One of the most spectacular phenomena in biology is the complete hijacking of hosts by pathogens such that hosts become ‘zombies’ destined to maximise pathogen survival.

Phytoplasmas induce dramatic changes in plant development, including proliferation of stems (witches’ brooms) and the reversion of flowers into leafy structures.

These bacterial pathogens produce small virulence proteins (effectors) that promote the degradation of TCP and reduced jasmonate (JA) synthesis and the conversion of flowers into leaves.

Phytoplasma effectors promote bacterial growth and insect vector colonisation. This is important, because phytoplasmas depend on sap-feeding insect vectors, such as leafhoppers, for transmission to a diverse range of plant species. Thus, bacterial effectors can reach beyond the host-pathogen interface to affect a third organism in a biological interaction.