How Plants Brace Themselves Against Infection

Scientists have discovered that plants create a special brace to ensure accurate detachment of flowers and leaves, covering the ‘wound’ left behind with cutin.

AsianScientist (May 15, 2018) – In a study published in Cell, a team of scientists in South Korea have uncovered how plants degrade their cell walls. These findings also shed light on how plants protect themselves from infection after losing their leaves.

For leaves, flowers and fruits to drop, specific proteins known as cell wall processing enzymes need to act precisely to degrade the cell wall between the cells and facilitate cell-to-cell detachment. The opening left behind after abscission must then be quickly re-sealed to prevent bacteria and harmful substances from entering the plant.

In the present study, researchers at the Daegu Gyeongbuk Institute of Science and Technology (DGIST) and the Institute for Basic Science used the classic plant model, Arabidopsis thaliana, to investigate how plants overcome the physical constraint of cell walls and accomplish organ abscission.

They found that the detachment spot, also known as the abscission zone, consisted of two neighboring cell types: residuum cells (RECs) remaining on the plant, and secession cells (SECs) in the flowers or leaves being shed.

The two cell types in the abscission zone display different cellular activities and architectures. In particular, SECs form two to three layers of lignin with a honeycomb structure. On the detachment area, lignin acts as a molecular brace that may hold individual SECs together when they are shed from the plant. In addition, it might limit cell wall processing enzymes to a confined area, allowing precise abscission.

“The separation must be precise and minimal as the process transiently increases vulnerability to environmental peril,” explained Dr. June M. Kwak of DGIST, lead author of the study.

“Because of the light and rigid property of the honeycomb architecture, it is perhaps unsurprising that we find plant cells have evolved such a structure to accomplish a potentially dangerous cellular process with great accuracy,” she added.

Immediately after SECs are shed, RECs accumulate a thin cell wall, which is vulnerable to infections and external harm. To protect the newly formed cell surface, RECs shield themselves with a protective coating made of cutin, which is responsible for surface protection against pathogens. This indicates that non-epidermal RECs change their identity, turning into epidermal cells, and is particularly interesting as the specification of epidermal cell identity was thought to be restricted to the embryonic stage.

The formation of this cutin layer is distinct from the mechanism of plant wound healing. The latter provides a protecting barrier made of cork rather than cutin. How the two processes are related is still mysterious.

The article can be found at: Lee et al. (2018) A Lignin Molecular Brace Controls Precision Processing of Cell Walls Critical for Surface Integrity in Arabidopsis.

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Source: Institute for Basic Science; Photo: Pexels.
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