While refrigerators keep food fresh and safe at safe temperatures, they can also be a breeding ground for fuzzy gray mold that spoils fruit. Most molds thrive in warm temperatures, but many can also grow in the refrigerator by producing spores. The spores can go airborne and accumulate inside the refrigerator and affect fruits and vegetables. However, plants may not be completely defenseless against this creeping fungus. According to a study published December 15 in the journal Cell Host & Microbe, plants use a stealth molecular weapon to counterattack the cells of gray mold.
[Related: A bit of care can keep your houseplants from sheltering harmful mold.]
What the team did was profile the messenger RNA (mRNA) molecules present in a plant called Arabidopsis thaliana–or Thale cress–against gray mold (Botrytis cinerea). mRNA are small molecules within the cells that have a set of instructions like a blueprint. While all three types of RNA can build proteins, mRNA is the one that acts like a messenger, delivering the recipe for a protein.
In the lab, they observed how the plants send small lipid “bubbles” called extracellular vesicles that are filled with RNA and the mRNA molecules that can attack the cells of the aggressive mold. Once the bubbles are inside, the molecules can suppress the infectious mold cells.
“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,” study co-author and University of California, Riverside microbiologist Hailing Jin said in a statement.
Jin’s team previously found that plants use these same bubbles to send small mRNA molecules that can silence the genes that make the mold more poisonous. This new study found that these bubbles have mRNA molecules that attack important cellular processes in the mold cells, including the functions of organelles.
“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,” said Jin. “Once inside, they mess up the structure and function of the fungal mitochondria, which inhibits the growth and virulence of the fungus.”
The team on this study is not entirely sure why the fungus accepts the lipid bubbles to begin with. They believe that the fungus may simply be hungry. Fungi may take in the bubbles for the nutrients, unaware that there is something dangerous inside. For the plants, this is an efficient strategy because one tiny mRNA molecule can have a large effect on the fungus. According to Jin, molecular weapons with mRNA can be translated into millions of copies or proteins and amplify their effect.
Interestingly, mold uses these same lipid bubbles to deliver small, damaging RNAs into the plants that they infect.
