A recently found parasitic bacterial manipulation technique used to halt plant maturity may give alternative ideas to preserve disease-threatened food crops.
Parasites remodel the creatures on which they feed to suit their demands, sometimes in extreme ways. Some plants undergo such significant modifications when under the control of a parasite that they are referred to as “zombies.” They no longer reproduce and exist solely to provide a home and host for parasitic infections.
There has been little knowledge of how this occurs on a molecular and mechanistic level until now.
The Hogenhout group at the John Innes Centre and partners identified a manipulation molecule generated by Phytoplasma bacteria to hijack plant development in a study published in Cell. When this protein enters a plant, it causes essential growth regulators to be broken down, resulting in abnormal development.
Phytoplasma bacteria are a type of microorganism known for their ability to reprogramme the development of their host plants. This bacterial genus is frequently responsible for the ‘witches’ brooms’ found in trees, where an abnormally large number of branches grow close together.
These bushy outgrowths are caused by the plant remaining in a vegetative “zombie” state, unable to reproduce and therefore progressing to a ‘forever young’ status.
Aster Yellows, a crop disease caused by Phytoplasma bacteria, causes severe yield losses in both grain and leaf crops such as lettuce, carrots, and cereals.
Professor Saskia Hogenhout, corresponding author of the study said: “Phytoplasmas are a spectacular example of how the reach of genes can extend beyond the organisms to impact surrounding environments.
“Our findings cast new light on a molecular mechanism behind this extended phenotype in a way that could help solve a major problem for food production. We highlight a promising strategy for engineering plants to achieve a level of durable resistance of crops to phytoplasmas.”
The new findings demonstrate how the bacterial protein SAP05 manipulates plants by utilising part of the host’s own molecular machinery.
The proteasome is a piece of equipment that breaks down proteins that are no longer needed inside plant cells. SAP05 hijacks this mechanism, enabling plant proteins that regulate growth and development to be successfully discarded in a molecular recycling facility.
Without these proteins, the plant’s development is reprogrammed to favor the bacteria, resulting in the establishment of many vegetative shoots and tissues and a halt in plant aging
The scientists discovered the involvement of SAP05 in detail using genetic and biochemical experiments on the model plant Arabidopsis thaliana.
SAP05, interestingly, interacts to both plant developmental proteins and the proteasome. Direct binding is a relatively novel method of protein degradation. Normally, proteins destroyed by the proteasome are linked with a molecule called ubiquitin before degradation, but this is not the case here.
SAP05 targets plant developmental proteins that are related to proteins identified in vertebrates. The researchers wanted to see if SAP05 impacts the insects that spread the bacterium from plant to plant. They discovered that the structure of these host proteins in animals differs sufficiently that they do not interact with SAP05, and so the insects are unaffected.
This analysis, however, allowed the scientists to identify only two amino acids in the proteasome unit that are required to interact with SAP05. Their findings reveal that if plant proteins are modified to include the two amino acids found in insect proteins instead, SAP05 no longer degrades them, preventing the ‘witches’ broom’ aberrant growth.
This discovery opens the door to modifying only these two amino acids in crops, for example, using gene-editing technologies, to provide long-term resistance to phytoplasmas and the impacts of SAP05.
Image Credit: Getty