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A mustard plant infected with a particular parasite grows strangely, its development distorted by tiny invaders. Its leaves take strange shapes, its stems form a bushy structure called a witch’s broom, and it can grow flowers that do not produce seeds. Strangest of all, in a state of perpetual puberty, he lives longer than his uninfected siblings.
“It seems to stay in the youth phase,” said Saskia Hogenhout, a scientist at the John Innes Center in England. Aster Yellow phytoplasma.
The plant’s neighbors age, multiply, and die, but the dreaded young host of the phytoplasm survives. It becomes something of a mix between a vampire that never ages and a zombie host whose body serves the needs of its parasite, namely, encouraging the sap-sucking insects to feast on the plant’s bodily fluids for as long as possible. When the insects swallow the parasite, they spread it to new hosts, and the whole “Night of the Living Dead-Meet Dracula” cycle repeats.
How the parasite exerts such far-reaching control is more of a topic than casual curiosity among scientists – phytoplasmas can cause devastating diseases in crop plants such as carrots. Inside An article published in Cell magazine in SeptemberDr. Hogenhout and colleagues reveal that some of these startling changes are driven by the work of a single protein from the parasite, SAP05, that stands in the way of plant maturity.
SAP05 is not the first substance made by this phytoplasma that scientists have associated with the symptoms it causes. The team recently sequenced the parasite’s genome and identified a handful of proteins it could use to zombie their victims. But in the new paper, they explain how SAP05 drives some of the more surprising effects, such as lifespan extension.
It turned out that SAP05 binds to two groups of plant proteins that control the expression of genes used in development. Once locked into them, it causes them to be smashed by the facility’s own garbage disposal machines. As a result, the plants appear frozen over time, unable to move forward.
From the parasite’s point of view, this makes sense. If the host plants mature normally, they will grow flowers and produce seeds and devote all their energies to creating the next generation of plants. Before long, they would shed their leaves and dry up.
Dr. “You can imagine that this is not a perfect situation for the parasite,” Hogenhout said.
Parasites take advantage of the plant being sterile so they can focus their energy on making the microbe’s offspring. They also benefit from keeping the plant alive and full of delicious juices for as long as possible to make it easier for insects to feed on.
Interestingly, however, the scientists found that SAP05 binds to a very specific part of the cell destruction machine to accomplish this purpose. By changing the composition of this part, they can radically reduce the effects of SAP05. The plants—in this case Arabidopsis thaliana, the tiny mustard plant, a common laboratory model—did not grow into witches’ broom shapes with this modification and outlived uninfected plants.
But that didn’t mean they were any better. Plants designed to escape SAP05 had significantly shorter lifespans when infected by the parasite. SAP05 appears to provide some protection against the stress of an infection, making it easier for the host to carry. Without this, the plant may be more free to continue its maturation, but is more susceptible to disease than zombie plants, which are more resistant to other effects of the parasite. Zombies continue to live, protected by the organism living inside them.
Dr. This control is likely perfectly timed by the life cycle of sap-feeding insects, Hogenhout said. After insects feed on a plant and infect it with parasites, they lay eggs on it. Eggs mature at the same time the parasite takes over.
When the young beetles hatch after perhaps 10 days, the plants have enough time in their longevity to heartily feast on their juices before flying off. His good friends throughout the journey will be phytoplasma.
Dr. “The parasite has now multiplied just in time,” Hogenhout said.
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