Plants know how to fight common cold

TEXAS A&M (US) — Plants could teach humans a thing or two about warding off illness.

Unlike us, plants can’t simply move away from pathogens—they grow where planted, often in environments teeming with microbes and other substances ready to attack.

New research published in the journal Science shows how a regulatory circuit is able to turn a plant’s immune sensor on and off as needed.

“Plants and animals live out their lives mostly in good health, though they may have been subjected to a lot of pathogenic microbes,” says Libo Shan, assistant professor of plant molecular biology at Texas A&M University.

“Scientists all around the world have been interested in how a healthy host can fend off invasions of pathogens and turn off the defense responses promptly once the intruder risk factors are decreasing.”

In the circuit BAK1—a protein involved with cell death control and growth hormone regulation—recruits two enzymes, PUB12 and PUB13, to the immune sensory complex  and fine-tunes immune responses.

Basically, the surface of plant cells has sensors that can foresee a microbial invasion.  One of the best understood plant receptors is FLS2, found in the common laboratory plant Arabidopsis.

FLS2 is able to sense the bacterial flagellin, which is a part of the flagellum, or tail-like projection on cells which help it to move. When FLS2 perceives flagellin, a group of evolutionary conserved immune responses is activated to fend off bacterial attack, Shan says.

But if the immune response stays activated, the plant stops growing and producing.

“To avoid detrimental effects of long-lasting immune activation, plant and animal hosts need a way to switch the activation off,” she notes. “How that can be has been a mystery to scientists.”

The flagellin perception recruits the two enzymes to the receptor FLS2 complex, that add a biochemical signature tag, ubiquitin, to the FLS2 receptors which inform cells to degrade the immune sensors. As a result, immune signaling is decreased.

Knowing how immune signaling works may help researchers devise ways to help plants and animals—including humans—regulate their immune systems.

“We needed to understand the mechanism so that we can regulate it better,” Shan says. “The host needs to know when the signal is triggered (to fight off a pathogen). Then the immune response needs to go quickly up and then back down when it is no longer needed.”

This ability could lead to cures, rather than medical relief, from an assortment of ailments including allergies and autoimmune diseases, Shan says.

“Plants have figured out how to survive in terms of disease and pest resistance. What we learn from them at the molecular level might help us understand animal pathogens better.”

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