SCIENTISTS DISCOVER HOW NEMATODES ATTACK

By Ed Adcock

Soybean cyst nematodes have been found in fields in every Iowa county. The plant-parasitic microscopic roundworms cause an estimated loss of $1 billion dollars annually to U.S. soybean producers.

The pests get their name from the shell-like cysts, each containing hundreds of eggs, that persist in the soil until a susceptible plant is within reach.

Iowa State plant pathologists have made a breakthrough in the understanding of how cyst nematodes attack plants at the genetic level, providing the possibility of giving soybeans a way to fend off the pest.

Rosetta Green, an agricultural biotechnology company, licensed the technology last summer with the goal of developing nematode-resistant plants. The company’s agreement with the Iowa State University Research Foundation is based on research deciphering how cyst nematodes infect plants.

The research is led by plant pathologists Thomas Baum, professor and chair of plant pathology and microbiology, and Tarek Hewezi, an associate scientist.

Cyst nematodes are damaging pathogens of plants worldwide. The pests feed on plant fluids by attaching to the host plant’s roots.

Scientists previously discovered that nematodes hijack plant development by injecting cells with chemical signals that cause hundreds of cells to fuse into a feeding site.

Baum and Hewezi sought to understand how the nematode changes the plant’s gene activities for the purpose of turning it into a food source. The researchers’ new approach was studying microRNAs, which are powerful regulators of gene activity.

“These worms learned to communicate with these plants’ cells in a very subtle way,” Baum says.

The researchers used the plant Arabidopsis as the model because it has a relatively small genome, and studied how sugar beet cyst nematodes attacked it. They discovered a relationship one microRNA had with two genes that are associated with growth regulation.

Hewezi and Baum used molecular biology techniques to generate experimental plants in which the microRNA levels are elevated in roots attacked by cyst nematodes and they found these plants were not as susceptible to the nematode. And when they adapted the target genes to be unaffected by the microRNA, they found these plants were less susceptible as well.

“Our results indicate that the microRNA, together with its target genes, has a real function in the interaction and it’s required to a certain degree for the pest to attach to plant roots,” Baum says.

The Iowa Soybean Association funded research that led to the discovery, and the National Science Foundation recently funded a three-year study for $607,875 to continue work with Arabidopsis micro-RNAs during cyst nematode parasitism.