Plants use a ‘trojan horse’ defense to fight mold infestations

Researchers at the University of California, Riverside, have made an exciting discovery in the ongoing war between plants and their fungal mold adversaries.

In a recent study, the team revealed a novel defense mechanism plants employ against the notorious gray mold, a fungus responsible for extensive damage to a wide array of crops worldwide.

Plants and gray mold

Gray mold, often recognizable as the fuzzy layer over spoiled fruits, is not just a nuisance in our refrigerators. It’s a formidable enemy in agriculture, attacking over 1,400 plant species and causing significant economic losses annually.

This mold’s aggressive nature has made it the second most destructive fungal threat to food crops globally.

The team, led by Professor Hailing Jin from UCR’s Microbiology & Plant Pathology Department, discovered that plants are not passive victims in this struggle.

Instead, they actively defend themselves by deploying tiny lipid vesicles, akin to inconspicuous bubbles, loaded with RNA molecules. These vesicles infiltrate the mold cells, unleashing their payload to sabotage the invader from within.

“Plants are not just sitting there doing nothing. They are trying to protect themselves from the mold, and now we have a better idea how they’re doing that,” said Jin.

Her team’s work builds on their previous findings, revealing that these extracellular vesicles carry small RNA molecules capable of silencing genes that empower the mold’s virulence.

The role of mRNA

The latest breakthrough shows that these vesicles also contain messenger RNA (mRNA) that disrupts critical functions within the mold’s cells.

“These mRNAs can encode some proteins that end up in the mitochondria of the mold cells. Those are the powerhouses of any cells because they generate energy,” Jin explained.

“Once inside, they mess up the structure and function of the fungal mitochondria, which inhibits the growth and virulence of the fungus.”

The reason why the mold accepts these lipid bubbles remains a subject of speculation. Jin suggests hunger might be the culprit, with the fungus unwittingly consuming these vesicles in search of nutrients, unaware of their hidden cargo.

This strategy is notably efficient for plants. “The beauty of delivering mRNA, instead of other forms of molecular weapons, is that one RNA can be translated into many copies of proteins. This amplifies the effect of the mRNA weapon,” Jin said. 

Plants’ stealthy defense against mold

Interestingly, this molecular exchange is not one-sided. Mold also uses similar vesicles to weaken plant defenses, a tactic evolved through a continuous co-evolutionary arms race.

These vesicles serve as an ideal transport mechanism for fragile RNA molecules, providing protection against degradation for both plants and fungi. Professor Jin highlights the broader implications of this discovery.

“During infections, there are always a lot of communications and molecule exchanges where plants and fungi try to fight against each other,” Jin said. “Previously people looked at proteins being exchanged. Now, modern technology has enabled us to discover another important group of players in this battle.”

Promise of RNA-based fungicides

Looking ahead, the research team is optimistic about leveraging this insight to develop eco-friendly fungicides. Jin envisions RNA-based fungicides that are safe, leaving no harmful residue and posing no threat to humans or animals.

“RNA-based fungicides would not leave toxic residue in the environment and would not affect humans or animals. RNA is present in most food, and it is easily digested,” Jin said.

“We are in a constant battle against pests and pathogens. Understanding and harnessing plants’ natural defenses, like mRNA delivery, could significantly enhance our ability to protect crops effectively.”

In summary, the battle against pests and pathogens is relentless, but armed with the knowledge gained from this study, researchers may potentially empower plants to more effectively combat the ongoing onslaught.

The full study was published in the journal Cell Host & Microbe.

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