Perspectives Online

CALS researchers play key roles in sequencing genomes of nematode species

There are numerous plant-parasitic nematodes in the world, but only a few are responsible for billions in agricultural damage globally every year. Nematodes are small worms that burrow into plant roots and feed off living cells. Now, scientists from N.C. State University’s College of Agriculture and Life Sciences have led one study and contributed to another sequencing genomes of two nematode species -- research that will help examine models for parasitism and may help elucidate ways of getting rid of the harmful worms.

Sequencing the genomes is the first critical step toward comprehensively understanding how the organism works and may pave the way for research on ways to fight the pest.

In one study, lead authors Dr. Charles Opperman and Dr. David McK. Bird, CALS professors of plant pathology, and colleagues have completed the genome sequence and genetic map of the Meloidogyne hapla, a microscopic, soil-dwelling worm known more commonly as the northern root-knot nematode. In another, N.C. State and Iowa State University researchers have contributed to the release of the annotated genome of the Meloidogyne incognita – the southern root-knot nematode. Dr. Eric Davis, William Neal Reynolds Professor of plant pathology in the College, headed up N.C. State's contribution to the genome sequence project.

The Meloidogyne hapla research could help lead to a new generation of eco-friendly tools to manage the ubiquitous parasitic worm, which, along with other species of root-knot nematode, causes an estimated $50 billion in crop and plant damage yearly, said Opperman, co-director of the Center for the Biology of Nematode Parasitism and, with Bird, the corresponding author on a scientific paper describing the research.

Researchers from the University of California-Davis, the University of California-Berkeley and the Joint Genome Institute also contributed to the study.

“The combination of a complete genome sequence with the genetic map makes this a unique and powerful system for the in-depth study of nematode-host interaction,” Opperman said. Besides being extremely important for the development of new and effective management strategies, the researchers say that the information gleaned from the genome sequence and genetic map will help scientists learn more about what they call the “themes of parasitism.”

“All parasites have to do the same things to infect their hosts, whether the hosts are plants, animals or humans,” said Bird, co-director of the Center for the Biology of Nematode Parasitism. "Plants offer an advantage over those systems because they are easier to manipulate experimentally and enable us to perform detailed experiments not easily done in animals and not possible in humans.

"Having 99 percent of the genome sequenced allows you to know not only what's there but to compare it to other nematodes to see what's missing from this genome," Bird said. "Finding potential Achilles' heels, what the nematode is getting from the plant and how is it really interacting with the plant are all more possible now."

Likewise, Meloidogyne incognita has some remarkable biological adaptations that make it a fascinating organism to study.

“Root-knot nematodes have the amazing ability to transform selected plant root cells into multinucleate 'giant cells' for feeding, and our research collaboration in the United States has been active for years in discovery of the nematode parasitism genes that control this process," said Davis. “The full genome sequence now allows the researchers to identify the full cache of parasitism genes in the nematode and to design ways to disrupt the parasitic process and protect crop plants.”

“This is considered to be one of, if not the most important plant-parasitic nematode species across the world,” said Dr. Thomas Baum, professor and chair of plant pathology and head of Iowa State's contribution to the genome sequence project. “Many of the nematodes that are really bad pathogens are very specialized on which plant they attack,” Baum said. “This nematode has a huge host range. For us nematologists, it is very interesting to see and challenging to study.”

Because the pest is so widespread, many nematologists around the world were eager to help with the project, which was led by a French researcher group with help from researchers in Belgium, Holland, Great Britain, Switzerland and the United States.

Chemical treatments for killing nematodes, called nematicides, are dangerous to humans and other animals, so they've been outlawed restricted in use for decades. Technology for controlling nematodes has advanced little in the past three decades.

Davis and N.C. State postdoctoral research associate Dr. Noureddine Hamamouch used the current known parasitism genes to identify the full suite of predicted parasitism genes in the root-knot nematode genome. Baum's group, including postdoctoral researcher Tarek Hewezi and assistant scientist Tom Maier, worked on a specific part of the genome and performed manual annotations of genes.

The Meloidogyne hapla study was published online in Proceedings of the National Academy of Sciences. The Meloidogyne incognita research was reported in the journal Nature Biotechnology.

-- NCSU News Services