New insight into plant immune defenses

Plants are under constant attack from disease-causing organisms and to protect themselves they have developed a simple immune system. One defence mechanism is to trigger threatened cells to die and so remove the food source from the invading pathogen. Professor Loake and his team have uncovered what is happening inside the cells to control this process and in doing so have put an enzyme called NADPH oxidase in the spotlight.

Professor Loake said "Plants generate a short, sharp shock that kills off the cells around where the pathogen is trying to invade and essentially starves it out. But we recognised that something must be going on to make sure that the plant doesn't go into complete meltdown."

When a plant is attacked by a bacterium or a fungus, for example, there are various ways in which they perceive this attack. One of the common responses is to trigger the production of a chemical called nitric oxide (NO) and a class of molecules known as 'reactive oxygen intermediates' (ROI's), which includes things like hydrogen peroxide and 'free radicals'. As well as being very toxic to the invading organism, NO and ROI's are key to encouraging cells to die if they are threatened. NADPH oxidase comes into the picture because it is critical for the production of ROI's.

The team has found that there is a feedback loop where as the levels of NO go up, NADPH oxidase is altered by the addition of an NO molecule to its structure so that it doesn't work so well. This causes the level of ROI's to drop and cell death tails off.

"This is really exciting!" said Professor Loake "We know that if a human being makes NADPH oxidase that doesn't work properly then they can suffer from an immune deficiency called chronic granulomatous disease or CGD. People with CGD have a particularly hard time fighting off bacterial and fungal infections and often suffer from pneumonia and abscesses.

"NADPH oxidase is really important in plant immunity as well, and we've been able to show how it is regulated in a normal immune response. We hope that plant breeders will be able to use this information to develop disease-resistant varieties. Our discovery might also open new opportunities to treat human immune disorders, such as CGD."

Professor Douglas Kell, Chief Executive, BBSRC said "If available nutrition cannot meet the rise in global population we will face a crisis. Anything that can be done to support the development of new disease-resistant crop varieties with excellent underpinning bioscience research is good news. We must find out as much as possible, through studies such as this one, about how plants deal with invading pathogens so that we can develop new strategies to reduce the impact of disease on yields."

The research is also funded by the Engineering and Physical Sciences Research Council (EPSRC), the Darwin Trust, the Ministry of Education Malaysia, and via a Torrance Scholarship.