Pair of genes makes plant pest double trouble

Coloured microscope image of a pilus (blue) protruding from a Pseudomonas syring

Coloured microscope image of a pilus (blue) protruding from a Pseudomonas syringae cell (left). Image provided by Prof. John Mansfield.

Pair of genes makes plant pest double trouble

Research at Imperial could help scientists control one of the world’s most important crop diseases, Pseudomonas Syringae - News

Monday 7 February 2011
Adapted from a news release issued by the Biotechnology and Biological Science Research Council (BBSRC).

Researchers from Imperial College London have revealed this week how two genes in the bacteria Pseudomonas syringae work together to trigger an infection responsible for a range of deadly plant diseases.

Pseudomonas causes disease outbreaks in rice, tomatoes, corn, cucumbers and beans, as well as many wild plants, and has now infected half of all horse chestnut trees in the UK. The British Society for Plant Pathology has rated P. syringae as the most important plant pathogen worldwide.

The researchers hope that their gene discovery explaining how the bacteria attack plant cells so effectively will help them find new targets for pesticides and devise better strategies for disease management.

P. syringae have a sophisticated system for infecting plants: they possess tiny needle-like structures called pili which they use to inject a plant with a range of proteins which suppress its immune response and kill cells.

What distinguishes P. syringae from other pathogens is that it has duplicated a key gene involved in producing the pili. The Imperial researchers found this duplication in all strains of P. syringae they have investigated, suggesting that its presence is very likely to enhance the infection process.

"P. syringae are quite remarkable," said senior author on the study Dr Jörg Schumacher, from the Department of Life Sciences. " They can live on plant leaves for a long time before ’freezing’ rainwater to create sharp micro-icicles. These penetrate the leaf’s protective outer cells, damaging them and allowing the bacteria to enter. Once inside, they use their pili to infect more susceptible cells."

The researchers were investigating how a duplicated gene could provide P. syringae with the ’edge’ in terms of evolutionary advantage. They studied related systems in other bacteria in the lab of Professor Martin Buck , also in the Department of Life Sciences, and found that the two-gene system in P. syringae is an evolutionary innovation not previously described in bacteria.

Their findings demonstrate how evolution that happens at the molecular level translates to phenomena observed in daily life, say the researchers.

“When we see brown leaved chestnut trees next spring, chances are that P. syringae and its duplicated gene are involved," said Dr Schumacher.

Global trade of crops and live plants has helped P. syringae to spread and find new niches. Last year a number of new epidemics were reported, including outbreaks in peas in Turkey, broccoli and cabbage in South Carolina, kiwi in Italy and a particularly aggressive epidemic in tomatoes in Portugal. The bacteria infecting the British horse chestnut are thought to have come from India.

Professor Douglas Kell , BBSRC’s 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."

The research, published was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and supported the Leverhulme Trust and the Wellcome Trust.

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