The lethal weaponry of a fungus which has brought devastation to rice fields around the world has been discovered by scientists in a breakthrough that will help researchers to develop ways to tackle it.
Rice is the world's most important crop, with nearly half of the global population relying on successful harvests. The fungus destroys enough rice to feed 60 million people a year.
By understanding how the fungus attacks, scientists believe they will be able to formulate more effective fungicides and create genetically modified crops that can resist the pathogen.
"This is hugely important," said Martin Gilbert, a plant biologist at Exeter University in England. "Rice is especially important in the developing world and any handle we can get on better ways of tackling the fungus will help reduce the devastation it causes."
The rice blast fungus, Magnaporthe grisea, destroys the plants by puncturing holes in the leaves and slowly injecting proteins that break down the plant tissues. The fungus infiltrates and devours the plant.
The fungus is believed to be present in at least 85 countries and can infect domestic grasses; even burning rice crops to try to contain it is not always effective. In many parts of the world, it is resistant to fungicides and to genetic modifications created by plant breeders.
Researchers at Exeter University discovered a gene which is necessary for the fungus to secrete the plant-destroying enzymes.
Some rice plants are able to detect the fungus' attack in time and can launch a defense by either beefing up cell walls or killing off leaves. But the specific signals the rice plant uses to detect the attack have remained a mystery.
In tests, the researchers knocked out a gene in the fungus, known as MgAPT2, and found that this in effect disarmed it. The change also triggered no defense mechanism in rice plants.
"We know this gene is absolutely required for the fungus to cause disease," Gilbert said.
The study was published in the journal Nature yesterday. Further work will focus on the variety of molecules the fungus pumps into rice plants; researchers know that only some trigger the self-defense system, and if those can be identified they could be incorporated into fungicides.
Last year, an international team of scientists decoded the entire genome of the fungus, hoping this would reveal other weaknesses that could be exploited to kill it or make rice more resistant.