A team of plant scientists in Penn State's College of Agricultural Sciences has received a $1.96 million, five-year grant from the National Institutes of Health (NIH) to fund a study of how beneficial plant-bacteria partnerships evolve, persist, and can be harnessed to improve health and agriculture.
This grant, called a Maximizing Investigator's Research Award, supports a lab's long-term research vision rather than an individual project.
"Most research focuses on harmful microbes known as pathogens, but this team studies mutualisms - relationships in which both partners benefit," said team leader Liana Burghardt, an assistant professor in the Department of Plant Science and the director of the Huck Center for Root and Rhizosphere Biology.
Her laboratory group studies a well-known plant-bacteria partnership involving a plant called Medicago truncatula with the bacteria Sinorhizobium meliloti. The plant, commonly called barrel medic, is a small, annual, clover-like legume native to the Mediterranean region. It is widely used as a model organism for legume biology, a nutrient conversion process called nitrogen fixation and the study of symbiotic partnerships. It is also closely related to the forage crop alfalfa.
According to Burghardt, the mutually beneficial relationship works like this: Bacteria in the soil infect plant roots. The plant forms nodules - tiny structures - on the roots. Inside those nodules, bacteria convert the atmospheric nitrogen into usable nutrients for the plant, and the plant provides the bacteria with sugars for food. In other words, she noted, the plant gets nutrients and the bacteria get energy and a place to live.
"Similar to many environmental pathogens, these beneficial partners can live independently, and they re-form their relationship every generation," Burghardt said. "Bacteria spend much of their time in soil, not inside plants. This creates a complex situation where bacteria must survive in soil, compete to infect plants and adapt to different plant hosts."
This NIH-funded research project focuses on three big unknowns, Burghardt explained: What genes make bacteria successful inside plants, what happens outside the host and how these partnerships stay stable over time.
To study these questions, the lab combines whole-genome sequencing - decoding all DNA in the bacteria - and bioinformatics - analyzing genetic data - with lab and field experiments. The researchers track which bacterial strains succeed, how gene strain frequencies change over time, and how plant and bacterial genes interact.
If the team can figure out which genes and processes are important when microbes live outside the host in soil in this beneficial model system, Burghardt said, the researchers can infer what might happen when more nefarious bacteria - which are harder and riskier to study - grow and evolve, separated from their hosts.
"A win-win from the lab's perspective is that this knowledge also could improve agriculture by advancing the engineering of nitrogen-fixing bacteria that thrive in soil and benefit plants," she said. "It could improve agriculture by enhancing the use of natural fertilizers via nitrogen-fixing bacteria."
More broadly, this work could result in the design of better probiotics for plants or other systems, Burghardt added.
"We need to understand how and why beneficial microbes support health in general ecosystems," she said. "Our long-term goal is to use helpful microbes to improve the health of plants, animals and environments."
Other members of the research team include postdoctoral researchers Sohini Guha and Kayla Clouse; lab manager Cody DePew; and graduate students Jennifer Harris, Maria Alejandra Gil-Polo, Patrick Sydow, Kelsey Mercurio and Amanda Jason.
