Plants defend themselves against salmonella

Research scientists develop new approach to researching infections

Researchers from Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have transferred elements of salmonella known as effectors into tobacco plants. In doing so, they hope to explore how diseases and infections are spreading in both humans and animals. As strange as this may sound; there is good reason for doing so: plants have an immune system which is in some ways surprisingly similar to those of humans and animals. By examining how a plant’s immune system responds to the salmonella effectors, the researchers hope to be able to draw conclusions with regard to how they work. Their research findings have now been published in the renowned journal New Phytologist (http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2012.04124.x/abstract).

Salmonella and EHEC are two examples of bacteria which can trigger serious diseases in humans and animals. When this happens a very specific bacterial process occurs within the body. With a type of molecular syringe the bacteria inject harmful proteins – the effectors – which can then inhibit the body’s immune defence system. As a result, the infection in the body can spread unhindered. FAU researchers from the departments of biochemistry and medical microbiology have put these effectors under the microscope.

“Broadly speaking, we could say that in some ways we are not dissimilar to daisies – for example with regards to the transport of molecules within cells”, says Dr. Frederik Börnke from the department of biochemistry at FAU. Scientists believe that over the course of evolution some cell processes have been “conserved” and this is why they function in the same way in humans, animals and plants. A team of researchers headed up by Dr. Börnke are now exploring whether animal and plant cells also react in a similar way to an attack by pathogenic, i.e. disease causing, bacteria – and if so, to what extent. The initiative for the project can be traced back to student Suayib Üstün, who carried out research on the topic for his master’s thesis and has since received his doctorate from the department of biochemistry.

The research project

“Our research focuses in particular on Type III effector proteins from a strain of salmonella commonly found in animals”, explains Dr. Frederik Börnke. “Salmonella uses these proteins to multiply inside the cells it has attacked. And as a result the animals become sick.” As the salmonella strain cannot attack plants innately, the plant’s immune system should not actually react to the salmonella. Yet when the FAU researchers transferred the effector proteins into tobacco plants, surprisingly quite the opposite was observed: the SseF protein triggered an immune response in the tobacco plants characterised by hypersensitive cell death. The cells containing the salmonella effectors died off in a type of cellular suicide. Thus it seems plants can innately inhibit an infection from spreading any further in the tissue. By examining the immune response of plants, researchers have been able to draw the conclusion that the SseF protein attacks a cellular function which has been conserved over the course of evolution amongst animals and plants, and which could ultimately play an important role in the immune response to pathogens in both organisms in the future.

The scientists will be able to use the results of their study in various ways. On the one hand, it opens the door to future experiments on plants for research into the impact of pathogenic bacteria that attack humans and animals. On the other hand, it would prove a great advantage in terms of examining cell cultures and animal models, as plants can be cultivated more easily and more cost-effectively and are good to work with on a molecular biological level.

“Furthermore, our discovery provides us with at least the theoretical possibility of producing plants with immunity to these bacteria.” Epidemic outbreaks are becoming increasingly common due to increased consumption of raw fruit and vegetables which could be infected with salmonella or other forms of bacteria harmful to humans – EHEC is just the latest example of this. “Although salmonellae are not necessarily pathogens to plants, there is evidence to suggest that the bacteria are also capable of multiplying in plant tissue. If the plants were able to recognise the bacteria at an early stage, this could then potentially help contain the bacteria’s reproduction and in turn reduce the health risk to humans”, speculates Dr. Börnke.

The collaborative research area 796

The study was part of a sub-project carried out within the framework of the collaborative research area 796 (SFB) “Control mechanisms of microbial effectors in host cells”. The SFB is to receive €9 million in funding from the German Research Foundation and is located in the department for biochemistry at Friedrich-Alexander-Universität. The SFB’s spokesperson is Prof. Dr. Uwe Sonnewald. Within the framework of the research project the research scientists hope to investigate how diseases are caused by viruses and bacteria.

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