Image: Photo Giddy, Flickr

Enter phytoplasma, a tiny parasitic bacterium that relies on plants to survive. Once inside a host, the parasite needs a way to get from plant to plant, so it's developed a very clever way of spreading: it turns the host plant into the living dead. 

Parasites have long been known to zombify their hosts ... it’s a great way to ensure survival – after all, if you're a parasite and your host has an agenda that competes with yours, you’ve got parasite problems.

For phytoplasmas, the problem is in the petals. The bacteria are able to move from plant to plant in the saliva of leafhoppers, sap-sucking insects that feed on grass, brush and trees. As leafhoppers come to feed on the host plant, they carry and pass along the infectious phytoplasmas to whichever plant they hop to next. 

To a leafhopper, a nectar-filled flower is of little interest, so a phytoplasma inside a flowering plant is less likely to make the move to a new host. Luckily, the bacteria swiftly work to do some demolition on their host’s floral blueprints. How do you get a flowering plant to stop flowering? Protein power. 

In a recent paper published in the journal PLOSBiology, researchers identified that phytoplasmas use a virulence protein called SAP54 (we’ll call it 'the instigator') to transform the host's flowers into green, leafy structures, which better attract hungry, or egg-laying, leafhoppers. 

zombie plant
Photo courtesy of PLOSBiology

'The instigator' exerts its flower-killing effects with help from another protein, RAD23 (we'll call it 'the muscle'), through a process called ubiquitination. Think of this like pytoplasmas hiring an assassin: 'the instigator' calls 'the muscle' to mark the targets, in this case, the plant's flowers. They are marked with ubiquitin, a tiny protein that signals a death sentence. The cell then moves these marked proteins to a structure called the proteosome to be recycled. By assassinating the marked traits, the phytoplasma has made itself an agenda-free host ... in essence a zombie plant that lives only to serve its master.

What's so amazing about this parasite is that none of its meddling affects the leafhoppers. This is because the process is so refined that the proteins are able to recognise a keratin-like substance in the plant that is absent in animals. Talk about some master manipulation!