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Septoria Pathogen “Hijacks” Wheat Crop Defences

26 January 2015

Wheat represents one of the most important food crops worldwide and its yields are continuously under threat from plant diseases often caused by pathogenic fungi.

Septoria tritici blotch (STB) is currently one of the most economically important of these diseases, and is caused by the fungal species Zymoseptoria tritici (also known as Septoria tritici or Mycosphaerella graminicola).

This disease causes premature death of wheat leaves, reducing the ability of plants to capture sunlight, which ultimately reduces their grain production. A new study from Rothamsted Research, strategically funded by BBSRC, and undertaken in collaboration with partners from Syngenta has revealed a novel strategy, which is used by Z. tritici to cause disease on wheat leaves. The work is published in the journal Plant Physiology.

The researchers aimed to identify the mechanisms by which the fungus manages to cause disease of wheat crops. To achieve this, the collaborators used a combination of advanced recent technologies, including RNA sequencing to measure gene activity along with quantification of natural biochemicals.

These methods and data collection allowed monitoring of changes in the physiology of the plant and the fungus simultaneously. Measurements were made throughout all phases of a disease interaction from the fungus landing on the leaf surface through to its reproduction (and potential spread) in infected leaves. These “large scale” datasets led to the discovery of new strategies used by the fungus to cause disease.

The study provides clear evidence for a cunning manipulation of the plants’ ability to defend themselves at different stages of infection. Whilst plant defences were supressed during early infection the actual appearance of STB disease symptoms on leaves involved a clear activation of plant defences.

This is counter intuitive to what one would expect and suggests that Z. tritici tricks wheat into a premature form of defence involving cellular suicide as it attempts to limit pathogen spread. However, the fungus reproduces itself well within this environment. This can be considered a form of eventual hijack of the wheat defence response.

Dr Jason Rudd, lead scientist at Rothamsted Research commented: “There was already evidence from previous work that Z. tritici did “something” to manipulate wheat’s defences. Our work now provides the clearest data so far that the pathogen must both initially suppress and then eventually activate plant defence during the course of successful infection.

"The many new Z. tritici genes, wheat genes and biochemicals identified in this study, provide an unparalleled resource for the development of tools that will support early identification of the disease and its subsequent management.”

Dr Kostya Kanyuka of Rothamsted Research says: “Z. tritici is very important pathogen of wheat with a unusual and interesting biology although the molecular mechanisms of the wheat-Z. tritici interaction remained largely unknown up until now. Our current study provides a wealth of molecular information and many candidate plant genes, fungal genes and pathways to test for their role in STB disease establishment in follow-on studies”.

Professor Kim Hammond-Kosack, leader of the wheat pathogenomics team at Rothamsted Research commented: “The combining of large scale transcriptome and metabolome analyses for both fungus and plant proved to be an exceptionally efficient way to explore the changing dynamics of the interaction throughout the long infection time-course.

"It is likely that in the future similar dual data sets will be generated for other fungal – wheat interactions. This approach should reveal whether other fungal species also ‘hijack’ the same or other plant defence responses to benefit their reproductive potential within the crop.

Further Reading

You can view the full report by clicking here.

January 2015

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