The Mustard Plant Of Dorian Gray

Parasite condemns its host to a perpetual adolescence

A mustard plant infected with a certain parasite grows strangely, its development warped by tiny invaders.

Its leaves take on odd shapes, its stem forms a bushy structure called a witches' broom and it may grow flowers that do not produce seed. Most peculiarly of all, it lives longer than its uninfected brethren, in a state of perpetual adolescence.

''It looks like it stays in a juvenile phase,'' said Saskia Hogenhout, a scientist in England who studies the life cycle of the parasite, which is called Aster Yellows Phytoplasma.

The plant's neighbors grow old, reproduce and die, but the phytoplasma's eerily youthful host persists.  It becomes like a mix between a vampire that never ages and a zombie host whose body serves the needs of its parasite by tempting sap-sucking insects to feast on the plant's bodily fluids for as long as possible.

When the insects ingest the parasite, it spreads to new hosts.

Such parasites are of interest to more than scientists : Phytoplasmas can cause destructive disease in crop plants like carrots.

In a new paper, Dr. Hogenhout and her colleagues show that some of the creepy alterations are driven by the work of a single parasite-produced protein called SAP05, which stands in the way of a plant's maturation.

SAP05 is not the only substance made by this phytoplasma that has been linked to the symptoms:

The team pinpointed a handful of proteins that it may use in zombifying its victims. But in the new paper, they explained how SAP05 seems to drive some of the more surprising effects, like the life-span extension.

[Veronique Greenwood]


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