LEARNING FROM THE 'HEALTHY' TO PROTECT THE 'INFECTED'
A novel mechanism has been identified which likely contributes to resistance against Septoria leaf blotch in plant species normally non-infected with the disease, providing the clues necessary to develop control methods in wheat.
Septoria leaf blotch is a highly damaging disease of wheat and scientists are looking for ways to manage it more effectively. Most studies have looked directly at the interaction between wheat and Septoria but, in a novel approach, scientists at Rothamsted Research, who are strategically funded by the BBSRC, have instead looked at how plant species that do not get infected by Septoria achieve resistance. Most plants are resistant to the majority of microbes, a phenomenon known as non-host resistance, or NHR. Using non-host tobacco plants and advanced molecular techniques, the scientists characterised several genes linked to protection against infection in a study just published in the journal New Phytologist.
Fungi and their potential host plants are locked in a battle the outcome of which is strongly influenced by the expression and function of their genes as they recognise and respond to each other during attempted infection. Understanding this interplay unlocks the mysteries of host and non-host plant resistance and opens them up to manipulation. Zymoseptoria tritici, the causal agent of Septoria leaf blotch, only infects wheat and no other plant species. Unlike many fungi that directly invade plant cells, this fungus is strictly extracellular (i.e. non-plant cell penetrating or apoplastic) entering the plant through stomata and remaining in between the plant cells throughout its life.
Dr Jason Rudd, a senior scientist at Rothamsted Research and co-author of this paper commented that “Using a combination of fluorescence microscopy, quantitative PCR, transient gene-expression and gene-silencing techniques we were able to show that gene expression and function in both the fungus and the non-host plant during attempted infection were surprisingly similar to those we had previously observed during successful infection of wheat by Septoria.”
The scientists found that genes for many of the secreted proteins, called “effectors”, used by Septoria to manipulate defences of its host plant wheat, were also expressed when this fungus was inoculated onto the non-host plant tobacco. Moreover, when these fungal effectors were expressed in tobacco leaves, they were recognised by the plant stimulating defence reactions.
Gene-silencing methods allowed the researchers to demonstrate that two tobacco genes in particular, encoding NbBAK1 and NbSOBIR1 proteins known to associate with a range of cell surface immune receptors, were involved in induction of plant responses following recognition of effectors secreted by the pathogen. “This interesting finding suggests that non-host plants may possess specific cell surface immune receptors recognising Septoria effectors, and this opens up avenues for the development of new methods to protect susceptible wheat plants from Septoria” said Dr Kostya Kanyuka, a senior scientist at Rothamsted Research and co-author of this paper.
“It is exciting to find this receptor mediated widespread recognition of proteins from a wheat-infecting fungal pathogen in a taxonomically distant non-host plant species and suggests that recognition of multiple non-adapted pathogen proteins may contribute to non-host resistance”, Jason added.
Septoria tritici blotch disease is one of the most severe foliar pathogens of wheat accounting for 70 % of fungicide applications; with fungicide insensitivity on the increase, this makes effective control very difficult. Studies like this one that increase our understanding of how plants defend themselves against infection are incredibly important. This study is particularly informative because it is one of the first to consider non-host resistance to a plant disease with an extracellular necrotrophic lifestyle.
Commentary on this article by Friesen, New Phytologist, 213: 7–9.
About Rothamsted Research
Rothamsted Research is the longest-running agricultural research institute in the world. We work from gene to field with a proud history of ground-breaking discoveries, from crop treatment to crop protection, from statistical interpretation to soils management. Our founders, in 1843, were the pioneers of modern agriculture, and we are known for our imaginative science and our collaborative influence on fresh thinking and farming practices.
Through independent science and innovation, we make significant contributions to improving agri-food systems in the UK and internationally. In terms of the institute’s economic contribution, the cumulative impact of our work in the UK was calculated to exceed £3000 million a year in 20151. Our strength lies in our systems approach, which combines science and strategic research, interdisciplinary teams and partnerships.
Rothamsted is also home to three unique resources. These National Capabilities are open to researchers from all over the world: The Long-Term Experiments, Rothamsted Insect Survey and the North Wyke Farm Platform.
We are strategically funded by the Biotechnology and Biological Sciences Research Council (BBSRC), with additional support from other national and international funding streams, and from industry. We are also supported by the Lawes Agricultural Trust (LAT).
For more information, visit https://www.rothamsted.ac.uk/; Twitter @Rothamsted
1Rothamsted Research and the Value of Excellence: A synthesis of the available evidence, by Séan Rickard (Oct 2015)
The Biotechnology and Biological Sciences Research Council is part of UK Research and Innovation, a non-departmental public body funded by a grant-in-aid from the UK government.
BBSRC invests in world-class bioscience research and training on behalf of the UK public. Our aim is to further scientific knowledge, to promote economic growth, wealth and job creation and to improve quality of life in the UK and beyond.
Funded by government, BBSRC invested £469 million in world-class bioscience in 2016-17. We support research and training in universities and strategically funded institutes. BBSRC research and the people we fund are helping society to meet major challenges, including food security, green energy and healthier, longer lives. Our investments underpin important UK economic sectors, such as farming, food, industrial biotechnology and pharmaceuticals.
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The Lawes Agricultural Trust, established in 1889 by Sir John Bennet Lawes, supports Rothamsted Research’s national and international agricultural science through the provision of land, facilities and funding. LAT, a charitable trust, owns the estates at Harpenden and Broom's Barn, including many of the buildings used by Rothamsted Research. LAT provides an annual research grant to the Director, accommodation for nearly 200 people, and support for fellowships for young scientists from developing countries. LAT also makes capital grants to help modernise facilities at Rothamsted, or invests in new buildings.