Stressed-out plants produce their own aspirin. Here’s how

They need to protect themselves from environmental hazards like insects, drought, and heat.
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Plant (right seedling) produces sunscreen to protect itself from damage caused by high light.Jin-Zheng Wang/UCR

Turns out plants are just like us.

We turn to medicines to relieve a headache or minor flu, and plants too have their ways of self-medication. They protect themselves from environmental hazards like insects, drought, and heat by producing salicylic acid, which is also known as aspirin used by humans for centuries to counter pain and inflammation.

Produced in chloroplasts, salicylic acid is usually generated in response to stress caused by climate change.

"It's like plants use a painkiller for aches and pains, just like we do," said plant biologist and study co-author Wilhelmina van de Ven from the University of California, Riverside (UCR), in a statement.

The researchers studied a model plant called Arabidopsis and published their findings in the journal Science Advances.

"We’d like to be able to use the gained knowledge to improve crop resistance," said Jin-Zheng Wang, UCR plant geneticist and co-first author of the new study. "That will be crucial for the food supply in our increasingly hot, bright world."

Biochemical analyses were performed on plants

Human skin produces ROS (Reactive oxygen species) in the lack of sunscreen. This causes freckles and burns. Similarly, environmental stresses result in the formation of ROS in plants which, at high levels, are lethal.

At low levels, however, ROS has an essential function in plant cells. "At non-lethal levels, ROS are like an emergency call to action, enabling the production of protective hormones such as salicylic acid," Wang said. "ROS is a double-edged sword."

So, to understand the complex chain of reactions that plants undergo when stressed, the researchers performed biochemical analyses on plants mutated to block the effects of key stress signaling pathways, and focused on an "initial alarm molecule" called MEcPP, which has also been seen in bacteria and malaria parasites.

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Plants in the Dehesh Lab at UC Riverside changing color in response to stress caused by high light conditions. Source: Jin-Zheng Wang/UCR

Salicylic acid helps plants withstand stresses

Going forward, the researchers want to learn more about MEcPP, also produced in bacteria and malaria parasites. Accumulation of MEcPP in plants triggers the production of salicylic acid, which in turn begins a chain of protective actions in the cells. 

The acid then protects the plants' chloroplasts, known to be the site of photosynthesis.

"Because salicylic acid helps plants withstand stresses becoming more prevalent with climate change, being able to increase plants’ ability to produce it represents a step forward in challenging the impacts of climate change on everyday life," said Katayoon Dehesh, senior paper author and UCR distinguished professor of molecular biochemistry.

"Those impacts go beyond our food," she continued.

Plants being in trouble are a harbinger of what the future beholds. That implies we're also in trouble.

"Plants clean our air by sequestering carbon dioxide, offer us shade, and provide habitat for numerous animals. The benefits of boosting their survival are exponential," she said. 

Abstract: Reconfiguration of the plastidial proteome in response to environmental cues is central to tailoring adaptive responses. To define the underlying mechanisms and consequences of these reconfigurations, we performed a suppressor screen, using a mutant (ceh1) accumulating high levels of a plastidial retrograde signaling metabolite, MEcPP. We isolated a revertant partially suppressing the dwarf stature and high salicylic acid of ceh1 and identified the mutation in a putative plastidial metalloprotease (VIR3). Biochemical analyses showed increased VIR3 levels in ceh1, accompanied by a reduced abundance of VIR3-target enzymes, ascorbate peroxidase, and glyceraldehyde 3-phosphate dehydrogenase B. These proteomic shifts elicited increased H2O2, salicylic acid, and MEcPP levels, as well as stromule formation. High light recapitulated VIR3-associated reconfiguration of plastidial metabolic and structural states. These results establish a link between a plastidial stress-inducible retrograde signaling metabolite and a putative metalloprotease and reveal how the reciprocity between the two components modulates plastidial metabolic and structural states, shaping adaptive responses.

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