How a bacterium overcomes a tomato plant's defences and causes disease,by sneakily disabling the plant's intruder detection systems, isrevealed in new research out today (4 December) in Current Biology.
The new study focuses on a pathogen which causes bacterial speck diseasein tomato plants. This bacterial invasion causes black lesions on leavesand fruit. Severe infection can cause extensive and costly damage totomato crops, and researchers believe that understanding more about howthis microbe works could lead to new ways of tackling it, and otherplant diseases, without the need for pesticides.
Scientists have found that the pathogen is very effective at attackingtomato plants because it deactivates and destroys receptors whichnormally alert the plant to the presence of a dangerous disease - in thesame way that an intruder would deactivate the burglar alarm beforegaining entry to a house.
Professor John Mansfield from Imperial College London's Department ofLife Sciences, one of the authors of the paper, says: "Once thereceptors have been taken out, the plant's defences are 'offline' andthe bacterium is able to spread rapidly, feeding on the plant withoutencountering any kind of resistance."
Together with colleagues at the Max Planck Institute in Cologne andZurich-Basel Plant Science Centre, Professor Mansfield used anexperimental model plant called Arabidopsis, which is also affected bythe disease, to examine what happens at the molecular level whenbacterial speck infects a plant. The team found that the pathogeninjects a protein into the host cell, which then deactivates anddestroys, from the inside, receptors on the cell's surface which aredesigned to alert the plant to the presence of invading microbes.
Deactivating the receptors stalls the plant's defence mechanism in itsinitial stages - ordinarily the cell surface receptors would kickstart achain reaction leading to the production of antimicrobial compounds tofight and kill off the bacterial invader.
Professor Mansfield says: "This area of research has a widersignificance beyond black speck disease in tomato, because the microbesthat cause plant diseases probably all employ similar attackingstrategies to suppress resistance in their hosts. The more we understandabout how the pathogens that cause disease overcome the innate immunityto infection in crop plants, the better our chances of developingapproaches to disease control that do not require the use of potentiallyharmful pesticides"
Source: Imperial College London