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Two genes better than one for important plant pest

1 February 2011

Researchers funded by the BBSRC have revealed a novel molecular mechanism that triggers plant infection by Pseudomonas syringae, the bacteria responsible for bacterial speck in tomatoes. The scientists from the Department of Life Sciences at Imperial College London have revealed how two genes in the bacteria work together to launch the infection process that ultimately kills the plant's cells and causes disease, significantly reducing crop quality and yield.

Coloured electron microscopy image of a gold labelled (gold) pilus (blue), protruding from Pseudomonas syringae cell (left). © Professor John Mansfield

Coloured electron microscopy image of a gold labelled (gold) pilus (blue), protruding from Pseudomonas syringae cell (left).
© Professor John Mansfield

Pseudomonas syringae is responsible for major disease outbreaks in an enormous range of economically important food plants including rice, tomatoes, corn, cucumbers and beans. It is also a problem in wild plants and one Pseudomonas syringae type has recently infected half of all chestnut trees in the UK. The researchers hope that by understanding the molecular basis for how the bacteria attack plant cells they will be able to find new targets for pesticides and devise better strategies for disease management.

Speaking about the findings, published today (1 February 2011) in Nature Communications Dr Jörg Schumacher, the senior author on the study, explains: "These bacteria have quite a sophisticated system for infecting plants. They use remarkable needle-like structures called pili to penetrate and inject a range of proteins into a plant's cells, which then work to suppress its immune response and kill infected cells. Pseudomonas syringae are very versatile bacteria and their pili help them to infect a very large range of plants causing numerous symptoms in different plants, for example black/brown specks on tomato fruits."

Electron microscopy image of a gold labelled (black spots) pilus from Pseudomonas syringae cell. © Professor John Mansfield

Electron microscopy image of a gold labelled (black spots) pilus from Pseudomonas syringae cell.
© Professor John Mansfield

"From what we know, these bacteria only produce their pili and launch infection when they have already invaded the plant tissue. It is unclear how they sense the plant tissue environment that triggers infection, but we do know that the regulatory mechanism that controls pili formation is essential in this process."

What distinguishes Pseudomonas syringae from other related pathogens that also use pili to infect plants is that it has duplicated a gene during evolution that is involved in producing the pili. Indeed the researchers have found the duplicated gene in all the strains of Pseudomonas syringae they have studied, which makes them think that it is very likely to provide some selective advantage in the infection process. It appears, for example, that this innovation may allow for more subtlety when it comes to whether or not to commit to infection.

Dr Schumacher continues: "The motivation for this study was to find out how having a duplicated gene could provide Pseudomonas syringae with the 'edge' in terms of evolutionary advantage. We have studied related systems in other bacteria in great detail in the lab of Professor Martin Buck, where this study was carried out. What we have found here is that the two-gene system in Pseudomonas syringae is an evolutionary innovation that had not been described in bacteria.

"With our work and that of others we are able to understand how evolution that happens at the molecular level translates to phenomena we observe in our daily lives. When we see brown leaved chestnut trees next spring, chances are that Pseudomonas syringae and the duplicated gene are involved."

Professor Douglas Kell, BBSRC Chief Executive said: "With improvements in imaging and modelling we are now able to look deeper into cells at how the molecular machines that underlie all life on earth work. But this is not just knowledge for its own sake; a more detailed understanding of how crop pests interact with their hosts will be important for developing more sophisticated methods of controlling them. This is vital to global food security, ensuring that we can provide safe nutritious food to a growing world population."

This research was also supported by the Leverhulme Trust and the Wellcome Trust.

ENDS

Notes to editors

This research is published in February edition of Nature Communications: http://dx.doi.org/10.1038/ncomms1177.

Also see: Rappas M, Schumacher J, Beuron F, Niwa H, Bordes P, Wigneshweraraj S, Keetch CA, Robinson CV, Buck M, Zhang X. Structural insights into the activity of enhancer-binding proteins. Science (Mar 2005).

About Imperial College London

Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 14,000 students and 6,000 staff of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve global health, tackle climate change, develop sustainable sources of energy and address security challenges.

In 2007, Imperial College London and Imperial College Healthcare NHS Trust formed the UK's first Academic Health Science Centre. This unique partnership aims to improve the quality of life of patients and populations by taking new discoveries and translating them into new therapies as quickly as possible.

Visit ICL website at: www.imperial.ac.uk, the ICL twitter page at:  www.twitter.com/imperialspark.

About The Leverhulme Trust

The Leverhulme Trust was established in 1925 under the Will of the first Viscount Leverhulme. It is one of the largest all-subject providers of research funding in the UK, distributing funds of some £50M every year. For further information about the schemes that the Leverhulme Trust fund visit their website at www.leverhulme.ac.uk.

Electron microscopy image of a gold labelled (black spots) pilus from Pseudomonas syringae cell. © Professor John MansfieldColoured electron microscopy image of a gold labelled (gold) pilus (blue), protruding from Pseudomonas syringae cell (left). © Professor John Mansfield

About BBSRC

BBSRC is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £470M in a wide range of research that makes a significant contribution to the quality of life in the UK and beyond and supports a number of important industrial stakeholders, including the agriculture, food, chemical, healthcare and pharmaceutical sectors.

BBSRC provides institute strategic research grants to the following:

  • The Babraham Institute
  • Institute for Animal Health
  • Institute of Biological, Environmental and Rural Sciences (Aberystwyth University)
  • Institute of Food Research
  • John Innes Centre
  • The Genome Analysis Centre
  • The Roslin Institute (University of Edinburgh)
  • Rothamsted Research

The Institutes conduct long-term, mission-oriented research using specialist facilities. They have strong interactions with industry, Government departments and other end-users of their research.