Hitting back at 'wiretapping' parasite

Plant biologists at the University of California, Davis, have now shown that they can make plants resistant to dodder by attacking the junctions where the parasite taps into the host.

“We think that this will translate into other parasitic plants,” said Neelima Sinha, professor of plant biology at UC Davis, who led the project. The work was published online July 20 by the journal Plant Cell.

Sinha's lab uses dodder as a model for more serious parasites such as Striga, which attacks the roots of maize, sorghum and other African crops.

In earlier work, Sinha and colleagues found that when dodder taps into a host plant, it takes up RNA molecules that can act as chemical messengers in the host along with water, sugars and other nutrients. These circulating RNA molecules act as messengers inside plants, for example coordinating growth and flowering.

The researchers wondered if they could exploit this to attack the parasite. It is possible to switch off a gene with a short piece of RNA with which it pairs. This technique is called RNA interference or RNA silencing, and it won the Nobel Prize in medicine in 2006.

To use RNA interference against dodder, the team looked for genes that could affect the parasite but not the host.

“The answer turned out to be genes I've worked on all my career,” Sinha said, describing a group of genes that control the activity of other genes involved in shoot and root growth.

These genes are active in both the host plant meristem (an area of active growth in roots and shoots) and in the haustoria, the junctions where the parasite penetrates the host, Sinha said. So the researchers identified regions that were unique to the parasite, and used them to make a short DNA construct. Tobacco plants carrying this construct make short pieces of RNA that match the genes of the parasite, but not the host.

Dodder did not grow as well on the engineered plants as on control plants, Sinha said. At the same time, the dodder showed high levels of stress signals and flowered early — a reaction to stress.

The work was initiated by Steven Runo and spearheaded by Amos Alakonya, two African graduate students who have now returned to Kenyatta University in Kenya, Sinha said. They hope to develop the technique to control Striga in African maize crops.

“This is the proof of concept, and now we can take it into the field,” she said.

Other authors on the paper are: at UC Davis, postdoctoral researchers Ravi Kumar, Seisuke Kimura, Helena M. Garces, Julie Kang, Rakefet David-Schwartz; graduate students Daniel Koenig, Brad Townsley, and undergraduate student Andrea Yanez; and Jesse Machuka at Kenyatta University.

The work was funded by the Rockefeller Foundation and the National Science Foundation.
About UC Davis

For more than 100 years, UC Davis has engaged in teaching, research and public service that matter to California and transform the world. Located close to the state capital, UC Davis has more than 32,000 students, more than 2,500 faculty and more than 21,000 staff, an annual research budget that exceeds $684 million, a comprehensive health system and 13 specialized research centers. The university offers interdisciplinary graduate study and more than 100 undergraduate majors in four colleges — Agricultural and Environmental Sciences, Biological Sciences, Engineering, and Letters and Science. It also houses six professional schools — Education, Law, Management, Medicine, Veterinary Medicine and the Betty Irene Moore School of Nursing.
Media contact(s):
Neelima Sinha, Plant Biology, (530) 754-8441, nrsinha@ucdavis.edu
Andy Fell, UC Davis News Service, (530) 752-4533, ahfell@ucdavis.edu