Friday, 31 July 2015

An international team of researchers, including scientists at The University of Western Australia, have discovered how parasitic plants, which steal their nutrients from other living plants, have evolved with the ability to detect and attack their hosts.

Their findings, published recently in the journal Science , could lead to new techniques to help farmers in developing countries fight weed infestation and boost food production.

Co-author of the study, Professor Charlie Bond from UWA’s School of Chemistry and Biochemistry said there are thousands of parasitic plant species, but the most burdensome for humans are those that infiltrate farmland and destroy crops.

Parasite infestations reduce crop yields by billions of dollars each year, particularly in developing nations where access to advanced herbicides and other control methods is limited.

In the new study, the researchers discovered how seeds of these parasitic weeds, which can lay dormant in the soil for decades, can detect when other plants are nearby, and begin to grow.

“In some ways this strand of research began over a decade ago with the discovery by Gavin Flematti and his colleagues at UWA that seeds can sense the presence of ‘karrikin’ molecules produced in smoke, and use this as signal to start growing after a bushfire” said Professor Bond.

Follow-up research at UWA by a team involving David Nelson, leader of the current study and now employed at the University of Georgia, and Dr Mark Waters, resulted in identification of the molecular receptor of the karrikin signal, a protein called KAI2.

Now, in a detailed study of the evolution of parasitic plants, they have found the gene for the ‘smoke detector’ protein has been duplicated, and some copies have switched to detecting a completely different family of signalling molecules, called strigolactones.

“As plant roots grow, they release strigolactones into the soil,” said Professor Bond. “This signal normally helps fungi form a beneficial connection to the plant, in which they each trade nutrients.”

However the study found the seeds of parasitic plants also possess the ability to sense strigolactones, which prompt them to germinate, attach to the host root and syphon off nutrients.

“It’s kind of like root radar,” said Assistant Professor Nelson. “But the incredible thing is that this strigolactone detection system seems to have evolved from plant genes that normally control a seed’s ability to detect fire.”

Team member and UWA PhD graduate Dr Rohan Bythell-Douglas said when the new variant proteins were identified the UWA team was the first point of contact due to their expertise in the structure of proteins, particularly KAI2.

“We were able to assist in the analysis of the genetic data and help build a three-dimensional picture of how a protein molecule can evolve from one signalling function to another,” Rohan said.

The findings may assist researchers in developing synthetic compounds that interfere with the receptors parasitic plants use to sense strigolactones, making them blind to the presence of a host.

“Or, it might be possible to create chemicals that mimic strigolactones,” Professor Bond said. “If these were sprayed over a field prior to the normal growing season, farmers could trick the parasitic plants by making them grow when there are no hosts present, a strategy known as suicidal germination.

“Ultimately, we hope this discovery can serve as the foundation for an easy and affordable treatment that farmers in developing countries can use to boost their food production.”

Other researchers involved in the study include Ken Shirasu from RIKEN in Japan and Jim Westwood from the Virginia Polytechnic Institute and State University in the USA.

Media references

Professor Charlie Bond (UWA School of Chemistry and Biochemistry)  (+61 8) 6488 4406 (+61 4) 23 052 177

David Stacey (UWA Media and Public Relations Manager)  (+61 8) 6488 3229 / (+61 4) 32 637 716


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