September 16, 2014

Research reveals how fungus invades plants

MANHATTAN, Kan. – Like a stealthy enemy, blast disease invades rice crops around the world, killing plants and cutting production of one of the most important global food sources.
Now, a study by an international team of researchers has shed light on how the rice blast fungus, Magnaporthe oryzae, invades plant tissue. The finding is a step toward learning how to control the disease, which by some estimates destroys enough rice to feed 60 million people annually.
The study will also advance the study of wheat blast.
The team, led by Barbara Valent, Kansas State University professor of plant pathology, found the fungus has evolved two distinct secretion systems that facilitate its invasion into rice plants.
“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,” Valent said.
Rice blast has been recorded throughout human history and occurs in all countries where rice is grown, including the U.S. 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 in the U.S. 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.
“Rice blast disease is a threat to global food security and it’s closely related to wheat blast,” Valent said. “Because those two crops are the most important food staples worldwide, learning about these diseases is incredibly important.”
The disease occurs when pathogenic micro-organisms on the plants secrete proteins the suppress the plant’s immunity. The goal of the study was to learn if fungi need different secretory systems to aid their invasion into host plants.
Researchers learned 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, we 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. We noticed that normal treatments that block protein secretion didn’t stop those effectors that end up inside rice cells,” Valent said.
“Identifying how these processes function will help us understand how disease micro-organisms evolve and prove pivotal in controlling blast diseases,” she said.

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