Plants Activate 'Wartime' Protein Production to Fight Invasion

Plants are constantly attacked by bacteria, viruses and other pathogens. When a plant senses a microbial invasion, fundamental changes occur in the chemical soup of proteins inside its cells, the workhorses of life. In a new study published in Cell, Duke University researchers have uncovered a key ingredient in plant cells that reprograms their protein-making machinery to fight disease.

Crop production lost each year due to bacterial and fungal diseases amounts to 15%, or about $220 billion. Plants rely on their immune systems to fight back.

Unlike animals, plants do not have specialized immune cells to carry the bloodstream to the site of infection. Every cell in a plant must stand up and fight to protect itself, quickly entering combat mode. When they are attacked, the priority shifts from growth to defense, and cells start synthesizing new proteins and suppressing the production of others. Then within 2-3 hours, everything is back to normal.

The tens of thousands of proteins produced in cells do many jobs: catalyzing reactions, acting as chemical messengers, recognizing foreign substances, moving materials in and out. To build specific proteins, genetic instructions packaged in DNA within the nucleus are transcribed into mRNA messenger molecules. This mRNA strand then enters the cytoplasm, where ribosomes "read" the message and translate it into protein.

A 2017 study found that certain mRNA molecules are converted into proteins faster than others when plants are infected. What these mRNA molecules have in common is a region at the front of the RNA strand that has repeated letters in its genetic code, where adenine and guanine are repeated over and over again.

In the new study, the research team shows how this region works in concert with other structures within the cell to activate the production of "wartime" proteins.

The research shows that when plants detect pathogen attack, molecular markers that normally instruct ribosomes to land and read mRNA are removed, which prevents cells from making their typical "peacetime" proteins. Instead, the ribosome bypasses the usual translation start point, uses the repeating As and Gs regions within the RNA molecule for docking, and starts reading from there.

For plants, fighting infection is a balancing act, the researchers say. Allocating more resources to defense means less resources are available for photosynthesis and other life activities. Producing too much defense protein can cause collateral damage: Plants with an overactive immune system grow stunted.

By understanding how plants strike this balance, the researchers hope to find new ways to engineer disease-resistant crops without compromising yield, and conducted most of their experiments with Arabidopsis. But similar mRNA sequences have also been found in other organisms, including fruit flies, mice and humans, so they may play a broader role in controlling protein synthesis in plants and animals.

This defense mechanism of plants is really efficient and powerful. Although plants have seemingly weak defenses without specialized immune cells, every cell in their bodies can step up at critical moments, adjust their priorities, produce more combat proteins, and fight the enemy. After the danger is lifted, they can return to their normal "peaceful mode" and continue to focus on growth. Plants fight infection, as if they have easily grasped the balance of resource allocation between "defense" and "growth". This is what humans need to learn and learn from when designing plant and animal disease resistance programs.

Collected by Lifeasible, a biotechnology company in the agricultural field that offers plant breeding, plant genetic engineering, plant genetic transformation, protein expression in plant system and plant tissue culture services for customers worldwide.

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