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Dr. Stefanie Ranf is testing whether mature plants with a LORE gene mutation are more likely to be infected with pathogenic bacteria. Credit: A. Eckert / TUM
Like humans and animals, plants defend themselves against pathogens with the help of their immune system. But how do they activate their cellular defenses? Researchers at the Technical University of Munich (TUM) have discovered that plant cell receptors identify bacteria through simple molecular blocks.
"The immune system of plants is more sophisticated than we thought," says Stefanie Ranf of the Phytopathology Chair at the TU Munich. In collaboration with an international research team, the biochemist discovered substances that activate plant defense.
Until now, scientists thought that plant cells – similar to those of humans and animals – recognized bacteria through complex molecular compounds, for example from the bacterial cell wall. In particular, some molecules composed of a fat-like part and sugar molecules, lipopolysaccharides or LPS, were suspected of triggering an immune response.
In 2015, the Ranf team successfully identified the respective receptor protein: reduced elicitation specific to lipo-oligosaccharides, or LORE for short. All experiments have indicated that this LORE protein activates the plant cell's immune system when it detects LPS molecules from the cell wall of certain bacteria.
Backtracking leads to the right path
"The surprise came when we wanted to study this receptor protein more closely," recalls Ranf. "Our goal was to determine how LORE distinguishes the different LPS molecules and for that we needed high purity LPS."
<div data-thumb = "https://3c1703fe8d.site.internapcdn.net/newman/csz/news/tmb/2019/1-howplantsdef.jpg" data-src = "https: //3c1703fe8d.site.internapcdn. net / newman / gfx / news / hires / 2019/1-howplantsdef.jpg "data-sub-html ="Arabidopsis thaliana the leaves are infected by simple infiltration under pressure of a solution containing the bacteria. Credit: Astrid Eckert / TUM ">
The researchers found that only LPS samples containing certain short-chain fatty acid components triggered plant defenses. Surprisingly, they found in all these active LPS samples extremely adherent fatty acid molecules. After months of experimentation, the team was able to separate these free fatty acids from LPS.
"When we finally succeeded in producing highly purified LPS, it became clear that the plant cell did not respond to it at all! It was therefore clear that the immune response was not triggered by LPS, but by these short fatty acids "Ranf.
Targeting the constitutive elements of bacteria
3-hydroxy fatty acids are very simple chemical components compared to much larger LPS. They are indispensable for bacteria and are produced in large quantities for incorporation into various cellular components.
"The strategy of plant cells to identify bacteria through these basics is extremely sophisticated, so bacteria need these 3-hydroxy fatty acids and can not bypbad the immune response," Ranf summarizes.
Fitness program for plants
In the future, these results could help in the selection or genetic engineering of plants with an improved immune response. It is also conceivable that plants treated with 3-hydroxy fatty acids have increased resistance to pathogens.
The research is published in Science.
Scientists are discovering new clues about how the body stores fat
"Bacterial medium chain 3-hydroxy fatty acid metabolites trigger immunity in Arabidopsis plants" Science, science.sciencemag.org/cgi/doi… 1126 / science.aau1279
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The immune system of plants detects bacteria through small molecules of fatty acid (April 12, 2019)
recovered on April 12, 2019
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