Out of sight, out of mind. Roots perform a lot of heavy lifting for crop development, but do they get the attention they deserve? Researchers say no and are taking a fresh look at the mechanisms that influence root development and, in turn, yield.
"Roots are important but often ignored," said Philip Benfey, Duke University biology professor and Howard Hughes Medical Institute (HHMI) investigator. "Roots obviously anchor the plant and are the primary source of water and nutrient absorption. But, the root system is complex, and we traditionally have not bred plants for better roots."
Guru Rao, Iowa State University professor of biochemistry, biophysics and molecular biology, believes root research is critical for future growth of crop yields, especially as farming becomes more precise and predictive.
"When a root system is extensive, there is a better ability to perform," he said. "Identifying genes and establishing a fundamental understanding of how root cells specialize affords opportunities to increase agricultural yields by breeding crop plants adaptable to growth in a variety of climatic conditions, especially a water-deficit environment."
THE ROOT OF PRODUCTIVITY
Rao and his research team have collaborated with scientists worldwide on the discovery of a protein that regulates formative cell division in the Arabidopsis root, a plant frequently used for research. He said previous studies found the protein ACR4 is the central player in the processes of both maintaining stem cell identity and lateral root initiation during development. The protein phosphatase, or PP2A-3, is a major player and regulator of that ACR4-mediated stem cell differentiation and primary root development.
"Most crops—including corn and soybeans—have similar genes for ACR4 and PP2A-3," he said. "We want to understand the role of these proteins or genes in root formation. Several groups of proteins exist. We are working with just one of them to manipulate the system."
Rao said root formation is affected by environmental signals. "When someone pinches you, you scream. That's a signaled response," he explained. "Plants have the same mechanism, although it is more complex. Plants can't move to avoid stress like we can. They have to adapt."
As such, Rao is evaluating when the signaling mechanism in roots is disturbed, whether researchers can influence the response in a more productive way.
"At some point, perhaps we can take three or four protein genes and affect root development so plants can grow in traditional drought areas because we create a massive root system," he said.
Benfey is working with rice and corn to analyze root development. His goal is to discover information that leads to breeding opportunities for better roots. The challenge, he said, has been the technology available to analyze real-time root development.
His research involves growing plants in a transparent gel in containers situated on a turntable, so he can take 3-D images of root development. In addition, he has tested improved X-ray technology from the medical field to try to capture root images in the soil.
"Soil is a tough environment to assess roots, but we need to be able to do it in the field under real conditions. Options have been limited because the resolution is not perfect," he said.
Benfey cofounded Hi Fidelity Genetics, which created a prototype root tracker system to sense real-time, noninvasive root development through the growing season. It's currently being tested.
"The next step will be to take data and use it to enhance breeding for specific root development," he said. "While initial research may focus on developing crops with root systems that tolerate drought, other characteristics that might contribute to greater yield potential are possible."
For example, breeders might select corn inbreds capable of generating the deepest roots and develop hybrids that respond effectively in drought situations. Another opportunity might be to choose inbreds with shallow roots that can be used in environments where phosphorus is limiting.
"More roots is not always the answer," Benfey pointed out. "We need to optimize roots for specific situations, just as we do with other plant parts, to improve yield by limiting loss to stresses."
Benfey predicts disease management and better nitrogen use efficiency also are possible. Neither he or Rao have a timetable for when such crops might be commercially available.
"As we gain more knowledge, we can make designer crops. Roots are so essential to plant development that the ramifications of healthy roots on yield are many," Rao said. "If we take what we know now with what we are learning and put it in a database, we can combine the tools together to come up with better plants. Root development is just one piece of the puzzle."
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