Fresh Science

Plants can listen in on bacterial communication and can even mimic this communication, possibly in an attempt to stop any attacks, according to a breakthrough in scientific understanding announced today in Melbourne.

Plants wage a constant underground battle with bacteria living in the soil, according to Dr Ulrike Mathesius from the Australian National University.

“We found that plants have a sophisticated surveillance system that might allow them to predict bacterial attacks, and then release chemicals directed at stopping attacks by specific bacteria,” she said. “This information may be important for those seeking crop plants with better defenses against diseases.”

Researchers around the world have known for several years that bacteria use chemical signals to get together in big enough numbers to attack a plant or animal, causing disease.  Colleague, Professor Dietz Bauer from the Ohio State University has shown that crop plants can produce chemical signals that mimic the language of bacteria to confuse bacteria and thwart this coordination.

“What we wanted to know was whether plants were just sending their mimic signals all the time or whether they were directed towards certain bacteria,” Dr Mathesius said. “After all, many bacteria in the soil are beneficial to the plants, and stopping the actions of good bacteria would be a disadvantage.  And no one knew for certain whether plants could actually detect bacterial small talk and act accordingly”.

Dr Mathesius created pictures of the thousands of proteins that a plant produces in response to different levels of bacterial signals. This meant they could pin point even small changes in a test plant in response to bacterial communication.

“To our surprise, many different plant responses were activated by the bacterial signals,” Dr Mathesius said. “Not only that, but responses varied when the plant was exposed to high or low concentration of the signals, and they varied according to whether good or bad bacteria were communicating.

“This means that plants appear to be able to tell the differences between large and small populations of bacteria in the soil, and between good or bad kinds of bacteria.

“We think this detection system has evolved during the millions of years plants and bacteria have lived together in the soil”.

Dr Mathesius now hopes to work with colleagues to find out more about how this plant detection and response system helps the plant to cope with infections of plants by beneficial or harmful soil bacteria.

On Wednesday Ulrike will be presenting her work to the public at the Great Australian Science Show at the Melbourne Museum along with 15 other Fresh Scientists selected from over 100 nominations.

Ulrike Mathesius

ARC Postdoctoral Fellow Australian National University

Plants listen in on microbe Morse

Plant responses to microbial signals

How do plants know what goes on around their feet? Surrounded by armies of microbes, plant roots juggle between welcoming friends and fighting off foes. Bacteria themselves coordinate their attacks on plants with communication signals. New research shows that plants can detect and intercept the secret language of bacteria and therefore be much more prepared for attacks than we thought. These studies support the role of this virus in breast cancer in Australia. If it can be shown that this virus causes cancer, the possibility of a preventative vaccine for breast cancer would be of enormous consequence.

Project description

Plants are surrounded by dirt and microbes, don’t have an immune system and still survived the last 400 million years or so. While plants provide both food and shelter for bacteria, plants also profit from symbiotic bacteria that help roots with nutrient uptake. But often bacteria invade and destroy plants, leading to many of our crop diseases. Bacteria don’t usually go hunting alone but in packs, coordinating their attacks on plants and animals by communication with chemical signals, so that strikes are only attempted when bacteria have reached a critical population size big enough to overcome a host. If bacteria have evolved intricate communication channels that enable them to plot attacks against platns, why wouldn’t plants have evolved means to listen to the bacterial small talk and anticipate their attacks? We think they have!

We used a technique to monitor thousands of proteins inside plants to find out which, if any, change in response to the chemical signals that bacteria communicate with. A bit of a gamble? As usual in science, it probably was, but we had some clues. Dietz Bauer from Ohio State University had shown before that plants can produce molecules that confuse the bacterial communication system because they act similarly to the bacterial signals but convey the wrong message: that there are more bacteria than in reality, thus possibly triggering an attack that the plant might easily overcome. If plants produce these ‘confusion signals’, they might also know more about the bacteria they are aimed at.

In 2000, I started to look for how plants respond to bacterial signals with the help of an Honours student (Susan Mulders) in the laboratory of Barry Rolfe at the Australian National University. With the cooperation of Dietz Bauer and Max Teplitski from Ohio State University, experts in the purification of the bacterial signals, roots were exposed to signals from symbiotic and pathogenic bacteria that plants interact with. To our surprise, more than 100 plant proteins were affected by the bacterial signals, many involved in defence mechanisms of plants. The proteins also siffered in response to signals from symbionts and pathogens, indication that plants might be able to differentiate between them.

The plant surveillance system for bacterial communication signals might give plants a head-start in their constant fight with bacteria and might enable us to design new crop plants with the ability to manipulate the bacterial community colonising their roots.

Personal details

Qualifications: PhD (1999) ANU; Diplom Biology (1995) Darumstadt University of Technology, Germany (equivalent to Honours)