Foiling Rice-Spoiling Fungus

Rice blast spoils between 10 and 30 percent of annual rice yields worldwide — enough to feed as many as 60 million people. Recent outbreaks of the disease, which also strikes wheat and grass crops, have ranged from Brazil to Bangladesh.

Plant pathologists at Nebraska have revealed how the fungus behind blast disease can evade rice’s first immune response and silence the molecular sirens that mobilize reinforcements. The team’s identification of a key fungal gene and associated protein could inform genetic modification efforts to combat the disease.

When a rice plant detects signs of fungal intrusion, it responds by unleashing a burst of reactive oxygen species – molecules that become toxic in large doses, alerting the rest of the plant to the threat and cueing secondary defenses.

The Nebraska team found that a protein called NMO2 helps the fungus feed on nitrogen-based molecules and suppress the damage from reactive oxygen species. In doing so, the fungus avoids detection long enough to build up its forces in living rice cells before spreading to and destroying others.

Plant pathologist Richard Wilson, recent doctoral graduate Margarita Marroquín-Guzman and colleagues concluded that the NMO2 gene also helps deploy so-called effector proteins that intercept the distress calls sent out by plant cells.

Rice has evolved genes to recognize effector-related damage and coordinate a counterattack. The team discovered that if the initial burst of reactive oxygen species is not suppressed, it can disrupt the accumulation of effectors and stymie the infection even without support from the plant’s backup defenses. The finding could redirect existing efforts or stimulate new approaches to fighting blast disease in rice and other crops.

“That’s a novel observation because it moves the point at which you can prevent the infection higher up the chain, to the surface,” Wilson said. “That would conceivably enable you to develop more general approaches to breeding.”

The National Science Foundation and the U.S. Department of Agriculture’s National Institute of Food and Agriculture fund this research.

Reprinted from Research at Nebraska 2016-2017 Report