Detection of cellular-level process behind crop-killing bacteria

A group of researchers from Nanyang Technological University, Singapore (NTU Singapore) has discovered a key process through which dangerous crop-killing bacteria can infect plants.

The Xanthomonas bacteria, commonly referred to as the ‘crop killer’, is a globally widespread bacterium that can infect as many as 400 different species of plant.

The scientists from NTU Singapore have now discovered the precise cellular-level process through which this crop-killing bacteria is able to break into a plant’s immune system and render them susceptible to dangerous infection.

The group’s results have been published in the journal Nature Communications.

Protecting crops from dangerous bacteria

The novel identification made by the team offers an advancement in understanding how to prevent bacterial infections in vital crops like rice, soybean, and tomato. Therefore, the findings of the study – led by Associate Professor Miao Yansong from the School of Biological Sciences, alongside Assistant Professor Yu Jing from NTU’s School of Materials Science and Engineering – will have significant consequences for food safety and sustainability.

“Xanthomonas is a plant pathogen that infects a variety of plants, including food crops, so understanding this mechanism is important for controlling crop diseases,” explained Miao. “This is relevant to Singapore’s and the world’s goals of growing more food.”

Understanding cellular-level mechanisms

The researchers analysed a specific kind of effector protein named XopR, which acts as a ‘molecular glue’. This study revealed that XopR takes control of the host cytoskeleton by undergoing a process known as liquid-liquid phase separation on the surface of the plant’s plasma membrane.

This phase separation process takes place in a similar manner to how oil and water can amalgamate but are also effortlessly divided into two distinctive liquids. During this process, both the XopR protein and the host plant cell interact with each other like liquid droplets, enabling the toxic effector proteins to ‘glue’ onto the plant cell and blend into it.

Once this has occurred, the inter-connected XopR proteins can penetrate and infect the plant cell’s actin cytoskeleton network and access cell behaviour. When this happens, the XopR protein can overwrite the existing cellular instructions to mount an immune response, therefore meaning the plant is left susceptible to infection.

Jing said: “Our study was not only a biological study of bacteria protein, but also about the biochemistry behind the infection mechanism. By studying the physico-chemical properties of XopR liquid droplets, we were able to further understand its unique protein sequence. This interdisciplinary approach allowed us to reveal the underlying molecular mechanisms by which XopR subverts the immunity of its plant host.”

This newly revealed process behind how effector proteins capture plant cells through phase-separation can be widely applied to other plant-pathogen interactions.  This is due to many other microbial pathogens also injecting effectors into the plant host, providing new avenues for future research.

Sustainability and food security

Xanthomonas can lead to bacterial spots and blights in both the leaves and fruits of the plants it infects. In some cases, if the disease takes root, a farmer’s only option is to cut down and burn the entire crop of plants to stem the spread of disease.

Thus, furthering knowledge of how crop-killing bacteria infects plants is a vital step in advancing techniques to avert their infection, as well as growing crops that can withstand the disease.

“Our research greatly advances our knowledge of previously unknown mechanisms by which bacterial effectors cause damage in a plant host cell. By understanding the exact mechanism of infection, our study sets the foundation for future research on how to prevent such infections through non-invasive means, such as changing plant growth conditions or using new nutrients. This allows us to better treat infected plants and explore ways to grow resilient crops with greater immunity to the disease without using genetic engineering,” added Miao.

The group of researchers from NTU Singapore has acquired a provisional patent for a toolkit they have established that enables scientists to replicate the process by which the XopR interacts with plant cells. This will allow researchers to experiment with possible solutions for bolstering crop immunity in laboratory settings. As well as this, it has exciting potential applications for future synthetic biology and agri-food technology.



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