A female leafhopper (Macrosteles quadrilineatus). Image Credit: Zigmunds Orlovskis (CC BY 4.0)
The parasitic bacterium phytoplasma is a master manipulator. It turns its hosts into sterile ‘zombie’ plants that remain alive only to support the parasite. Phytoplasma secretes a protein called SAP54, which transforms the flowers of the plants into leaf-like structures. Until recently, scientists believed this transformation was how the parasite attracted tiny sap-feeding insects called leafhoppers, which act as vectors that transport phytoplasma to its next host. However, more recent research has shown that the transformation of flowers into leaf-like structures is not needed to lure leafhoppers to the plant. So, what is it about SAP54 that manipulates the preferences of leafhoppers?
To find out, Orlovskis et al. genetically modified plants to produce SAP54. They then carefully observed the number of male and female leafhoppers attracted to the mutant plants compared to plants that had not been genetically manipulated. They also used genetic analysis to investigate the proteins controlling the plant’s defence mechanisms.
Orlovskis et al. found that SAP54 attracted female leafhoppers to the leaves of the plant, but only when males were also present. SAP54 also suppressed the plant’s defences when males were on the leaves, making the plant more inviting to females. Increasing the number of females naturally facilitates breeding, resulting in more insects that can transport the parasite to new host plants.
A plant protein, called SHORT VEGETATIVE PHASE (or SVP for short), turned out to be critical in this process. Orlovskis et al. discovered that SAP54 promotes the breakdown of SVP, and plants lacking this protein also attracted more females when exposed to male leafhoppers. This suggests that SAP54 acts as a ‘molecular matchmaker’, helping male leafhoppers find mates by breaking down SVP in leaves. The involvement of SVP in attracting leafhoppers is surprising, as the family of proteins which SVP belongs to is primarily known for regulating developmental processes, such as flowering, rather than influencing how plants interact with their environment.
These findings deepen our understanding of the complex relationships between parasites, plants and insects, demonstrating how parasites manipulate both plant biology and insect behaviour. This knowledge could inform new strategies for controlling plant diseases spread by insects, potentially reducing crop losses caused by phytoplasma.
