Imagine being rooted in place.
Everything you need must be within your reach, including food. Rooted close to a buffet might be the perfect location.
Plants need to “eat,” just like us. Ever wonder how plants know they are hungry? How do they know what nutrients they need? What actually happens inside plants when they are starving?
These are questions that have intrigued Wolf Scheible, Ph.D., professor and plant biologist at Noble Research Institute, for most of his career.
In order for plants to overcome challenges associated with being rooted in place, scientists know there must be a lot of sophisticated coordination and communication within the plant as well as between plants and their environment. This communication enables the plants to defend themselves against threats, to survive extreme weather and to sense the availability of nutrients. Scheible and colleagues at Noble, including Michael Udvardi, Sonali Roy, Quina Nogales, Silvas Prince Kirubakaran, Clarissa Boschiero and Patrick Zhao, are working to understand these signaling pathways in plants and the corresponding genes involved in these complex communications.
If researchers can learn more about how plants speak, both to themselves and with their surroundings, they could find ways to strengthen the plant’s natural ability to thrive in challenging situations — including environments with limited nutrients.
Medicago truncatula grows in hydroponic, or water-based, tanks before peptides are introduced. This allows researchers to understand the influence of solely peptides on the plant roots’ ability to take up nutrients.
Searching for the Right Genes
Figuring out how to encourage plants to “eat” like us at a buffet, consuming more than they need while nutrients are available, is around the corner.
When a plant knows it is in a nutrient-limited environment, it sends a message to itself saying it needs to invest more resources into acquiring the nutrients.
But how does the plant “know” this? The answer is hidden in its genes, which code for specific actions that the plant then carries out. Each gene gives a unique set of instructions, and Scheible’s current research focuses on identifying the genes that enable a plant to recognize and communicate nutrient deficiencies. He is also investigating how the plants respond in those scenarios.
The quest to identify specific genes led researchers to look at peptide-encoding genes.
“Previously overlooked because of their small size, peptide-
encoding genes represent approximately 5% of the gene content in a typical plant genome,” Scheible says. “Their abundance indicates their importance. It follows that peptides, compounds consisting of 5-60 amino acids, made by these genes must also be significant.”
It turns out that peptides are as crucial to plant communication as cellphones are to us.
Peptides work like a lock and key, turning on or off plants’ responses to different stimuli and stressors. Internal long-distance communication, which allows all the parts of the plant to coordinate actions, is at least in part accomplished by peptides.
For example, when a plant’s environment is dry, a peptide signal, called CLE25, is sent from the roots to the leaves. The peptide ultimately causes stomata, pores in the leaves that enable the plant to release water vapor into the air, to close. This, in turn, preserves moisture in the plant.
Hee-Kyung Lee, Ph.D., research associate, takes a sample to help determine how a peptide affects nutrient uptake in alfalfa plants. Peptides help plants communicate within themselves, coordinating actions related to growth and protection against stressors, like drought and nutrient limitations. The research, which uses both alfalfa and the model legume Medicago truncatula, aims to find out which peptides are associated with increased root growth, changes in root architecture, nodule formation, nutrient uptake and other functions.
Peptides are now known to be involved in many steps of a plant’s growth, development and environmental interactions. Peptides influence shoot, root, flower and seed development. They also regulate the plant’s immune system, defenses against pathogens, associations with microorganisms, and other responses to environmental changes.
Scheible and colleagues are currently tasked with discovering which peptide families and individual peptides are associated with increased root growth, changes in root architecture, nodule formation, the uptake of nutrients and other functions.
“Identification is often based on guilt by association,” Scheible explains. “If the activity of a certain peptide-encoding gene increases with nitrogen limitation, for example, it may be related to the acquisition of that nutrient. The same can be said with other processes. We look for peptide-encoding genes that are induced or repressed by a specific stressor and then determine the roles of the encoded peptides in the plant, for example by asking what parts of the stress response can be reproduced by externally added synthetic peptides.”
“The goal of our research is to utilize the knowledge we learn in the lab, translate that information for continued testing in a field research situation, then apply what we learn to agriculture.” Wolf Scheible, Ph.D., professor and plant biologist
The National Science Foundation is supporting Scheible’s work to identify those peptide-encoding genes that influence nutrient uptake and to study the effect of similar synthetic peptides.
“The goal of our research is to utilize the knowledge we learn in the lab, translate that information for continued testing in a field research situation, then apply what we learn to agriculture,” Scheible says. “The hope is that we can develop synthetic peptides that will be used like a health supplement for plants. The applied peptide will trigger the plant to activate a signaling pathway that leads to the desired response.”
Quina Nogales Diaz, Ph.D., postdoctoral fellow, scans roots of plant samples as part of Wolf Scheible’s peptide research.
Tapping Into Peptide Potential
Manmade peptides are being made to mimic natural peptides. Synthetic peptides are easy to formulate, work at very low concentrations, and could be applied to roots together with liquid fertilizers or as foliar sprays.
Applying peptides associated with nutrient uptake, in conjunction with precision agriculture (using only the right amount at the right time in the right places), could increase yields and significantly decrease fertilizer use. Synthetic peptides may present a significant ecological and economic advantage.
Legumes have the ability to make their own meal of nitrogen from the atmosphere thanks to their symbiotic relationship with nitrogen-fixing rhizobia bacteria.
“In one of the legumes we study, we found peptides that control nodule and root development,” Scheible says. “Increasing nodule development may further lessen the need for nitrogen fertilizers. One of the next steps is to apply the synthetic peptides to study their effects on nodule development in a greenhouse and eventually field setting.”
We eat more at a buffet simply because there is an abundance of food. If we can apply peptides to tell plants that they should take up more than they currently need when nutrients are readily available, not only could the amount of fertilizer that is applied be reduced but the amount lost to the environment may be decreased as well, Scheible states.
Plants typically use less than half of the nitrogen fertilizer and only 25-35% of the phosphate fertilizer applied. A fraction of the excess phosphorus is used by soil organisms or competing weeds, but the remaining phosphorus eventually becomes an environmental problem. Immobilized and bound to the soil particles, phosphorus ends up in rivers, lakes and seas as soils erode. Toxic algae blooms and subsequent depletion of oxygen in water is due in part to phosphorus contamination.
Applying a synthetic peptide that would encourage plants to “eat” more of the available phosphate would limit the needed field applications while also preserving the world’s limited phosphorus reserves.
Wolf Scheible, Ph.D., shares the potential of peptides to improve plant performance and decrease fertilizer use when applied in conjunction with precision agriculture (using only the right amount at the right time in the right places). This could present farmers and ranchers with an ecological and economic advantage.
“The use of synthetic peptides will likely provide an alternative to genetic modification of plants,” Scheible says. “We will be able to achieve the desired results with bioactive peptides without lengthy plant breeding programs and concerns associated with genetic modifications.”
Scheible and his colleagues hope to expand their research to identifying peptide-encoding genes in fungi, bacteria and soil microbes. This will shed light on the complicated good or bad interactions between plants and other organisms.
“We already know nematodes produce peptides that influence plant development, and they are nearly identical in structure to plant peptides,” Scheible says. “However, the majority of soil biology remains a mystery. Discovering the interactions and communication pathways between soil organisms and plants will lead to continued advances in agriculture.”
With the use of peptides, it is theoretically possible to stimulate crop or forage growth without stimulating competing species of plants. Scheible is excited about the future of peptide research and the real-world applications. The possibilities are virtually endless.
Synthetic peptides hold promise as potential agrochemicals to improve plant performance and provide economically and environmentally sound options while enabling plants to belly up to the nutrient buffet we provide.