Researchers from the University of Exeter have improved understanding of a serious crop disease, which can kill plants and slash production of one of the most important global food crops.

Working as part of an international team, the Exeter scientists have exposed the way in which rice blast fungus invades plant tissue. They said the finding is a step towards learning how to control the disease, which by some estimates destroys enough rice to feed 60 million people annually.

After two years of research, the team, which includes researchers from institutions in the United States and Japan, discovered that the fungus invades plants in two different ways.

Professor Nick Talbot from the University of Exeter commented, "This discovery shows that there are two ways in which a disease-causing fungus can secrete proteins into plants. This is a big step forward for plant pathology and might eventually offer new strategies to control crop diseases important in food security."

Barbara Valent, Professor of Plant Pathology at Kansas State University and one of the contributing scientists, said,  "Knowing that a special secretion system is required for disease is significant, because it means we can block this system without harming other fungi that are critical for healthy ecosystems.

Researchers know that to cause plant diseases, pathogenic micro-organisms secrete proteins, called effector proteins, into the host plant's tissue, the proteins suppress the plant's immunity and support the pathogen's growth. The goal of the study was to learn if fungi need different secretory systems to aid their invasion into host plants."

Rice blast has been known throughout recorded history and occurs in all countries where rice is grown. In 1985, wheat blast emerged as a new disease sharply reducing wheat yields in Brazil. So far, wheat blast has only spread within South America and has not been detected any further north. Professor Valent is now leading a team of scientists focused on developing resources for rapid identification and elimination of the disease if it should arrive in U.S. wheat regions.

The researchers found that the rice blast fungus Magnaporthe oryzae has evolved a novel secretion system for effectors that go inside the plant cell. In contrast, effectors that end up in the space outside the plant cells are secreted by a classical system, which is shared by organisms from fungi to humans.

In this study, the international team focused on investigating how the fungus secretes effectors during invasion of rice tissue by producing strains secreting effectors linked to fluorescent proteins from jellyfish and corals. They performed microscopy to watch the fungus secreting these fluorescent proteins as it grows inside rice cells, and noticed that normal treatments that block protein secretion didn't stop those effectors that end up inside rice cells. Greater understanding of how these processes function will be crucial in efforts to tackle blast diseases.