Parasitic weeds are ruthless freeloaders, stealing nutrients from crops and devastating harvests. But what if farmers could trick these invaders into self-destructing? Scientists at UC Riverside think they've found a way.
Across sub-Saharan Africa and parts of Asia, places already struggling with food insecurity, entire fields of staples like rice and sorghum can be lost to a group of insidious weeds that drain crops of their nutrients before they can grow. Farmers battle these parasites with few effective tools, but UCR researchers may be able to turn the weeds' own biology against them.
This trick is detailed in the journal Science, and at its heart lies a class of hormones called strigolactones — unassuming chemicals that play dual roles. Internally, they help control growth and the plants' response to stresses like insufficient water. Externally, they do something that is unusual for plant hormones.
"Most of the time, plant hormones do not radiate externally — they aren't exuded. But these do," said UCR plant biologist and paper co-author David Nelson. "Plants use strigolactones to attract fungi in the soil that have a beneficial relationship with plant roots."
Unfortunately for farmers, parasitic weeds have learned to hijack the strigolactone signals, using them as an invitation to invade.
Once the weeds sense the presence of strigolactones, they germinate and latch on to a crop's roots, draining them of essential nutrients.
"These weeds are waiting for a signal to wake up. We can give them that signal at the wrong time — when there's no food for them — so they sprout and die," Nelson said. "It's like flipping their own switch against them, essentially encouraging them to commit suicide."
To understand strigolactone production, the research team led by Yanran Li, formerly at UCR and now at UC San Diego, developed an innovative system using bacteria and yeast. By engineering E. coli and yeast cells to function like tiny chemical factories, they recreated the biological steps necessary to produce these hormones. This breakthrough allows researchers to study strigolactone synthesis in a controlled environment and potentially produce large amounts of these valuable chemicals.
The researchers also studied the enzymes responsible for producing strigolactones, identifying a metabolic branch point that may have been crucial in the evolution of these hormones from internal regulators to external signals.
"This is a powerful system for investigating plant enzymes," Nelson said. "It enables us to characterize genes that have never been studied before and manipulate them to see how they affect the type of strigolactones being made."
Beyond agriculture, strigolactones hold promise for medical and environmental applications. Some studies suggest they could be used as anti-cancer or anti-viral agents, and there is interest in their potential role in combating citrus greening disease, which is doing large-scale damage to citrus crops in Florida.
Scientists still have questions about whether the weed suicide strategy will work in real-world fields. "We're testing whether we can fine-tune the chemical signal to be even more effective," Nelson said. "If we can, this could be a game-changer for farmers battling these weeds."
This research was supported by the NSF-funded Plants3D traineeship program, led by distinguished UCR professor and geneticist Julia Bailey-Serres. The program trains students to design original biology and engineering solutions to the projected problem of massive-scale global food insecurity.
"The program is so exciting because it helps students learn to use the most cutting-edge technologies to increase crop yields and nutritional value, while also helping themselves professionally," Bailey-Serres said.
