Iowa State researchers feature latest science on damaging nematodes

A tiny worm that causes billions of dollars in damage to crops like soybeans will be in the scientific spotlight this month thanks to an article written by two Iowa State University plant pathologists.

The latest knowledge on how cyst nematodes attack plants was the lead article in PLOS Pathogens Pearls, a journal of the nonprofit open access science, technology and medicine publisher.

Thomas Baum, a Charles F. Curtiss Distinguished Professor in Agriculture and Life Sciences, and Parijat Juvale, an assistant scientist in the plant pathology and microbiology department, were invited to write the review for the Feb. 1 edition online at http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1006791. The PLOS Pathogens Pearls series presents non-technical research pieces covering hot topics in the area of pathogen infection, as well as their human, agricultural and economic consequences.

“It will draw attention to the field of plant nematology because PLOS Pathogens is a journal with a wider audience that is not focused only on plant diseases, but diseases in general. That’s the beauty of this, it gets the message out to an audience than would otherwise see it,” said Baum, who also is chair of the plant pathology and microbiology department.

The information represents the collective advances of many scientists from around the country and the world, whose work in the U.S. has been funded by the U.S. Department of Agriculture, the National Science Foundation, and for a large part with soybean checkoff dollars.

“This is the state of the art of our understanding of the molecular mechanisms at work when the cyst nematode infects the plant, heavily emphasizing the molecular signals, so-called effector proteins, the worm sends to the plant,” said Baum, who has been studying the parasite for more than 20 years.

Baum and Juvale write about cyst nematodes, specifically the sugar beet and soybean cyst nematodes. The soybean cyst nematode is responsible for causing an estimated $1.2 billion in losses to soybean yields each year, making it the most serious threat to sustainable U.S. soybean production. Cyst nematode-resistant soybean cultivars are available, but they do not control all nematodes present in a given field and, therefore, select for virulent nematode populations that can overcome available resistance genes, leading to a slow but steady erosion of resistance.

Much of the paper deals with the functioning of effector proteins that the cyst nematodes use to feed on a soybean plant’s root cell without killing it.

“This is a worm that needs a living cell. It becomes sedentary and does not move from cell to cell. It takes one place and says this is where I’m going to live and eat, and I need to make sure my fridge is full all the time,” he said.

The nematode does that by manipulating the plant cell, secreting the effector proteins. Baum has spent years trying to find what they are and what they do.

“This was a great opportunity to give a snapshot without going into the details. This is made more for a wider audience for those who are not expert nematologists, who want to get an idea of where does the science stand,” he said.

Years of study have identified more than 80 confirmed effector proteins, but researchers suspect there will be hundreds more. Baum believes scientists will eventually solve the SCN problem, but it will take time and sustained research efforts.

“We can do things to make the plant a very poor host to the worm, but then it’s also not a good crop anymore,” he said. “This is an organism that is only alive because it has evolved mechanisms to parasitize a plant without killing it, and it’s been doing that for many millions of years. Over time, the mechanisms that didn’t work well didn’t make it, but those mechanisms that are at work today are very robust.”