Researchers Tracking Fungus

Nearly one-third of the global rice production is lost each year to a disease known as blast. That much rice could feed 60 million people, a UA researcher said.

Martin Egan, assistant professor of plant pathology in the Dale Bumpers College of Agricultural, Food and Life sciences, obtained his Ph.D. in molecular plant pathology from the University of Exeter, UK, a leading institution in rice blast research. Egan recently received a $110,332 grant from the UofA Chancellor’s Innovation Fund to study the cell functions of M. oryzae, the blast fungus.

“It’s a serious threat to global food security,” Egan said.

Arkansas rice growers are responsible for about half of the rice grown in the U.S., so the disease is especially costly here.

The airborne disease is spread by spores that land on rice leaves and stick tightly, Egan said. Within eight hours, the spore germinates and forms a dome-shaped infection cell called the appressorium. This structure generates an enormous amount of pressure that builds up to allow it to punch its way physically through the leaf, where it begins colonizing the tissue and dampening the plant’s immune system.

“You don’t really see disease symptoms for about three days after infection, so it’s kind of silently colonizing the tissue,” Egan said.

This intrusion is made possible partly by a ring-shaped structure called a septin ring. The blast spores produce filaments made of septin, a class of protein. The filaments then grow into a ring structure where the appressorium is attached to the plant.

The septin ring is essential to spreading the fungus. Researchers are working to discover ways to stop that spread.

Egan and his co-investigator, Yong Wang of the U of A physics department, will be looking for other proteins that might play a role in controlling or regulating the septin filaments that build the septin ring.

Wang employs a Nobel Prize-winning technique called “super-resolution fluorescence microscopy” to help understand how the proteins that build the septin ring structures organize.

The technique, invented between 2006-2008, won the 2014 Nobel Prize in chemistry.

“Conventional fluorescence microscopy has a special resolution of 200 nanometers,” Wang said. “It’s not good for the proteins inside the bacteria, because the bacteria itself is about 500 nanometers in diameter, and the proteins are, like, 5 nanometers.”

The super-resolution technique is about 10-20 times better than conventional fluorescence microscopy, Wang said, allowing them to see the individual proteins inside the cells, bacteria or fungus.

“We would like to look at the septin ring at different time points and see how this ring structure develops,” Wang said.

Alvaro Durand-Morat and Lawton Nalley, both professors of agricultural economics and agribusiness, have researched and published reports on the global economic impact of the blast disease.

Rice is an important food staple for more than half of the world, according to a 2016 report by the professors. Therefore, the world supply must double by 2050 to keep up with the food demand from population growth.

Some strains of the fungus are quickly growing resistant to fungicides, so the need to identify new ways of addressing the disease is urgent.

Additionally, there is now a population of blast fungus that has adapted to infect wheat crops in South America.

“It’s the same organism, it’s just made a host leap,” Egan said.

Egan said one way of potentially preventing rice blast is planting cultivars that are genetically resistant to the disease. However, he also said the pathogen will adapt and overcome that resistance within a matter of one to three years.

Results from the researchers’ 2016 study showed that, by eliminating blast from production in the Mid-South, U.S. rice producers would gain $69.34 million annually and increase the rice supply to feed an additional one million consumers globally.

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