls are stabilized by the intercalation of cellulose. However, this intercalation does not seem to be random, but is supported and controlled by a large number of different proteins in the cell. But how do the proteins know where to accumulate?

This is where the so-called microtubules help, small tubular structures that, like assembly line workers, bring the proteins to the right places. The arrangement and distribution of the microtubules is thus also the template for the later cell wall structure. The next question was how and why the microtubules arrange themselves and organize themselves in such a way that the filigree patterns ultimately emerge.

Structures made visible with genetic engineering approaches

However, the team was hindered from delving even deeper into the formation of the mysterious structures by the complex structure of the plants. Since the xylem cells are covered by many different cell layers, it was very difficult to observe the processes inside. Here the scientists resorted to a trick: they used new approaches in genetic engineering to be able to solve this problem.

They used Arabidopsis (lat. Arabidopsis thaliana), actually an inconspicuous and widespread weed, as a model plant. The researchers modified the cells of the thale cress in such a way that not only the cells inside the plant, but all cells are capable of forming xylem and thus the secondary cell walls. To do this, the researchers developed the "gene switch" technology and were able to use it to get the cells to start producing the cell wall. Particularly outer cells, the so-called epidermal cells, were now particularly easy to observe under the microscope.

Fascinating processes under the microscope

For the detailed investigation of the process of cell wall formation, the scientists also developed an automated imaging technique. With its help, the process of cell wall formation could be recorded and digitally evaluated for the first time.

The researchers were able to observe that initially, microtubules were arranged in bands across the entire cell at the same time and formed initial structures. In further steps, the structures were refined and adapted. To this end, the microtubules in the bands grew steadily and were simultaneously degraded in the gaps. In the end, an even distribution of the ribbons was visible, which then remained for the rest of the cell's life.

The study team had to be patient in their research. While the formation of the evenly and parallel arranged bands took about two hours, the process to a fully functioning water-conducting cell was a matter of days. With the help of computer simulations, however, the researchers were also able to identify another protein called katanin. This protein appears to be responsible for the formation and degradation of microtubules and thus also for the rapid and orderly structure of the patterns.

With own research group further on the track of cell wall formation

However, research has not yet reached its end here. The control of the arrangement and the effect of the protein found, katanin, may be decisive in enabling plants to adapt to changing environmental conditions. Therefore, Dr. Rene Schneider would like to continue his research on the formation of secondary cell walls in the coming years.

He is supported in this by the German Research Foundation (DFG) and its renowned Emmy Noether Program. A grant of 1.3 million euros will allow him to establish a research group in Potsdam and to further investigate the genetic processes of cell wall formation in vivo (directly in the living plant) and in vitro (on parts removed from the plant). It may then be possible in the future to genetically modify plants so that they can grow and thrive even under unfavorable climatic conditions.

 

 

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