Plants have an immune system, like people, and when it is triggered by threats like disease or pests, a plant's defenses are activated. But there's a downside to this protective mechanism: The plant's growth is suppressed when its immune system is turned on.
Colorado State University researchers have found a way to boost a plant's growth while maintaining its immunity through a hormone treatment that shows promise for food production.
A plant threatened by disease will defend itself by producing hormones that can keep the plant alive but also stunt its growth – which is a problem if the plant is needed for food. By genetically manipulating the hormonal response of a commonly studied plant, scientists have harnessed the best of both worlds – immunity and productivity – and they believe this can be reproduced in crops. Their findings were published Feb. 23 in Current Biology.
"Only time will tell once it's integrated into crops what effect this will have, but it does have the potential to be as big of a breakthrough as the Green Revolution 60 years ago in terms of food security," said Cris Argueso, an associate professor in CSU's Department of Agricultural Biology and senior author of the study.
During the Green Revolution, geneticist and plant pathologist Norman Borlaug identified a wheat mutation that dramatically increased yield. He developed cultivars that were grown around the world, preventing famine. Borlaug is credited with saving a billion people from starvation and received a Nobel Peace Prize for his discovery. Downsides of the Green Revolution included widespread use of chemical fertilizers and pesticides and environmental degradation.
If the CSU researchers are successful in genetically altering crops to be more productive and disease resistant, the crops will need less fertilizer to grow and fewer chemicals to prevent disease, making this revolution "greener." Of course, adding fertilizer will always enhance growth, even in plants that are naturally productive; but for now, the researchers are focused on integrating these beneficial traits into important food crops – wheat, corn and soybeans.
"We want to create crop plants that can defend really well against pathogens but don't have a yield penalty, which is the dream for farmers," Argueso said. "We joke that this is the 'green' Green Revolution."
The plant's 'chemical brain'
One similarity between Borlaug's work and Argueso's is that her lab is also working with a hormone mutant. The researchers studied a model plant species called Arabidopsis thaliana, also known as thale cress, a well-known plant in the mustard family. They selected plants of this species that had an autoimmune mutation that prevents them from thriving – like having an autoimmune disorder.
Plants react to the constantly changing conditions surrounding them through plant-specific hormones called phytohormones. Argueso calls this the plant's "chemical brain." When plants are stressed by pests or disease, cytokinin hormones, which are responsible for cell division, are suppressed in a growth-defense tradeoff. By understanding phytohormone interactions and restoring cytokinin levels in the plants with overactive immune systems, the scientists were able to restart growth without negatively impacting the plant's defenses. In fact, the plants they designed were even more resistant to disease.
While the researchers' approach relies on genetic manipulation to change a plant's chemical signals, it is much faster and easier than identifying and altering the specific gene responsible by mapping the plant's entire genome, as is standard practice for modifying crop traits. Argueso likens their simpler solution to how a doctor might prescribe a pill to correct a chemical imbalance. She expects the mutations they've developed to be useful for agriculture for decades.
"We are exploring collaborations with breeding programs across the world, so this can be tested in different regions with all sorts of crops," Argueso said. "If these mutations have the potential that we think they do, we would like them to be used everywhere."
Student research
The study was funded by the National Science Foundation and led by Grace Johnston, who conducted the research as a student. Johnston was recruited into Argueso's lab as an undergraduate biology student and wrote the paper as her master's thesis. She is now a research associate in the lab.
"I did not know I wanted to do plant science," said Johnston, who credits Argueso's mentoring for her achievement and love of plant biology. "By the time I was done with my undergrad degree, we still didn't know enough about these plants, and I just couldn't let it go."
Johnston received prestigious fellowships from the National Science Foundation and the American Society of Plant Biologists to support her work while earning her undergraduate and graduate degrees.
"This is a CSU research success story," Johnston said. "Cris took me on when I didn't know anything about science, and here we are eight years later, and we have the opportunity to actually impact food security."
Argueso is passionate about inspiring young researchers like Johnston. Students from her lab have gone on to receive important national and international awards, and currently three undergraduate researchers are part of her team.
Second author Hannah Berry was a CSU Cell and Molecular Biology graduate student in Argueso's lab; she is now a scientist at Pairwise, a plant biotechnology and gene-editing company. Co-author Hitoshi Sakakibara, a plant science professor at Nagoya University and the RIKEN Center for Sustainable Resource Science in Japan, is one of the top plant hormone quantification experts in the world. Mikiko Kojima, a scientist at the RIKEN Center for Sustainable Resource Science, also contributed to the study.
